["30 SEC TION II High-Yield General Principles ` \u2009N O T E S","HIGH-YIELD PRINCIPLES IN Biochemistry \u201cThe nitrogen in our DNA, the calcium in our teeth, the iron in our blood, `\tMolecular\t 32 the carbon in our apple pies were made in the interiors of collapsing stars. We are made of starstuff.\u201d `\tCellular\t 44 \u2014Carl Sagan `\tLaboratoryTechniques\t 50 \u201cBiochemistry is the study of carbon compounds that crawl.\u201d `\tGenetics\t 54 \u2014Mike Adams `\tNutrition\t 63 \u201cThe power to control our species\u2019 genetic future is awesome and terrifying.\u201d `\tMetabolism\t 71 \u2014A Crack in Creation \u201cNothing in this world is to be feared, it is only to be understood.\u201d \u2014Marie Curie This high-yield material includes molecular biology, genetics, cell biology, and principles of metabolism (especially vitamins, cofactors, minerals, and single-enzyme-deficiency diseases). When studying metabolic pathways, emphasize important regulatory steps and enzyme deficiencies that result in disease, as well as reactions targeted by pharmacologic interventions. For example, understanding the defect in Lesch-Nyhan syndrome and its clinical consequences is higher yield than memorizing every intermediate in the purine salvage pathway. Do not spend time learning details of organic chemistry, mechanisms, or physical chemistry. Detailed chemical structures are infrequently tested; however, many structures have been included here to help students learn reactions and the important enzymes involved. Familiarity with the biochemical techniques that have medical relevance\u2014such as ELISA, immunoelectrophoresis, Southern blotting, and PCR\u2014is useful. Review the related biochemistry when studying pharmacology or genetic diseases as a way to reinforce and integrate the material. 31 uploaded by medbooksvn","32 SEC TION II Biochemistry\u2003 \uf07d\u2009BIOCHEMISTRY\u2014Molecular ` \u2009B I O C H E M I S T R Y \u2014 M O L E C U L A R Chromatin structure DNA exists in the condensed, chromatin form to DNA has \u229d charge from phosphate groups. fit into the nucleus. DNA loops twice around a Histones are large and have \u2295 charge from histone octamer to form a nucleosome (\u201cbeads lysine and arginine. on a string\u201d). H1 binds to the nucleosome and to \u201clinker DNA,\u201d thereby stabilizing the In mitosis, DNA condenses to form chromatin fiber. chromosomes. DNA and histone synthesis occurs during S phase. Mitochondria have their own DNA, which is circular and does not utilize histones. DNA double-helix H1 histone DNA (linker) Nucleosome Euchromatin (H2A, H2B, H3, H4) 2 Supercoiled structure Heterochromatin Heterochromatin Condensed, appears darker on EM (labeled H Metaphase AE in A ; Nu, nucleolus). Sterically inaccessible, chromosome thus transcriptionally inactive. \u008f\u00a0methylation, H \u0090\u00a0acetylation. Heterochromatin = highly condensed. Nu Barr bodies (inactive X chromosomes) may be visible on the periphery of nucleus. Euchromatin Less condensed, appears lighter on EM (labeled Eu = true, \u201ctruly transcribed.\u201d DNA methylation E in A ). Transcriptionally active, sterically Euchromatin is expressed. accessible. Histone methylation DNA is methylated in imprinting. Histone acetylation Changes the expression of a DNA segment Methylation within gene promoter (CpG islands) Histone deacetylation without changing the sequence. Involved with aging, carcinogenesis, genomic imprinting, typically represses (silences) gene transcription. transposable element repression, and X CpG methylation makes DNA mute. chromosome inactivation (lyonization). Dysregulated DNA methylation is implicated in Usually causes reversible transcriptional Fragile X syndrome. suppression, but can also cause activation depending on location of methyl groups. Histone methylation mostly makes DNA mute. Lysine and arginine residues of histones can be Removal of histone\u2019s \u2295 charge \u008e relaxed DNA coiling \u008e\u00a0\u008f transcription. methylated. Removal of acetyl groups \u008e tightened DNA Thyroid hormone synthesis is altered by coiling \u008e\u00a0\u0090\u00a0transcription. acetylation of thyroid hormone receptor. Histone acetylation makes DNA active. Histone deacetylation may be responsible for altered gene expression in Huntington disease. Histone deacetylation deactivates DNA.","Biochemistry\u2003 \uf07d\u2009BIOCHEMISTRY\u2014Molecular SEC TION II 33 Nucleotides Nucleoside = base + (deoxy)ribose (sugar). Nucleotide = base + (deoxy)ribose + phosphate; 5\u2032 end of incoming nucleotide bears the linked by 3\u2032-5\u2032 phosphodiester bond. triphosphate (energy source for the bond). \u03b1-Phosphate is target of 3\u2032 hydroxyl attack. Purines (A,G)\u20142 rings. Pure As Gold. Pyrimidines (C,U,T)\u20141 ring. CUT the pyramid. Thymine has a methyl. Deamination reactions: C-G bond (3 H bonds) stronger than A-T bond Cytosine \u008e uracil Adenine \u008e hypoxanthine (2 H bonds). \u008f\u00a0C-G content \u008e\u00a0\u008f\u00a0melting Guanine \u008e xanthine temperature of DNA. \u201cC-G bonds are like 5-methylcytosine \u008e thymine Crazy Glue.\u201d Uracil found in RNA; thymine in DNA. Amino acids necessary for purine synthesis (cats Methylation of uracil makes thymine. purr until they GAG): Glycine Aspartate Glutamine Purine (A, G) Pyrimidine (C, U, T) CO2 Carbamoyl Aspartate Glycine phosphate C Aspartate CN NC THF NC CC C THF N CC NN Glutamine uploaded by medbooksvn","34 SEC TION II Biochemistry\u2003 \uf07d\u2009BIOCHEMISTRY\u2014Molecular De novo pyrimidine Various immunosuppressive, antineoplastic, and antibiotic drugs function by interfering with and purine synthesis nucleotide synthesis: Pyrimidine base production Ribose 5-P Purine base production or Pyrimidine synthesis: (requires aspartate) reuse from salvage pathway \u0083\t Leflunomide: inhibits dihydroorotate Glutamine + CO\u2082 (de novo requires aspartate, dehydrogenase glycine, glutamine, and THF) \u0083\t 5-fl orouracil (5-FU) and its prodrug 2 ATP CPS2 (carbamoyl PRPP (phosphoribosyl capecitabine: form 5-F-dUMP, which inhibits 2GlAuDtaPm+aPtei + phosphate pyrophosphate) synthetase thymidylate synthase (\u0090\u00a0dTMP) synthetase II) Purine synthesis: Carbamoyl phosphate \u0083\t 6-mercaptopurine (6-MP) and its prodrug azathioprine: inhibit de novo purine synthesis Aspartate (guanine phosphoribosyltransferase); azathioprine is metabolized via purine Le\ufb02unomide 6-MP, MTX, azathioprine degradation pathway and can lead to immunosuppression when administered with Orotic PRPP xanthine oxidase inhibitor acid \u0083\t Mycophenolate and ribavirin: inhibit inosine Impaired in UMP IMP Mycophenolate, monophosphate dehydrogenase orotic aciduria UDP ribavirin Hydroxyurea Purine and pyrimidine synthesis: Rirbedouncutcalseeotide AMP GMP \u0083\t Hydroxyurea: inhibits ribonucleotide dUDP CTP reductase N5N10- dUMP \u0083\t Methotrexate (MTX), trimethoprim (TMP), Thymidylate and pyrimethamine: inhibit dihydrofolate methylene THF synthase reductase (\u0090\u00a0deoxythymidine monophosphate [dTMP]) in humans (methotrexate), THF 5-FU bacteria (trimethoprim), and protozoa (pyrimethamine) Driehdydurcotafoselate DHF dTMP MTX, TMP, pyrimethamine CPS1 = m1tochondria, urea cycle, found in liver CPS2 = cytwosol, pyrimidine synthesis, found in most cells","Biochemistry\u2003 \uf07d\u2009BIOCHEMISTRY\u2014Molecular SEC TION II 35 Purine salvage deficiencie Nucleic acids Ribose 5-phosphate Nucleic acids Catabolism (DNA and RNA) Nucleic acids AMP PRPP synthetase De novo synthesis Salvage Nucleotides GMP IMP Cladribine, pentostatin Nucleosides Guanosine Lesch-Nyhan Inosine ADA Adenosine APRT syndrome SCID PRPP HGPRT Free bases Guanine Hypoxanthine Adenine PRPP XO Degradation and salvage Xanthine Allopurinol XO Febuxostat Uric acid Urate oxidase (rasburicase)a Allantoin Excretion aAbsent in humans. ADA, adenosine deaminase; APRT, adenine phosphoribosyltransferase; HGPRT, hypoxanthine guanine phosphoribosyltransferase, XO, xanthine oxidase; SCID, severe combined immune de\ufb01ciency (autosomal recessive inheritance) Adenosine deaminase ADA is required for degradation of adenosine One of the major causes of autosomal recessive deficiency and deoxyadenosine. \u0090\u00a0ADA \u008e\u00a0\u008f\u00a0dATP SCID. \u008e\u00a0\u0090\u00a0ribonucleotide reductase activity \u008e\u00a0\u0090\u00a0DNA precursors in cells \u008e\u00a0\u0090\u00a0lymphocytes. Lesch-Nyhan Defective purine salvage. Absent HGPRT HGPRT: syndrome \u008e\u00a0\u0090\u00a0GMP (from guanine) and\u00a0\u0090\u00a0IMP (from Hyperuricemia hypoxanthine) formation. Compensatory \u008f\u00a0in Gout purine synthesis (\u008f\u00a0PRPP amidotransferase Pissed off (aggression, self-mutilation) activity) \u008e\u00a0excess uric acid production. Red\/orange crystals in urine X-linked recessive. Tense muscles (dystonia) Findings: intellectual disability, self-mutilation, Treatment: allopurinol, febuxostat. aggression, hyperuricemia (red\/orange \u201csand\u201d [sodium urate crystals] in diaper), gout, dystonia, macrocytosis. Genetic code features Each codon specifies only 1 amino acid. Unambiguous Degenerate\/ Most amino acids are coded by multiple codons. Exceptions: methionine (AUG) and tryptophan redundant (UGG) encoded by only 1 codon. Wobble hypothesis\u2014first 2 nucleotides of Commaless, codon are essential for anticodon recognition Exceptions: some viruses. nonoverlapping while the 3rd nucleotide can differ (\u201cwobble\u201d). Exception in humans: mitochondria. Universal Read from a fixed starting point as a continuous sequence of bases. Genetic code is conserved throughout evolution. uploaded by medbooksvn","36 SEC TION II Biochemistry\u2003 \uf07d\u2009BIOCHEMISTRY\u2014Molecular DNA replication Occurs in 5\u2032\u00a0\u008e\u00a03\u2032 direction (\u201c5ynth3sis\u201d) in continuous and discontinuous (Okazaki fragment) fashion. Origin of Semiconservative. More complex in eukaryotes than in prokaryotes, but shares analogous enzymes. replication\u00a0 A Replication fork\u00a0 B Particular consensus sequence in genome AT-rich sequences (eg, TATA box regions) are Helicase\u00a0 C where DNA replication begins. May be single found in promoters (often upstream) and (prokaryotes) or multiple (eukaryotes). origins of replication (ori). Single-stranded binding proteins\u00a0 D Y-shaped region along DNA template where DNA leading and lagging strands are synthesized. topoisomerases\u00a0 E Unwinds DNA template at replication fork. Helicase halves DNA. Primase\u00a0 F Deficient in Bloom syndrome (BLM gene DNA polymerase III\u00a0 G mutation). DNA polymerase I\u00a0 H DNA ligase\u00a0 I Prevent strands from reannealing or degradation Telomerase by nucleases. Creates a single- (topoisomerase I) or double- In eukaryotes: irinotecan\/topotecan inhibit (topoisomerase II) stranded break in the helix topoisomerase (TOP) I, etoposide\/teniposide to add or remove supercoils (as needed due to inhibit TOP II. underwinding or overwinding of DNA). In prokaryotes: fluoroquinolones inhibit TOP II (DNA gyrase) and TOP IV. Makes RNA primer for DNA polymerase III to initiate replication. Prokaryotes only. Elongates leading strand DNA polymerase III has 5\u2032 \u008e 3\u2032 synthesis and by adding deoxynucleotides to the 3\u2032 end. proofreads with 3\u2032 \u008e 5\u2032 exonuclease. Elongates lagging strand until it reaches primer of preceding fragment. Drugs blocking DNA replication often have a modified 3\u2032 OH, thereby preventing addition of the next nucleotide (\u201cchain termination\u201d). Prokaryotes only. Degrades RNA primer; Same functions as DNA polymerase III, also replaces it with DNA. excises RNA primer with 5\u2032 \u008e 3\u2032 exonuclease. Catalyzes the formation of a phosphodiester Joins Okazaki fragments. bond within a strand of double-stranded DNA. Ligase links DNA. Eukaryotes only. A reverse transcriptase (RNA- Upregulated in progenitor cells and also often in dependent DNA polymerase) that adds DNA cancer; downregulated in aging and progeria. (TTAGGG) to 3\u2032 ends of chromosomes to avoid loss of genetic material with every duplication. Telomerase TAGs for Greatness and Glory. E 3' Topoisomerase 5' C A Helicase Origin of replication Leading strand B G Replication fork DNA polymerase Lagging strand 3' 5' D Okazaki fragment Single-stranded Area of interest A binding protein RNA primer Leading strand Origin of replication F I Fork Lagging strand Primase DNA ligase movement Fork movement Lagging strand Leading strand H DNA polymerase I","Biochemistry\u2003 \uf07d\u2009BIOCHEMISTRY\u2014Molecular SEC TION II 37 DNA repair Brings together 2 ends of DNA fragments to Double strand break 53\u00b4\u00b4 Double strand bre Double strand repair double-stranded breaks. 53\u00b4\u00b4 35\u00b4\u00b4 5\u00b4 Nonhomologous end 3\u00b4 joining Homology not required. Part of the DNA may be Nonhomologous end joining lost or translocated. Homologous recombination May be dysfunctional in ataxia telangiectasia. Single strand Requires 2 homologous DNA duplexDeousb.leAstrand break 3\u00b4 5\u00b4 Double strand break 3\u00b4 Nucleotide excision strand from damaged dsD53N\u00b4\u00b4 A is repaired 5\u00b4 3\u00b4 5\u00b4 repair using a complementary strand from intact 53\u00b4\u00b4 35\u00b4\u00b4 Homologous recombin Base excision repair homologous dsDNA as a temNopnlhaotem.ologous end joining Mismatch repair Defective in breast\/ovarian cancers with BRCA1 or BRCA2 mutations and in Fanconi anemia. Restores duplexes accurately without loss of nucleotides. Homologous recombination Specific endonucleases remove the Occurs in G1 phase of cell cycle. oligonucleotides containing damaged bases; Defective in xeroderma pigmentosum DNA polymerase and ligase fill and reseal the gap, respectively. Repairs bulky helix-distorting (inability to repair DNA pyrimidine dimers lesions (eg, pyrimidine dimers). caused by UV exposure). Presents with dry skin, photosensitivity, skin cancer. Base-specific Glycosylase removes altered base Occurs throughout cell cycle. and creates AP site (apurinic\/apyrimidinic). Important in repair of spontaneous\/toxic One or more nucleotides are removed by deamination. AP-Endonuclease, which cleaves 5\u2032 end. AP- \u201cGEL Please.\u201d Lyase cleaves 3\u2032 end. DNA Polymerase-\u03b2 fills the gap and DNA ligase seals it. Occurs predominantly in S phase of cell cycle. Defective in Lynch syndrome (hereditary Mismatched nucleotides in newly synthesized strand are removed and gap is filled and nonpolyposis colorectal cancer [HNPCC]). resealed. UV exposure Pyrimidine dimer Deaminated C TT U G AA G A T T Endonucleases remove AP U G Mismatched segment damaged segment site Glycosylase removes base removed G AA Endonuclease and lyase A remove backbone segment Newly replaced segment G T TT A AA U G Mismatch repair Nucelotide excision repair Base excision repair C A B uploaded by medbooksvn","38 SEC TION II Biochemistry\u2003 \uf07d\u2009BIOCHEMISTRY\u2014Molecular Mutations in DNA Degree of change: silent << missense < nonsense < frameshift. Single nucleotide substitutions are repaired by DNA polymerase and DNA ligase. Types of single nucleotide (point) mutations: \u0083\t Transition\u2014purine to purine (eg, A to G) or pyrimidine to pyrimidine (eg, C to T). \u0083\t Transversion\u2014purine to pyrimidine (eg, A to T) or pyrimidine to purine (eg, C to G). Single nucleotide substitutions Silent mutation Codes for same (synonymous) amino acid; often involves 3rd position of codon (tRNA wobble). Missense mutation Results in changed amino acid (called conservative if new amino acid has similar chemical structure). Examples: sickle cell disease (substitution of glutamic acid with valine). Nonsense mutation Results in early stop codon (UGA, UAA, UAG). Usually generates nonfunctional protein. Stop the nonsense! Other mutations Frameshift mutation Deletion or insertion of any number of nucleotides not divisible by 3 \u008e\u00a0misreading of all nucleotides downstream. Protein may be shorter or longer, and its function may be disrupted or altered. Examples: Duchenne muscular dystrophy, Tay-Sachs disease, cystic fibrosis. Splice site mutation Retained intron in mRNA \u008e\u00a0protein with impaired or altered function. Examples: rare causes of cancers, dementia, epilepsy, some types of \u03b2-thalassemia, Gaucher disease, Marfan syndrome. Original Silent Missense Nonsense Frameshift Frameshift sequence mutation mutation mutation insertion T deletion Coding DNA 5\u00b4 G A G GAA GTG T AG GA G G G A C 3\u00b4 mRNA codon 5\u00b4 G A G GAA GUG UAG GAU G A C 3\u00b4 Amino acid Glu Glu Val Stop Asp Asp Altered amino acids Lac operon Classic example of a genetic response to an environmental change. Glucose is the preferred metabolic substrate in E coli, but when glucose is absent and lactose is available, the lac operon is CAP activated to switch to lactose metabolism. Mechanism of shift: \u0083\t Low glucose \u008e\u00a0\u008f\u00a0adenylate cyclase activity \u008e\u00a0\u008f\u00a0generation of cAMP from ATP \u008e\u00a0activation of catabolite activator protein (CAP) \u008e\u00a0\u008f\u00a0transcription. \u0083\t High lactose \u008e\u00a0unbinds repressor protein from repressor\/operator site \u008e\u00a0\u008f\u00a0transcription. Adenylate Glucose cAMP cyclase Binds CAP site, ATP RNA induces transcription Lac operon CAP polymerase DNA Lacl CAP site Promoter Operator LacZ LacY LacA STATE Lac genes strongly expressed genes blBoinckdss torapnesractroiprt,ion Low glucose Repressor protein Lactose available Lac genes not expressed High glucose Repressor Lactose unavailable CAP Lac genes not expressed protein site P O Very low (basal) expression Low glucose Lactose unavailable High glucose Lactose available Allolactose Inactivated (inducer) repressor","Biochemistry\u2003 \uf07d\u2009BIOCHEMISTRY\u2014Molecular SEC TION II 39 Functional Enhancer\/ Promoter 5\u00b4 UTR Open reading frame 3\u00b4 UTR Silencer organization of a silencer Intron Exon Intron eukaryotic gene GT AG GT AG Exon Exon DNA Intron Exon Intron (coding strand) 5\u00b4 CAAT TATAAA GU AG GU AG AATAAA 3\u00b4 Transcription CAAT Box TATA Box Polyadenylation signal Transcription start Pre-mRNA Splicing Exon Exon AAUAAA Mature mRNA 5\u00b4 cap Protein coding region Translation AUG start codon Stop AAUAAA AAAAAA Poly-A tail Protein Regulation of gene expression Promoter Site where RNA polymerase II and multiple Promoter mutation commonly results in other transcription factors bind to DNA dramatic \u0090\u00a0in level of gene transcription. upstream from gene locus (AT-rich upstream sequence with TATA and CAAT boxes, which Enhancers and silencers may be located close to, differ between eukaryotes and prokaryotes). far from, or even within (in an intron) the gene Promoters increase ori activity. whose expression they regulate. Enhancer DNA locus where regulatory proteins Primary mechanisms of epigenetic change (\u201cactivators\u201d) bind,\u00a0increasing expression of a include DNA methylation, histone gene on the same chromosome. modification, and noncoding RNA. Silencer DNA locus where regulatory proteins (\u201crepressors\u201d) bind, decreasing expression of a gene on the same chromosome. Epigenetics Changes made to gene expression (heritable mitotically\/meiotically) without a change in underlying DNA sequence. uploaded by medbooksvn","40 SEC TION II Biochemistry\u2003 \uf07d\u2009BIOCHEMISTRY\u2014Molecular RNA processing Initial transcript is called heterogeneous nuclear Poly-A polymerase does not require a template. (eukaryotes) RNA (hnRNA). hnRNA is then modified and AAUAAA = polyadenylation signal. Mutation becomes mRNA. Cap Coding in polyadenylation signal \u008e early degradation 5' Gppp The following processes occur in the nucleus: prior to translation. \u0083\t Capping of 5\u2032 end (addition of Kozak sequence\u2014initiation site in most 3' 7-methylguanosine cap; cotranscriptional) eukaryotic mRNA. Facilitates binding of small HO-AAAAA \u0083\t Polyadenylation of 3\u2032 end (\u223c200 A\u2019s \u008e\u00a0poly-A subunit of ribosome to mRNA. Mutations Tail tail; posttranscriptional) in sequence\u00a0\u008e\u00a0impairment of initiation of \u0083\t Splicing out of introns (posttranscriptional) translation\u00a0\u008e\u00a0\u0090\u00a0protein synthesis. Capped, tailed, and spliced transcript is called mRNA. mRNA is transported out of nucleus to be translated in cytosol. mRNA quality control occurs at cytoplasmic processing bodies (P-bodies), which contain exonucleases, decapping enzymes, and microRNAs; mRNAs may be degraded or stored in P-bodies for future translation. RNA polymerases RNA polymerase I makes rRNA, the most I, II, and III are numbered in the same order Eukaryotes common (rampant) type; present only in that their products are used in protein nucleolus. synthesis: rRNA, mRNA, then tRNA. Prokaryotes RNA polymerase II makes mRNA (massive), \u03b1-amanitin, found in Amanita phalloides (death microRNA (miRNA), and small nuclear RNA cap mushrooms), inhibits RNA polymerase II. (snRNA). Causes dysentery and severe hepatotoxicity if ingested. RNA polymerase III makes 5S rRNA, tRNA (tiny). Dactinomycin inhibits RNA polymerase in both prokaryotes and eukaryotes. No proofreading function, but can initiate chains. RNA polymerase II opens DNA at Rifamycins (rifampin, rifabutin) inhibit DNA- promoter site. dependent RNA polymerase in prokaryotes. 1 RNA polymerase (multisubunit complex) makes all 3 kinds of RNA.","Biochemistry\u2003 \uf07d\u2009BIOCHEMISTRY\u2014Molecular SEC TION II 41 Introns vs exons Exons contain the actual genetic information Introns are intervening sequences and stay coding for protein or functional RNA. in the nucleus, whereas exons exit and are expressed. Introns do not code for protein, but are important in regulation of gene expression. Alternative splicing\u2014can produce a variety of protein products from a single hnRNA Different exons are frequently combined by (heterogenous nuclear RNA) sequence (eg, alternative splicing to produce a larger number transmembrane vs secreted Ig, tropomyosin of unique proteins. variants in muscle, dopamine receptors in the brain, host defense evasion by tumor cells). 5\u2032 Exon 1 Exon 2 Exon 3 Exon 4 Exon 5 Exon 6 3\u2032 3\u2032 2 5\u2032 DNA Transcription 5\u2032 34 5 3\u2032 1 Alternative splicing 6 hnRNA Splicing mRNA 5\u2032 3\u2032 5\u2032 3\u2032 5\u2032 3\u2032 1 24 56 1 3 56 1 345 6 Translation Proteins 15 15 15 42 6 6 43 6 3 Splicing of pre-mRNA Part of process by which precursor mRNA (pre-mRNA) is transformed into mature mRNA. Introns typically begin with GU and end with AG. Alterations in snRNP assembly can cause clinical disease; eg, in spinal muscular atrophy, snRNP assembly is affected due to \u0090\u00a0SMN protein \u008e\u00a0congenital degeneration of anterior horns of spinal cord \u008e\u00a0symmetric weakness (hypotonia, or \u201cfloppy baby syndrome\u201d). snRNPs are snRNA bound to proteins (eg, Smith [Sm]) to form a spliceosome that cleaves pre- mRNA. Anti-U1 snRNP antibodies are associated with SLE, mixed connective tissue disease, other rheumatic diseases. Primary transcript combines with 5\u2032 splice site U1 snRNP Branch point 3\u2032 splice site small nuclear ribonucleoproteins O P GU U2 snRNP (snRNPs) and other proteins to 5\u2032 3\u2032 form spliceosome. Exon 1 OH A AG P O Exon 2 Intron Spliceosome Cleavage at 5\u2032 splice site; lariat- UG P shaped (loop) intermediate is OH 3\u2032 generated. AAG P O Exon 1 Exon 2 Cleavage at 3\u2032 splice site; lariat Mature mRNA is released to precisely remove P + intron and join 2 exons. Exon 1 Exon 2 UG P A AG OH 3\u2032 uploaded by medbooksvn","42 SEC TION II Biochemistry\u2003 \uf07d\u2009BIOCHEMISTRY\u2014Molecular tRNA Structure 75\u201390 nucleotides, 2\u00ba structure, cloverleaf form, anticodon end is opposite 3\u2032 aminoacyl end. All Charging tRNAs, both eukaryotic and prokaryotic, have CCA at 3\u2032 end along with a high percentage of chemically modified bases. The amino acid is covalently bound to the 3\u2032 end of the tRNA. CCA Can Carry Amino acids. T-arm: contains the T\u03a8C (ribothymidine, pseudouridine, cytidine) sequence necessary for tRNA- ribosome binding. T-arm Tethers tRNA molecule to ribosome. D-arm: contains Dihydrouridine residues necessary for tRNA recognition by the correct aminoacyl- tRNA synthetase. D-arm allows Detection of the tRNA by aminoacyl-tRNA synthetase. Attachment site: 3\u2032-ACC-5\u2032 is the amino acid ACCeptor site. Aminoacyl-tRNA synthetase (uses ATP; 1 unique enzyme per respective amino acid) and binding of charged tRNA to the codon are responsible for the accuracy of amino acid selection. Aminoacyl-tRNA synthetase matches an amino acid to the tRNA by scrutinizing the amino acid before and after it binds to tRNA. If an incorrect amino acid is attached, the bond is hydrolyzed. A mischarged tRNA reads the usual codon but inserts the wrong amino acid. Structure Charging Pairing (aminoacylation) (codon-anticodon) Attachment site OH A 3\u00b4 Amino acid O A 3\u00b4 Amino acid O A 3\u00b4 C C C C C C 5\u00b4 5\u00b4 5\u00b4 T-arm D-arm ATP AMP + PPi C \u03a8T IF2 D (initiation factor) D C \u03a8T D Aminoacyl-tRNA synthetase D Variable arm D C \u03a8T D Anticodon Wobble UAC Anticodon (5\u00b4-CAU-3\u00b4) U A C loop U A C position mRNA C C C A U G A U A C Codon (5\u00b4-AUG-3\u00b4) Start and stop codons AUG. AUG inAUGurates protein synthesis. mRNA start codon Codes for methionine, which may be removed fMet stimulates neutrophil chemotaxis. Eukaryotes before translation is completed. UGA = U Go Away. UA A = U Are Away. Prokaryotes Codes for N-formylmethionine (fMet). UAG = U Are Gone. mRNA stop codons UGA, UAA, UAG. Recognized by release factors.","Biochemistry\u2003 \uf07d\u2009BIOCHEMISTRY\u2014Molecular SEC TION II 43 Protein synthesis 1.\u2002Eukaryotic initiation factors (eIFs) identify Eukaryotes: 40S + 60S \u008e 80S (even). Initiation the 5\u2032 cap. Prokaryotes: 30S + 50S \u008e 70S (prime). Synthesis occurs from N-terminus to Elongation 2.\u2002 eIFs help assemble the 40S ribosomal subunit with the initiator tRNA. C-terminus. Termination 3.\u2002 eIFs released when the mRNA and the ATP\u2014tRNA Activation (charging). ribosomal 60S subunit assemble with the GTP\u2014tRNA Gripping and Going places complex. Requires GTP. (translocation). \u0007Aminoacyl-tRNA binds to A site (except for initiator methionine, which binds the P site), Think of \u201cgoing APE\u201d: requires an elongation factor and GTP. A site = incoming Aminoacyl-tRNA. \u0007rRNA (\u201cribozyme\u201d) catalyzes peptide bond P site = accommodates growing Peptide. formation, transfers growing polypeptide to E site = holds Empty tRNA as it Exits. amino acid in A site. Ribosome advances 3 nucleotides toward 3\u2032 Elongation factors are targets of bacterial toxins end of mRNA, moving peptidyl tRNA to P (eg, Diphtheria, Pseudomonas). site (translocation). Shine-Dalgarno sequence\u2014ribosomal binding Eukaryotic release factors (eRFs) recognize the site in prokaryotic mRNA. Recognized by 16S stop codon and halt translation \u008e\u00a0completed RNA in ribosomal subunit. Enables protein polypeptide is released from ribosome. synthesis initiation by aligning ribosome with Requires GTP. start codon so that code is read correctly. 60\/50S 40\/30S 80\/70S M M R U AC M 5\u00b4 A U G C A U G A U MH Initiator tRNA EPA mRNA U A C 3\u00b4 U AC G UA Initiation 5\u00b4 A U G C A U G A U 3\u00b4 EPA Ribosome moves left to S right along mRNA H Elongation MH UGA M U AC Termination G UA GUA 3\u00b4 UAC Q 5\u00b4 A U G C A U G A U EPA 5\u00b4 A U G C A U G A U 3\u00b4 EPA Posttranslational modifi ations Trimming Removal of N- or C-terminal propeptides from zymogen to generate mature protein (eg, trypsinogen to trypsin). Covalent alterations Phosphorylation, glycosylation, hydroxylation, methylation, acetylation, and ubiquitination. Chaperone protein Intracellular protein involved in facilitating and maintaining protein folding. In yeast, heat shock proteins (eg, HSP60) are constitutively expressed, but expression may increase with high temperatures, acidic pH, and hypoxia to prevent protein denaturing\/misfolding. uploaded by medbooksvn","44 SEC TION II Biochemistry\u2003 \uf07d\u2009BIOCHEMISTRY\u2014Cellular ` \u2009B I O C H E M I S T R Y \u2014 C E LL U L A R Cell cycle phases Checkpoints control transitions between phases of cell cycle. This process is regulated by cyclins, cyclin-dependent kinases (CDKs), and tumor suppressors. M phase (shortest phase of cell cycle) REGULATION OF CELL CYCLE includes mitosis (prophase, prometaphase, metaphase, anaphase, telophase) and cytokinesis (cytoplasm splits in two). G1 is of variable duration. Cyclin-dependent kinases Constitutively expressed but inactive when not bound to cyclin. Cyclin-CDK complexes Cyclins are phase-specific regulatory proteins that activate CDKs when stimulated by growth Tumor suppressors factors. The cyclin-CDK complex can then phosphorylate other proteins (eg, Rb) to coordinate cell cycle progression. This complex must be activated\/inactivated at appropriate times for cell CELL TYPES cycle to progress. Permanent p53 \u008e\u00a0p21 induction \u008e\u00a0CDK inhibition \u008e\u00a0Rb hypophosphorylation (activation) \u008e\u00a0G1-S Stable (quiescent) progression inhibition. Mutations in tumor suppressor genes can result in unrestrained cell Labile division (eg, Li-Fraumeni syndrome). Growth factors (eg, insulin, PDGF, EPO, EGF) bind tyrosine kinase receptors to transition the cell from G1 to S phase. Remain in G0, regenerate from stem cells. Neurons, skeletal and cardiac muscle, RBCs. Enter G1 from G0 when stimulated. Hepatocytes, lymphocytes, PCT, periosteal cells. Never go to G0, divide rapidly with a short G1. Bone marrow, gut epithelium, skin, hair Most affected by chemotherapy. follicles, germ cells. Cell cycle arrest p21 Cyclin GO Cyclin CDK CDK DNA damage p21 Rb, p53 modulate G1 G1 restriction point Growth Li-Fraumeni syndrome Cytokinesis M (loss of function) MitosisG2 p53 I N T E RDPNHAASSynE thes HPV E6 BCL-2 BCL-XL Rb P BAX\/BAK P Caspase activation Apoptosis P (intrinsic pathway) Rb E2F S is E2F Gene transcription","Biochemistry\u2003 \uf07d\u2009BIOCHEMISTRY\u2014Cellular SEC TION II 45 Rough endoplasmic Site of synthesis of secretory (exported) proteins N-linked glycosylation occurs in the reticulum and of N-linked oligosaccharide addition to eNdoplasmic reticulum. lysosomal and other proteins. Mucus-secreting goblet cells of small intestine Nissl bodies (RER in neurons)\u2014synthesize and antibody-secreting plasma cells are rich in peptide neurotransmitters for secretion. RER. Free ribosomes\u2014unattached to any membrane; Proteins within organelles (eg, ER, Golgi bodies, site of synthesis of cytosolic, peroxisomal, and lysosomes) are formed in RER. mitochondrial proteins. Smooth endoplasmic Site of steroid synthesis and detoxification of Hepatocytes and steroid hormone\u2013producing reticulum drugs and poisons. Lacks surface ribosomes. cells of the adrenal cortex and gonads are rich Location of glucose-6-phosphatase (last step in in SER. both glycogenolysis and gluconeogenesis). Cell traffi ing Golgi is distribution center for proteins and lipids from ER to vesicles and plasma membrane. Posttranslational events in GOlgi include modifying N-oligosaccharides on asparagine, adding O-oligosaccharides on serine and threonine, and adding mannose-6-phosphate to proteins for lysosomal and other proteins. Endosomes are sorting centers for material from outside the cell or from the Golgi, sending it to lysosomes for destruction or back to the membrane\/Golgi for further use. I-cell disease (inclusion cell disease\/mucolipidosis type II)\u2014inherited lysosomal storage disorder (autosomal recessive); defect in N-acetylglucosaminyl-1-phosphotransferase \u008e failure of the Golgi to phosphorylate mannose residues (\u0090 mannose-6-phosphate) on glycoproteins \u008e\u00a0enzymes secreted extracellularly rather than delivered to lysosomes \u008e\u00a0lysosomes deficient in digestive enzymes \u008e\u00a0buildup of cellular debris in lysosomes (inclusion bodies). Results in coarse facial features, gingival hyperplasia, corneal clouding, restricted joint movements, claw hand deformities, kyphoscoliosis, and \u008f\u00a0plasma levels of lysosomal enzymes. Symptoms similar to but more severe than Hurler syndrome. Often fatal in childhood. Key: Plasma membrane Secretory Signal recognition particle (SRP)\u2014abundant, Clathrin vesicle cytosolic ribonucleoprotein that traffics Late polypeptide-ribosome complex from the COPI endosome Early cytosol to the RER. Absent or dysfunctional endosome SRP \u008e\u00a0accumulation of protein in cytosol. COPII Lysosome Vesicular trafficking proteins Retrograde trans \u0083\t COPI: Golgi \u008e Golgi (retrograde); cis-Golgi Anterograde \u008e\u00a0ER. Golgi \u0083\t COPII: ER \u008e\u00a0cis-Golgi (anterograde). \u201cTwo apparatus (COPII) steps forward (anterograde); one (COPI) step back (retrograde).\u201d cis \u0083\t Clathrin: trans-Golgi \u008e lysosomes; plasma membrane \u008e endosomes (receptor-mediated endocytosis [eg, LDL receptor activity]). Rough endoplasmic reticulum Nuclear envelope uploaded by medbooksvn","46 SEC TION II Biochemistry\u2003 \uf07d\u2009BIOCHEMISTRY\u2014Cellular Peroxisome Membrane-enclosed organelle involved in: \u0083\t \u03b2-oxidation of very-long-chain fatty acids (VLCFA) (strictly peroxisomal process) \u0083\t \u03b1-oxidation of branched-chain fatty acids (strictly peroxisomal process) \u0083\t Catabolism of amino acids and ethanol \u0083\t Synthesis of bile acids and plasmalogens (important membrane phospholipid, especially in white matter of brain) Zellweger syndrome\u2014autosomal recessive disorder of peroxisome biogenesis due to mutated PEX genes. Hypotonia, seizures, jaundice, craniofacial dysmorphia, hepatomegaly, early death. Refsum disease\u2014autosomal recessive disorder of \u03b1-oxidation \u008e buildup of phytanic acid due to inability to degrade it. Scaly skin, ataxia, cataracts\/night blindness, shortening of 4th toe, epiphyseal dysplasia. Treatment: diet, plasmapheresis. Adrenoleukodystrophy\u2014X-linked recessive disorder of \u03b2-oxidation due to mutation in ABCD1 gene \u008e VLCFA buildup in adrenal glands, white (leuko) matter of brain, testes. Progressive disease that can lead to adrenal gland crisis, progressive loss of neurologic function, death. Proteasome Barrel-shaped protein complex that degrades polyubiquitin-tagged proteins. Plays a role in many cellular processes, including immune response (MHC I\u2013mediated). Defects in ubiquitin-proteasome system also implicated in diverse human diseases including neurodegenerative diseases. Cytoskeletal elements A network of protein fibers within the cytoplasm that supports cell structure, cell and organelle movement, and cell division. TYPE OF FILAMENT PREDOMINANT FUNCTION EXAMPLES Microfilaments Muscle contraction, cytokinesis Actin, microvilli. Intermediate Maintain cell structure Vimentin, desmin, cytokeratin, lamins, glial filaments fibrillary acidic protein (GFAP), neurofilaments. Microtubules Movement, cell division Cilia, flagella, mitotic spindle, axonal trafficking, centrioles. Microtubule Cylindrical outer structure composed of a Drugs that act on microtubules (microtubules helical array of polymerized heterodimers get constructed very terribly): Positive of \u03b1- and \u03b2-tubulin. Each dimer has 2 GTP \u0083\t Mebendazole (antihelminthic) \u00a0\u00a0end (+) bound. Incorporated into flagella, cilia, mitotic \u0083\t Griseofulvin (antifungal) Heterodimer spindles. Also involved in slow axoplasmic \u0083\t Colchicine (antigout) transport in neurons. \u0083\t Vinca alkaloids (anticancer) Proto\ufb01lament \u0083\t Taxanes (anticancer) Molecular motor proteins\u2014transport cellular Negative cargo toward opposite ends of microtubule. Negative end near nucleus. \u00a0\u00a0end (\u2013) \u0083\t Retrograde to microtubule (+ \u008e \u2212)\u2014dynein. Positive end points to periphery. \u0083\t Anterograde to microtubule (\u2212 \u008e +)\u2014kinesin. Ready? Attack! Clostridium tetani toxin, poliovirus, rabies virus, and herpes simplex virus (HSV) use dynein for retrograde transport to the neuronal cell body. HSV reactivation occurs via anterograde transport from cell body (kinesin mediated). Slow anterograde transport rate limiting step of peripheral nerve regeneration after injury.","Biochemistry\u2003 \uf07d\u2009BIOCHEMISTRY\u2014Cellular SEC TION II 47 Cilia structure Motile cilia consist of 9 doublet + 2 singlet arrangement of microtubules (axoneme) A . Basal body (base of cilium below cell membrane) consists of 9 microtubule triplets B with no central microtubules. Nonmotile (primary) cilia work as chemical signal sensors and have a role in signal transduction and cell growth control. Dysgenesis may lead to polycystic kidney disease, mitral valve prolapse, or retinal degeneration. Axonemal dynein\u2014ATPase that links peripheral 9 doublets and causes bending of cilium by differential sliding of doublets. Gap junctions enable coordinated ciliary movement. A B Dynein arm Microtubule A Microtubule B Nexin Doublets Triplets Primary ciliary Autosomal recessive. Dynein arm defect \u008e immotile cilia \u008e dysfunctional ciliated epithelia. Most dyskinesia common type is Kartagener syndrome (PCD with situs inversus). A Developmental abnormalities due to impaired migration and orientation (eg, situs inversus A , hearing loss due to dysfunctional eustachian tube cilia); recurrent infections (eg, sinusitis, ear infections, RL bronchiectasis due to impaired ciliary clearance of debris\/pathogens); infertility (\u008f risk of ectopic pregnancy due to dysfunctional fallopian tube cilia, immotile spermatozoa). Lab findings: \u0090 nasal nitric oxide (used as screening test). Sodium-potassium Na+\/K+-ATPase is located in the plasma 2 strikes? K, you\u2019re still in. 3 strikes? Nah, you\u2019re pump membrane with ATP site on cytosolic side. For out! each ATP consumed, 2 K+ go in to the cell Digoxin directly inhibits Na+\/K+-ATPase \u008e (pump dephosphorylated) and 3 Na+ go out of indirect inhibition of Na+\/Ca2+ exchange \u008e the cell (pump phosphorylated). \u008f\u00a0[Ca2+]i \u008e \u008f\u00a0cardiac contractility. Extracellular 3Na+ 2K+ space 3Na+ P P 2K+ Plasma ATP membrane ADP Cytosol uploaded by medbooksvn","48 SEC TION II Biochemistry\u2003 \uf07d\u2009BIOCHEMISTRY\u2014Cellular Collagen Most abundant protein in the human body. Type I - Skeleton Extensively modified by posttranslational Type II - Cartilage Type I Type III - Arteries Type II modification. Type IV - Basement membrane Type III Organizes and strengthens extracellular matrix. SCAB Type IV Types I to IV are the most common types in Type I: bone, tendone. humans. \u0090 production in osteogenesis imperfecta type I. Most common (90%)\u2014Bone (made by Type II: cartwolage. osteoblasts), Skin, Tendon, dentin, fascia, cornea, late wound repair. Type III: deficient in vascular type of Ehlers- Danlos syndrome (threE D). Cartilage (including hyaline), vitreous body, nucleus pulposus. Type IV: under the floor (basement membrane). Defective in Alport syndrome; targeted by Reticulin\u2014skin, blood vessels, uterus, fetal tissue, early wound repair. autoantibodies in Goodpasture syndrome. Myofibroblasts are responsible for secretion Basement membrane\/basal lamina (glomerulus, cochlea), lens. (proliferative stage) and wound contraction. Collagen synthesis and structure Fibroblast Preprocollagen S\u0007 ynthesis\u2014translation of collagen \u03b1 chains (preprocollagen)\u2014usually Gly-X-Y Nucleus OH OH Pro \u03b1-chain backbone (Gly-X-Y) (X is often proline or lysine and Y is often Sugar Hydroxylation of proline and hydroxyproline or hydroxylysine). Collagen is Collagen mRNA lysine (requires vitamin C) 1\/3 glycine; glycine content of collagen is less OH OH Glycosylation variable than that of lysine and proline. Cytoplasm H\u0007 ydroxylation\u2014hydroxylation RER Procollagen Triple helix formation (\u201chydroxCylation\u201d) of specific proline and lysine residues. Requires vitamin C; Golgi deficiency \u008e\u00a0scurvy. \u0007Glycosylation\u2014glycosylation of pro-\u03b1-chain Extracellular Exocytosis hydroxylysine residues and formation of space procollagen via hydrogen and disulfide bonds Cleavage of procollagen (triple helix of 3 collagen \u03b1 chains). Problems C- and N-terminals forming triple helix \u008e\u00a0osteogenesis imperfecta. Tropocollagen E\u0007 xocytosis\u2014exocytosis of procollagen into extracellular space. Self assembly into P\u0007 roteolytic processing\u2014cleavage of collagen \ufb01brils disulfide-rich terminal regions of procollagen \u008e\u00a0insoluble tropocollagen. Formation of cross-links \u0007Assembly and alignment\u2014collagen assembles (stabilized by lysyl oxidase) in fibrils and aligns for cross-linking. C\u0007 ross-linking\u2014reinforcement of staggered Collagen \ufb01ber tropocollagen molecules by covalent lysine- hydroxylysine cross-linkage (by copper- containing lysyl oxidase) to make collagen fibers. Cross-linking of collagen \u008f with age. Problems with cross-linking \u008e\u00a0Menkes disease.","Biochemistry\u2003 \uf07d\u2009BIOCHEMISTRY\u2014Cellular SEC TION II 49 Osteogenesis Genetic bone disorder (brittle bone May be confused with child abuse. imperfecta disease) caused by a variety of gene defects Treat with bisphosphonates to \u0090\u00a0fracture risk. A (most commonly COL1A1 and COL1A2). Patients can\u2019t BITE: Bones = multiple fractures Upper Most common form is autosomal dominant I (eye) = blue sclerae extremity with \u0090 production of otherwise normal type\u00a0I Teeth = dental imperfections collagen (altered triple helix formation). Ear = hearing loss Ehlers-Danlos Manifestations include: syndrome \u0083\t Multiple fractures and bone deformities B (arrows in A ) after minimal trauma (eg, Menkes disease during birth) \u0083\t Blue sclerae B due to the translucent connective tissue over choroidal veins \u0083\t Some forms have tooth abnormalities, including opalescent teeth that wear easily due to lack of dentin (dentinogenesis imperfecta) \u0083\t Conductive hearing loss (abnormal ossicles) Faulty collagen synthesis causing A B hyperextensible skin A , hypermobile joints B , and tendency to bleed (easy bruising). Multiple types. Inheritance and severity vary. Can be autosomal dominant or recessive. May be associated with joint dislocation, berry and aortic aneurysms, organ rupture. Hypermobility type (joint instability): most common type. Classical type (joint and skin symptoms): caused by a mutation in type V collagen (eg, COL5A1, COL5A2). Vascular type (fragile tissues including vessels [eg, aorta], muscles, and organs that are prone to rupture [eg, gravid uterus]): mutations in type III procollagen (eg, COL3A1). Can be caused by procollagen peptidase deficiency. X-linked recessive connective tissue disease caused by impaired copper absorption and transport due to defective Menkes protein ATP7A (Absent copper), vs ATP7B in Wilson disease (copper Buildup). Leads to \u0090 activity of lysyl oxidase (copper is a necessary cofactor) \u008e defective collagen cross-linking. Results in brittle, \u201ckinky\u201d hair, growth and developmental delay, hypotonia, \u008f\u00a0risk of cerebral aneurysms. uploaded by medbooksvn","50 SEC TION II Biochemistry\u2003 \uf07d\u2009Biochemistry\u2014Laboratory Techniques Elastin Stretchy protein within skin, lungs, large arteries, elastic ligaments, vocal cords, epiglottis, ligamenta flava (connect vertebrae \u008e relaxed and stretched conformations). Single Rich in nonhydroxylated proline, glycine, and lysine residues, vs the hydroxylated residues of elastin Stretch Relax Cross-link collagen. molecule Tropoelastin with fibrillin scaffolding. Cross-linking occurs extracellularly via lysyl oxidase and gives elastin its elastic properties. Broken down by elastase, which is normally inhibited by \u03b11-antitrypsin. \u03b11-Antitrypsin deficiency results in unopposed elastase activity, which can cause COPD. A Marfan syndrome\u2014autosomal dominant (with variable expression) connective tissue disorder affecting skeleton, heart, and eyes. FBN1 gene mutation on chromosome 15 (fifteen) results in defective fibrillin-1, a glycoprotein that forms a sheath around elastin and sequesters TGF-\u03b2. Findings: tall with long extremities; chest wall deformity (pectus carinatum [pigeon chest] or pectus excavatum A ); hypermobile joints; long, tapering fingers and toes (arachnodactyly); cystic medial necrosis of aorta; aortic root aneurysm rupture or dissection (most common cause of death); mitral valve prolapse; \u008f\u00a0risk of spontaneous pneumothorax. Homocystinuria\u2014most commonly due to cystathionine synthase deficiency leading to homocysteine buildup. Presentation similar to Marfan syndrome with pectus deformity, tall stature, \u008f\u00a0arm:height ratio, \u0090\u00a0upper:lower body segment ratio, arachnodactyly, joint hyperlaxity, skin hyperelasticity, scoliosis, fair complexion (vs Marfan syndrome). Marfan syndrome Homocystinuria INHERITANCE Autosomal dominant Autosomal recessive INTELLECT Normal Decreased VASCULAR COMPLICATIONS Aortic root dilatation Thrombosis LENS DISLOCATION Upward\/temporal (Marfan fans out) Downward\/nasal `\u2009BIOCHEMISTRY\u2014LABORATORY TECHNIQUES Polymerase chain Molecular biology lab procedure used to amplify a desired fragment of DNA. Useful as a diagnostic reaction tool (eg, neonatal HIV, herpes encephalitis). 5' 3' 5' 3' 5' 3' 5' 3' DNA primer 3' 5' 3' 3' 5' dNTP Repeat Double-stranded DNA 5' 3' 5' 3' 5' 3' 5' \u2002 \u0007Denaturation\u2014DNA template, DNA primers, a heat-stable DNA polymerase, and deoxynucleotide triphosphates (dNTPs) are heated to ~ 95\u00baC to separate the DNA strands. \u2002 \u0007Annealing\u2014sample is cooled to ~ 55\u00baC. DNA primers anneal to the specific sequence to be amplified on the DNA template. \u2002 \u0007Elongation\u2014temperature is increased to ~ 72\u00baC. DNA polymerase adds dNTPs to the strand to replicate the sequence after each primer. Heating and cooling cycles continue until the amount of DNA is sufficient.","Biochemistry\u2003 \uf07d\u2009Biochemistry\u2014Laboratory Techniques SEC TION II 51 CRISPR\/Cas9 A genome editing tool derived from bacteria. Consists of a guide RNA (gRNA) , which is complementary to a target DNA sequence, and an endonuclease (Cas9), which makes a single- or double-strand break at the target site . Imperfectly cut segments are repaired by nonhomologous end joining (NHEJ) \u008e accidental frameshift mutations (\u201cknock-out\u201d) , or a donor DNA sequence can be added to fill in the gap using homology-directed repair (HDR) . Potential applications include removing virulence factors from pathogens, replacing disease-causing alleles of genes with healthy variants (in clinical trials for sickle cell disease), and specifically targeting tumor cells. Cas9 gRNA NHEJ 3A 3B HDR + Donor DNA Frameshift\/inactivation Edited sequence (\u201dknock-out\u201d) (\u201dknock-in\u201d) Blotting procedures 1.\u2002DNA sample is enzymatically cleaved into I: Parents Southern blot smaller pieces, which are separated by gel PEDIGREE Northern blot electrophoresis, and then transferred to a Western blot Southwestern blot membrane. II: Children 2.\u2002 Membrane is exposed to labeled DNA probe that anneals to its complementary strand. Aa Aa aa Aa AA Genotype 3.\u2002 Resulting double-stranded, labeled piece SOUTHERN BLOT of DNA is visualized when membrane is Mutant exposed to film or digital imager. Normal Useful to identify size of specific sequences (eg, determination of heterozygosity [as seen SNoW DRoP: in image], # of CGG repeats in FMR1 to diagnose Fragile X syndrome) Southern = DNA Northern = RNA Western = Protein Similar to Southern blot, except that an RNA sample is electrophoresed. Useful for studying mRNA levels and size, which are reflective of gene expression. Detects splicing errors. Sample protein is separated via gel electrophoresis and transferred to a membrane. Labeled antibody is used to bind relevant protein. This helps identify specific protein and determines quantity. Identifies DNA-binding proteins (eg, c-Jun, c-Fos [leucine zipper motif]) using labeled double- stranded DNA probes. Southern (DNA) + Western (protein) = Southwestern (DNA-binding protein). uploaded by medbooksvn","52 SEC TION II Biochemistry\u2003 \uf07d\u2009Biochemistry\u2014Laboratory Techniques Flow cytometry Laboratory technique to assess size, granularity, Fluorescent and protein expression (immunophenotype) of label individual cells in a sample. CD3 Cell Laser Antibody Detector Laser makes Cells are tagged with antibodies specific to label \ufb02uoresce surface or intracellular proteins. Antibodies Anti-CD3 Ab 101 102 are then tagged with a unique fluorescent CD8 103 104 dye. Sample is analyzed one cell at a time by Anti-CD8 Ab focusing a laser on the cell and measuring Fluorescence light scatter and intensity of fluorescence. is detected; Data are plotted either as histogram (one labeled cells measure) or scatter plot (any two measures, as are counted shown). In illustration: \u0083\t Cells in left lower quadrant \u229d for both CD8 104 and CD3. \u0083\t Cells in right lower quadrant \u2295 for CD8 103 and \u229d for CD3. In this example, right lower quadrant is empty because all 102 CD8-expressing cells also express CD3. \u0083\t Cells in left upper quadrant \u2295 for CD3 and 101 \u229d for CD8. \u0083\t Cells in right upper quadrant \u2295 for both 100 CD8 and CD3. 100 Commonly used in workup of hematologic abnormalities (eg, leukemia, paroxysmal nocturnal hemoglobinuria, fetal RBCs in pregnant person\u2019s blood) and immunodeficiencies (eg, CD4+ cell count in HIV). Microarrays Array consisting of thousands of DNA oligonucleotides arranged in a grid on a glass or silicon chip. The DNA or RNA samples being compared are attached to different fluorophores and hybridized to the array. The ratio of fluorescence signal at a particular oligonucleotide reflects the relative amount of the hybridizing nucleic acid in the two samples. Used to compare the relative transcription of genes in two RNA samples. Can detect single nucleotide polymorphisms (SNPs) and copy number variants (CNVs) for genotyping, clinical genetic testing, forensic analysis, and cancer mutation and genetic linkage analysis when DNA is used. Enzyme-linked Immunologic test used to detect the presence Direct ELISA Substrate immunosorbent assay of either a specific antigen or antibody in a patient\u2019s blood sample. Detection involves Enzyme the use of an antibody linked to an enzyme. Added substrate reacts with the enzyme, Labeled 1\u00b0 antibody Detectable producing a detectable signal. Can have high signal sensitivity and specificity, but is less specific than Western blot. Often used to screen for Antigen Substrate HIV infection. Indirect ELISA Labeled 2\u00b0 antibody 1\u00b0 antibody Antigen","Biochemistry\u2003 \uf07d\u2009Biochemistry\u2014Laboratory Techniques SEC TION II 53 Karyotyping Colchicine is added to cultured cells to halt A chromosomes in metaphase. Chromosomes are stained, ordered, and numbered according to morphology, size, arm-length ratio, and banding pattern (arrows in A point to extensive abnormalities in a cancer cell). Can be performed on a sample of blood, bone marrow, amniotic fluid, or placental tissue. Used to diagnose chromosomal imbalances (eg, autosomal trisomies, sex chromosome disorders). Fluorescence in situ Fluorescent DNA or RNA probe binds to A hybridization specific gene or other site of interest on chromosomes. Used for specific localization of genes and direct visualization of chromosomal anomalies. \u0083\t Microdeletion\u2014no fluorescence on a chromosome compared to fluorescence at the same locus on the second copy of that chromosome. \u0083\t Translocation\u2014 A fluorescence signal (from ABL gene) that corresponds to one chromosome (chromosome 9) is found in a different chromosome (chromosome 22, next to BCR gene). \u0083\t Duplication\u2014a second copy of a chromosome, resulting in a trisomy or tetrasomy. Molecular cloning Production of a recombinant DNA molecule in a bacterial host. Useful for production of human proteins in bacteria (eg, human growth hormone, insulin). Steps: 1.\u2002 Isolate eukaryotic mRNA (post-RNA processing) of interest. 2.\u2002 Add reverse transcriptase (an RNA-dependent DNA polymerase) to produce complementary DNA (cDNA, lacks introns). 3.\u2002 Insert cDNA fragments into bacterial plasmids containing antibiotic resistance genes. 4.\u2002 Transform (insert) recombinant plasmid into bacteria. 5.\u2002 Surviving bacteria on antibiotic medium produce cloned DNA (copies of cDNA). uploaded by medbooksvn","54 SEC TION II Biochemistry\u2003 \uf07d\u2009BIOCHEMISTRY\u2014Genetics Gene expression Transgenic strategies in mice involve: Knock-out = removing a gene, taking it out. modifi ations \u0083\t Random insertion of gene into mouse Knock-in = inserting a gene. genome RNA interference \u0083\t Targeted insertion or deletion of gene Random insertion\u2014constitutive expression. MicroRNA through homologous recombination with Targeted insertion\u2014conditional expression. mouse gene Small interfering RNA Process whereby small non-coding RNA molecules target mRNAs to inhibit gene expression. Naturally produced by cell as hairpin structures. Abnormal expression of miRNAs contributes Loose nucleotide pairing allows broad to certain malignancies (eg, by silencing an targeting of related mRNAs. When miRNA mRNA from a tumor suppressor gene). binds to mRNA, it blocks translation of mRNA and sometimes facilitates its degradation. Usually derived from exogenous dsRNA source Can be produced by transcription or (eg, virus). Once inside a cell, siRNA requires chemically synthesized for gene \u201cknockdown\u201d complete nucleotide pairing, leading to highly experiments. specific mRNA targeting. Results in mRNA cleavage prior to translation. ` \u2009B I O C H E M I S T R Y \u2014 G E N E T I C S Genetic terms DEFINITION EXAMPLE TERM Both alleles contribute to the phenotype of the Blood groups A, B, AB; \u03b11-antitrypsin heterozygote. deficiency; HLA groups. Codominance Variable expressivity Patients with the same genotype have varying Two patients with neurofibromatosis type 1 (NF1) Incomplete phenotypes. may have varying disease severity. penetrance Not all individuals with a disease show the BRCA1 gene mutations do not always result in Pleiotropy disease. breast or ovarian cancer. Anticipation Loss of heterozygosity % penetrance \u00d7 probability of inheriting Untreated phenylketonuria (PKU) manifests with genotype = risk of expressing phenotype. light skin, intellectual disability, musty body odor. Epistasis Aneuploidy One gene contributes to multiple phenotypic Trinucleotide repeat diseases (eg, Huntington effects. disease). Increased severity or earlier onset of disease in Retinoblastoma and the \u201ctwo-hit hypothesis,\u201d succeeding generations. Lynch syndrome (HNPCC), Li-Fraumeni syndrome. If a patient inherits or develops a mutation in a tumor suppressor gene, the wild type allele Albinism, alopecia. must be deleted\/mutated\/eliminated before cancer develops. This is not true of oncogenes. Down syndrome, Turner syndrome, oncogenesis. The allele of one gene affects the phenotypic expression of alleles in another gene. An abnormal number of chromosomes; due to chromosomal nondisjunction during mitosis or meiosis.","Biochemistry\u2003 \uf07d\u2009BIOCHEMISTRY\u2014Genetics SEC TION II 55 Genetic terms (continued) TERM DEFINITION EXAMPLE Dominant negative Exerts a dominant effect. A heterozygote A single mutated p53 tumor suppressor gene mutation produces a nonfunctional altered protein that results in a protein that is able to bind DNA also prevents the normal gene product from and block the wild type p53 from binding to the functioning. promoter. Linkage Tendency for certain alleles to occur in close McCune-Albright syndrome\u2014due to Gs-protein disequilibrium proximity on the same chromosome more or activating mutation. Presents with unilateral less often than expected by chance. Measured caf\u00e9-au-lait spots A with ragged edges, in a population, not in a family, and often polyostotic fibrous dysplasia (bone is replaced varies in different populations. by collagen and fibroblasts), and at least one endocrinopathy (eg, precocious puberty). Mosaicism Presence of genetically distinct cell lines in the Lethal if mutation occurs before fertilization A same individual. (affecting all cells), but survivable in patients with mosaicism. Somatic mosaicism\u2014mutation arises from mitotic errors after fertilization and propagates Albinism, retinitis pigmentosa, familial through multiple tissues or organs. hypercholesteremia. Germline (gonadal) mosaicism\u2014mutation only \u03b2-thalassemia. in egg or sperm cells. If parents and relatives do not have the disease, suspect gonadal (or mtDNA passed from mother to all children. germline) mosaicism. Uniparental is euploid (correct number of Locus heterogeneity Mutations at different loci result in the same chromosomes). Most occurrences of uniparental disease. disomy (UPD) \u008e normal phenotype. Consider isodisomy in an individual manifesting a Allelic heterogeneity Different mutations in the same locus result\u00a0in recessive disorder when only one parent is a the same disease. carrier. Examples: Prader-Willi and Angelman syndromes. Heteroplasmy Presence of both normal and mutated mtDNA, resulting in variable expression in mitochondrially inherited disease. Uniparental disomy Offspring receives 2 copies of a chromosome from 1 parent and no copies from the other parent. HeterodIsomy (heterozygous) indicates a meiosis I error. IsodIsomy (homozygous) indicates a meiosis II error or postzygotic chromosomal duplication of one of a pair of chromosomes, and loss of the other of the original pair. Population genetics DESCRIPTION EXAMPLE CONCEPT Fitness equal across alleles \u008e natural disaster that The founder effect is a type of bottleneck removes certain alleles by chance \u008e new allelic when cause is due to calamitous population Bottleneck effect frequency (by chance, not naturally selected). separation. Natural selection Alleles that increase species fitness are more likely Human evolution. to be passed down to offspring and vice versa. Genetic drift Founder effect and bottleneck effect are both Also called allelic drift or Wright effect. A examples of genetic drift. dramatic shift in allelic frequency that occurs by change (not by natural selection). uploaded by medbooksvn","56 SEC TION II Biochemistry\u2003 \uf07d\u2009BIOCHEMISTRY\u2014Genetics Hardy-Weinberg In a given population where mating is at If a population is in Hardy-Weinberg principle equilibrium, then the values of p and q remain random, allele and genotype frequencies constant from generation to generation. A (p) a (q) will be constant. If p and q represent the In rare autosomal recessive diseases, p \u2248 1. A (p) AA Aa frequencies of alleles A and a in a population, Example: The prevalence of cystic fibrosis (p ) (pq) respectively, then p + q = 1, where: \u0083\t p2 = frequency of homozygosity for allele A (an autosomal recessive disease) in the US a (q) Aa aa \u0083\t q2 = frequency of homozygosity for allele a is approximately 1\/3200, which tells us that (pq) (q ) \u0083\t 2pq = frequency of heterozygosity (carrier q2 = 1\/3200, with q \u2248 0.017 or 1.7% of the population. Since p + q = 1, we know that frequency, if an autosomal recessive disease) p = 1 \u2013 \u221a1\/3200 \u2248 0.982, which gives us a heterozygous carrier frequency of 2pq = 0.035 Therefore the sum of the frequencies of these or 3.5% of the population. Notice that since genotypes is p2 + 2pq + q2 = 1. the disease is relatively rare, we could have approximated p \u2248 1 and obtained a similar The frequency of an X-linked recessive disease result. in males = q and in females = q2. Hardy-Weinberg law assumptions include: \u0083\t No mutation occurring at the locus \u0083\t Natural selection is not occurring \u0083\t Completely random mating \u0083\t N\u0007 o net migration \u0083\t Large population Disorders of imprinting One gene copy is silenced by methylation, and only the other copy is expressed \u008e\u00a0parent-of-origin effects. The expressed copy may be mutated, may not be expressed, or may be deleted altogether. Prader-Willi syndrome Angelman syndrome WHICH GENE IS SILENT? Maternally derived genes are silenced Paternally derived UBE3A is silenced Disease occurs when the paternal allele is deleted Disease occurs when the maternal allele is or mutated deleted or mutated SIGNS AND SYMPTOMS Hyperphagia, obesity, intellectual disability, Hand-flapping, Ataxia, severe Intellectual hypogonadism, hypotonia disability, inappropriate Laughter, Seizures. HAILS the Angels. CHROMOSOMES INVOLVED Chromosome 15 of paternal origin UBE3A on maternal copy of chromosome 15 NOTES 25% of cases are due to maternal uniparental 5% of cases are due to paternal uniparental disomy disomy POP: Prader-Willi, Obesity\/overeating, Paternal MAMAS: Maternal allele deleted, Angelman allele deleted syndrome, Mood, Ataxia, Seizures Normal Mutation P = Paternal PM PM M = Maternal Active gene Silenced gene (imprinting) Gene deletion\/mutation Prader-Willi syndrome Angelman syndrome","Biochemistry\u2003 \uf07d\u2009BIOCHEMISTRY\u2014Genetics SEC TION II 57 Modes of inheritance Often due to defects in structural genes. Many Often pleiotropic (multiple apparently unrelated Autosomal dominant generations, both males and females are affected. effects) and variably expressive (different between individuals). Family history crucial Aa to diagnosis. With one affected (heterozygous) parent, each child has a 50% chance of being a Aa aa affected. a Aa aa Autosomal recessive With 2 carrier (heterozygous) parents, on average: Often due to enzyme deficiencies. Usually seen each child has a 25% chance of being affected, in only 1 generation. Commonly more severe 50% chance of being a carrier, and 25% chance than dominant disorders; patients often present of not being affected nor a carrier. in childhood. Aa \u008f risk in consanguineous families. Unaffected individual with affected sibling has A AA Aa 2\/3 probability of being a carrier. a Aa aa X-linked recessive Sons of heterozygous mothers have a 50% Commonly more severe in males. Females chance of being affected. No male-to-male usually must be homozygous to be affected. carrier transmission. Skips generations. XX XX X XX XX X XX XX Y XY XY Y XY XY X-linked dominant Transmitted through both parents. Children of Examples: fragile X syndrome, Alport syndrome, affected mothers each have a 50% chance of hypophosphatemic rickets (also called X-linked being affected. 100% of daughters and 0% of hypophosphatemia)\u2014phosphate wasting at sons of affected fathers will be affected. proximal tubule \u008e\u00a0ricketslike presentation. XX XX X XX XX X XX XX Y XY XY Y XY XY Mitochondrial Transmitted only through the mother. All Caused by mutations in mtDNA. inheritance offspring of affected females may show signs of Examples: mitochondrial myopathies, Leber disease. hereditary optic neuropathy. Variable expression in a population or even within a family due to heteroplasmy. = una ected male; = a ected male; = una ected female; = a ected female. uploaded by medbooksvn","58 SEC TION II Biochemistry\u2003 \uf07d\u2009BIOCHEMISTRY\u2014Genetics Autosomal dominant Achondroplasia, autosomal dominant polycystic kidney disease, familial adenomatous polyposis, diseases familial hypercholesterolemia, hereditary hemorrhagic telangiectasia (Osler-Weber-Rendu syndrome), hereditary spherocytosis, Huntington disease, Li-Fraumeni syndrome, Marfan syndrome, multiple endocrine neoplasias, myotonic muscular dystrophy, neurofibromatosis type 1 (von Recklinghausen disease), neurofibromatosis type 2, tuberous sclerosis, von Hippel-Lindau disease. Autosomal recessive Mostly consist of enzyme defects. Oculocutaneous albinism, phenylketonuria, cystic fibrosis, sickle diseases cell disease, Wilson disease, sphingolipidoses (except Fabry disease), hemochromatosis, glycogen storage diseases, thalassemia, mucopolysaccharidoses (except Hunter syndrome), Friedreich ataxia, Kartagener syndrome, ARPKD. Oh, please! Can students who score high grades tell me features of the kidney disorder Autosomal Recessive Polycystic Kidney Disease? Cystic fib osis Autosomal recessive; defect in CFTR gene on chromosome 7 (deletion; \u0394F508). Most common lethal genetic disease in patients with European ancestry. GENETICS PATHOPHYSIOLOGY CFTR encodes an ATP-gated Cl\u2212 channel (secretes Cl\u2212 in lungs\/GI tract, reabsorbs Cl\u2212 in sweat glands). Phe508 deletion \u008e\u00a0misfolded protein \u008e\u00a0improper protein trafficking \u008e\u00a0protein absent DIAGNOSIS from cell membrane \u008e\u00a0\u0090\u00a0Cl\u2212 (and H2O) secretion \u008e\u00a0compensatory \u008f\u00a0Na+ reabsorption via COMPLICATIONS epithelial Na+ channels (ENaC) \u008e\u00a0\u008f\u00a0H2O reabsorption \u008e\u00a0abnormally thick mucus secreted into lungs\/GI tract. \u008f\u00a0Na+ reabsorption = more negative transepithelial potential difference. TREATMENT \u008f Cl\u2212 concentration in pilocarpine-induced sweat test. Can present with contraction alkalosis and hypokalemia (ECF effects analogous loop diuretic effect) due to ECF H2O\/Na+ losses via sweating and concomitant renal K+\/H+ wasting. \u008f\u00a0immunoreactive trypsinogen (newborn screening) due to clogging of pancreatic duct. Recurrent pulmonary infections (eg, S aureus [infancy and early childhood], P aeruginosa [adulthood], allergic bronchopulmonary aspergillosis [ABPA]), chronic bronchitis and bronchiectasis \u008e\u00a0reticulonodular pattern on CXR, opacification of sinuses. Nasal polyps, nail clubbing. Pancreatic insufficiency, malabsorption with steatorrhea, and fat-soluble vitamin deficiencies (A, D, E, K) progressing to endocrine dysfunction (CF-related diabetes), biliary cirrhosis, liver disease. Meconium ileus in newborns. Infertility in males (absence of vas deferens, spermatogenesis may be unaffected) and subfertility in females (amenorrhea, abnormally thick cervical mucus). Multifactorial: chest physiotherapy, aerosolized dornase alfa (DNase), and inhaled hypertonic saline \u008e\u00a0mucus clearance. Azithromycin prevents acute exacerbations. Ibuprofen for anti-inflammatory effect. Pancreatic enzyme replacement therapy (pancrelipase) for pancreatic insufficiency. CFTR modulators can be used alone or in combination. Efficacy varies by different genetic mutations (pharmacogenomics). Are either potentiators (hold gate of CFTR channel open \u008e\u00a0Cl\u2212 flows through cell membrane; eg, ivacaftor) or correctors (help CFTR protein to form right 3-D shape \u008e\u00a0moves to the cell surface; eg, lumacaftor, tezacaftor). CI\u2013 Na+ CI\u2013 Na+ Normal mucus Dehydrated mucus CFTR ENaC CI\u2013 H\u2082O Na+ Lumen Normal CI\u2013 H\u2082O Na+ Normal Sweat duct CF Airway CF Interstitium","Biochemistry\u2003 \uf07d\u2009BIOCHEMISTRY\u2014Genetics SEC TION II 59 X-linked recessive Bruton agammaglobulinemia, Duchenne and Becker muscular dystrophies, Fabry disease, G6PD diseases deficiency, hemophilia A and B, Hunter syndrome, Lesch-Nyhan syndrome, ocular albinism, ornithine transcarbamylase (OTC) deficiency, Wiskott-Aldrich syndrome. Females with Turner syndrome (45,XO) are more likely to have an X-linked recessive disorder. X-inactivation (lyonization)\u2014during development, one of the X chromosomes in each XX cell is randomly deactivated and condensed into a Barr body (methylated heterochromatin). If skewed inactivation occurs, XX individuals may express X-linked recessive diseases (eg, G6PD); penetrance and severity of X-linked dominant diseases in XX individuals may also be impacted. Muscular dystrophies X-linked recessive disorder typically due to Duchenne = deleted dystrophin. Duchenne frameshift deletions or nonsense mutations Dystrophin gene (DMD) is the largest A \u008e truncated or absent dystrophin protein \u008e\u00a0progressive myofiber damage. Can also protein-coding human gene \u008e \u008f\u00a0chance of Muscle fibers result from splicing errors. spontaneous mutation. Dystrophin helps to anchor muscle fibers to the extracellular Becker Weakness begins in pelvic girdle muscles and matrix, primarily in skeletal and cardiac Myotonic dystrophy progresses superiorly. Pseudohypertrophy of muscles. Loss of dystrophin \u008e\u00a0myonecrosis. calf muscles due to fibrofatty replacement of \u008f\u00a0CK and aldolase; genetic testing confirms muscle A . Waddling gait. diagnosis. Onset before 5 years of age. Dilated Calf cardiomyopathy is common cause of death. pseudohypertrophy Gowers sign\u2014patient uses upper extremities to Lordosis help stand up. Classically seen in Duchenne muscular dystrophy, but also seen in other Thigh muscular dystrophies and inflammatory atrophy myopathies (eg, polymyositis). Pushing on leg X-linked recessive disorder typically due to to stand non-frameshift deletions in dystrophin gene (partially functional instead of truncated). Deletions can cause both Duchenne and Less severe than Duchenne (Becker is better). Becker muscular dystrophies. 2\u20443 of cases have Onset in adolescence or early adulthood. large deletions spanning one or more exons. Autosomal dominant. Onset 20\u201330 years. CTG Cataracts, Toupee (early balding in males), trinucleotide repeat expansion in the DMPK Gonadal atrophy. gene \u008e\u00a0abnormal expression of myotonin protein kinase \u008e\u00a0myotonia (eg, difficulty releasing hand from handshake), muscle wasting, cataracts, testicular atrophy, frontal balding, arrhythmia. uploaded by medbooksvn","60 SEC TION II Biochemistry\u2003 \uf07d\u2009BIOCHEMISTRY\u2014Genetics Mitochondrial diseases Rare disorders arising 2\u00b0 to failure in oxidative phosphorylation. Tissues with \u008f energy requirements are preferentially affected (eg, CNS, skeletal muscle). Mitochondrial myopathies\u2014include MELAS (mitochondrial encephalomyopathy with lactic acidosis and strokelike episodes) and MERRF (myoclonic epilepsy with ragged red fibers). Light microscopy with stain: ragged red fibers due to compensatory proliferation of mitochondria. Electron microscopy: mitochondrial crystalline inclusions. Leber hereditary optic neuropathy\u2014mutations in complex I of ETC \u008e neuronal death in retina and optic nerve \u008e subacute bilateral vision loss in teens\/young adults (males > females). Usually permanent. May be accompanied by neurologic dysfunction (eg, tremors, multiple sclerosis\u2013like illness). Rett syndrome Sporadic disorder caused by de novo mutation of MECP2 on X chromosome. Seen mostly in Fragile X syndrome females. Embryonically lethal in males. Individuals with Rett syndrome experience initial normal development (6\u201318 months) followed by regression (\u201cretturn\u201d) in motor, verbal, and cognitive abilities; ataxia; seizures; scoliosis; and stereotypic hand-wringing. X-linked dominant inheritance. Trinucleotide Trinucleotide repeat expansion [(CGG)n] occurs repeats in FMR1 \u008e\u00a0hypermethylation of during oogenesis. cytosine residues \u008e\u00a0\u0090\u00a0expression. Premutation (50\u2013200 repeats) \u008e\u00a0tremor, ataxia, Most common inherited cause of intellectual 1\u00b0 ovarian insufficiency. disability (Down syndrome is most common genetic cause, but most cases occur Full mutation (>200 repeats) \u008e\u00a0postpubertal sporadically). macroorchidism (enlarged testes), long face with large jaw, large everted ears, autism, mitral valve prolapse, hypermobile joints. Self-mutilation is common and can be confused with Lesch-Nyhan syndrome. Trinucleotide repeat May show genetic anticipation (disease severity \u008f\u00a0and age of onset \u0090\u00a0in successive generations). expansion diseases TRINUCLEOTIDE REPEAT MODE OF INHERITANCE MNEMONIC DISEASE (CAG)n AD Caudate has \u0090\u00a0ACh and GABA Huntington disease (CTG)n AD Myotonic dystrophy Cataracts, Toupee (early balding in males), (CGG)n XD Gonadal atrophy in males, reduced fertility in Fragile X syndrome (GAA)n AR females Friedreich ataxia Chin (protruding), Giant Gonads Ataxic GAAit","Biochemistry\u2003 \uf07d\u2009BIOCHEMISTRY\u2014Genetics SEC TION II 61 Autosomal trisomies Autosomal trisomies are screened in first and second trimesters with noninvasive prenatal tests. Down syndrome Incidence of trisomies: Down (21) > Edwards (18) > Patau (13). Autosomal monosomies are (trisomy 21) incompatible with life (high chance of recessive trait expression). Single palmar crease Findings: intellectual disability, flat facies, Drinking age (21). prominent epicanthal folds, single palmar Most common viable chromosomal disorder Edwards syndrome crease, incurved 5th finger, gap between 1st 2 (trisomy 18) toes, duodenal atresia, Hirschsprung disease, and most common cause of genetic congenital heart disease (eg, AVSD), Brushfield intellectual disability. Patau syndrome spots (whitish spots at the periphery of the iris). First-trimester ultrasound commonly shows (trisomy 13) Associated with early-onset Alzheimer disease \u008f\u00a0nuchal translucency and hypoplastic nasal (chromosome 21 codes for amyloid precursor bone. Markers for Down syndrome are hi up: protein), \u008f risk of AML\/ALL. \u008f hCG, \u008f inhibin. \u008f risk of umbilical hernia (incomplete closure of 95% of cases due to meiotic nondisjunction, umbilical ring). most commonly during meiosis I (\u008f\u00a0with The 5 A\u2019s of Down syndrome: advanced maternal age: from 1:1500 in females \u0083\t Advanced maternal age < 20 to 1:25 in females > 45). 4% of cases due to \u0083\t Atresia (duodenal) unbalanced Robertsonian translocation, most \u0083\t Atrioventricular septal defect typically between chromosomes 14 and 21. 1% \u0083\t Alzheimer disease (early onset) of cases due to postfertilization mitotic error. \u0083\t AML (<5 years of age)\/ALL (>5 years of age) Findings: PRINCE Edward\u2014Prominent Election age (18). occiput, Rocker-bottom feet, Intellectual 2nd most common autosomal trisomy resulting disability, Nondisjunction, Clenched fists with overlapping fingers, low-set Ears, micrognathia in live birth (most common is Down syndrome). (small jaw), congenital heart disease (eg, In Edwards syndrome, every prenatal screening VSD), omphalocele, myelomeningocele. marker decreases. Death usually occurs by age 1. Findings: severe intellectual disability, rocker- Puberty at age 13. bottom feet, microphthalmia, microcephaly, Defect in fusion of prechordal mesoderm cleft lip\/palate, holoprosencephaly, polydactyly, cutis aplasia, congenital heart \u008e\u00a0midline defects. (pump) disease, polycystic kidney disease, omphalocele. Death usually occurs by age 1. Cutis aplasia Nondisjunction in meiosis II 1st trimester screening Nondisjunction in meiosis I Meiosis I Trisomy \u03b2-hCG PAPP-A \u0090 Nondisjunction 21 \u008f \u0090 18 \u0090 \u0090 13 \u0090 Meiosis II 2nd trimester (quadruple) screening Nondisjunction Trisomy hCG Inhibin A Estriol AFP 21 \u008f \u008f \u0090 \u0090 Gametes 18 \u0090 \u2014 or \u0090 \u0090 \u0090 13 \u2014 \u2014 \u2014 \u2014 n+1 n+1 n\u20131 n\u20131 n n n\u20131 n+1 Normal Monosomy Trisomy Trisomy Monosomy uploaded by medbooksvn","62 SEC TION II Biochemistry\u2003 \uf07d\u2009BIOCHEMISTRY\u2014Genetics Genetic disorders by CHROMOSOME SELECTED EXAMPLES chromosome 3 von Hippel-Lindau disease, renal cell carcinoma 4 ADPKD (PKD2), achondroplasia, Huntington disease 5 Cri-du-chat syndrome, familial adenomatous polyposis 6 Hemochromatosis (HFE) 7 Williams syndrome, cystic fibrosis 9 Friedreich ataxia, tuberous sclerosis (TSC1) 11 Wilms tumor, \u03b2-globin gene defects (eg, sickle cell disease, \u03b2-thalassemia), MEN1 13 Patau syndrome, Wilson disease, retinoblastoma (RB1), BRCA2 15 Prader-Willi syndrome, Angelman syndrome, Marfan syndrome 16 ADPKD (PKD1), \u03b1-globin gene defects (eg, \u03b1-thalassemia), tuberous sclerosis (TSC2) 17 Neurofibromatosis type 1, BRCA1, TP53 (Li-Fraumeni syndrome) 18 Edwards syndrome 21 Down syndrome 22 Neurofibromatosis type 2, DiGeorge syndrome (22q11) X Fragile X syndrome, X-linked agammaglobulinemia, Klinefelter syndrome (XXY) Robertsonian Chromosomal translocation that commonly involves chromosome pairs 21, 22, 13, 14, and 15. translocation One of the most common types of translocation. Occurs when the long arms of 2 acrocentric chromosomes (chromosomes with centromeres near their ends) fuse at the centromere and the 2\u00a0short arms are lost. Balanced translocations (no gain or loss of significant genetic material) normally do not cause abnormal phenotype. Unbalanced translocations (missing or extra genes) can result in miscarriage, stillbirth, and chromosomal imbalance (eg, Down syndrome, Patau syndrome). Normal Robertsonian Unbalanced gamete gamete precursor translocation precursor Meiosis Meiosis Normal gamete Normal gamete Abnormal gametes Cri-du-chat syndrome Cri du chat = cry of the cat. Congenital deletion on short arm of chromosome 5 (46,XX or XY, 5p\u2212). Findings: microcephaly, moderate to severe intellectual disability, high-pitched crying, epicanthal folds, cardiac abnormalities (VSD). I cry when I am Very SaD.","Biochemistry\u2003 \uf07d\u2009BIOCHEMISTRY\u2014Nutrition SEC TION II 63 Williams syndrome Congenital microdeletion of long arm of chromosome 7 (deleted region includes elastin gene). Findings: distinctive \u201celfin\u201d facies, intellectual disability, hypercalcemia, well-developed verbal skills, extreme friendliness with strangers, cardiovascular problems (eg, supravalvular aortic stenosis, renal artery stenosis). ` \u2009B I O C H E M I S T R Y \u2014 N U T R I T I O N Essential fatty acids Polyunsaturated fatty acids that cannot be In contrast, consumption of trans-unsaturated synthesized in the body and must be provided fatty acids (found in fast food) promotes in the diet (eg, nuts\/seeds, plant oils, seafood). cardiovascular disease by \u008f LDL and \u0090 HDL. Linoleic acid (omega-6) is metabolized to arachidonic acid, which serves as the precursor to leukotrienes and prostaglandins. Linolenic acid (omega-3) and its metabolites have cardioprotective and antihyperlipidemic effects. Vitamins: fat soluble A, D, E, K. Absorption dependent on bile Malabsorption syndromes with steatorrhea (eg, emulsification, pancreatic secretions, and cystic fibrosis and celiac disease) or mineral intact ileum. Toxicity more common than oil intake can cause fat-soluble vitamin for water-soluble vitamins because fat-soluble deficiencies. vitamins accumulate in fat. Vitamins: water B1 (thiamine: TPP) Wash out easily from body except B12 and B9. soluble B2 (riboflavin: FAD, FMN) B12\u00a0stored in liver for ~ 3\u20134 years. B9 stored in B3 (niacin: NAD+) liver for ~ 3\u20134 months. B5 (pantothenic acid: CoA) B6 (pyridoxine: PLP) B-complex deficiencies often result in B7 (biotin) B9 (folate) dermatitis, glossitis, and diarrhea. B12 (cobalamin) C (ascorbic acid) Can be coenzymes (eg, ascorbic acid) or precursors to coenzymes (eg, FAD, NAD+). Dietary DIET SUPPLEMENTATION REQUIRED supplementation Vegetarian\/vegan Vitamin B12 Iron High egg white (raw) Vitamin B2 Untreated corn Frequently, vitamin D (although this is commonly deficient in many diets) Vitamin B7 (avidin in egg whites binds biotin and prevents absorption) Vitamin B3 (deficiency is common in resource-limited areas) uploaded by medbooksvn","64 SEC TION II Biochemistry\u2003 \uf07d\u2009BIOCHEMISTRY\u2014Nutrition Vitamin A Includes retinal, retinol, retinoic acid. Retinol is vitamin A, so think retin-A (used Antioxidant; constituent of visual pigments topically for wrinkles and Acne). FUNCTION (retinal); essential for normal differentiation Found in liver and leafy vegetables. DEFICIENCY of epithelial cells into specialized tissue Supplementation in vitamin A-deficient measles A (pancreatic cells, mucus-secreting cells); prevents squamous metaplasia. patients may improve outcomes. EXCESS Use oral isotretinoin to treat severe cystic acne. Night blindness (nyctalopia); dry, scaly skin Use all-trans retinoic acid to treat acute (xerosis cutis); dry eyes (xerophthalmia); conjunctival squamous metaplasia \u008e Bitot promyelocytic leukemia. spots (keratin debris; foamy appearance on conjunctiva A ); corneal degeneration (keratomalacia); immunosuppression. Acute toxicity\u2014nausea, vomiting, \u008f\u00a0ICP (eg, Teratogenic (interferes with homeobox gene; cleft vertigo, blurred vision). palate, cardiac abnormalities), therefore a \u229d pregnancy test and two forms of contraception Chronic toxicity\u2014alopecia, dry skin (eg, are required before isotretinoin (vitamin A scaliness), hepatic toxicity and enlargement, derivative) is prescribed. arthralgias, and idiopathic intracranial hypertension. Isotretinoin is teratogenic. Vitamin B1 Also called thiamine. FUNCTION In thiamine pyrophosphate (TPP), a cofactor for several dehydrogenase enzyme reactions (Be APT): \u0083\t Branched-chain ketoacid dehydrogenase DEFICIENCY \u0083\t \u03b1-Ketoglutarate dehydrogenase (TCA cycle) DISORDER \u0083\t Pyruvate dehydrogenase (links glycolysis to TCA cycle) \u0083\t Transketolase (HMP shunt) Wernicke encephalopathy Impaired glucose breakdown \u008e ATP depletion worsened by glucose infusion; highly aerobic tissues Korsakoff syndrome (eg, brain, heart) are affected first. In patients with chronic alcohol overuse or malnutrition, give Wernicke-Korsakoff thiamine before dextrose to \u0090\u00a0risk of precipitating Wernicke encephalopathy. syndrome Dry beriberi Diagnosis made by \u008f\u00a0in RBC transketolase activity following vitamin B1 administration. Wet beriberi CHARACTERISTICS Acute, reversible, life-threatening neurologic condition. Symptoms: Confusion, Ophthalmoplegia\/ Nystagmus, Ataxia (CorONA beer). Amnestic disorder due to chronic alcohol overuse; presents with confabulation, personality changes, memory loss (permanent). Damage to medial dorsal nucleus of thalamus, mammillary bodies. Presentation is combination of Wernicke encephalopathy and Korsakoff syndrome. Polyneuropathy, symmetric muscle wasting. Spell beriberi as Ber1Ber1 to remember vitamin\u00a0B1. High-output cardiac failure (due to systemic vasodilation).","Biochemistry\u2003 \uf07d\u2009BIOCHEMISTRY\u2014Nutrition SEC TION II 65 Vitamin B2 Also called riboflavin. FAD and FMN are derived from riboFlavin (B2 \u2248 2 ATP). FUNCTION Component of flavins FAD and FMN, used as DEFICIENCY cofactors in redox reactions, eg, the succinate The 2 C\u2019s of B2. dehydrogenase reaction in the TCA cycle. Vitamin B3 Cheilosis (inflammation of lips, scaling FUNCTION and fissures at the corners of the mouth), \u201cmagenta\u201d tongue, corneal vascularization. DEFICIENCY A Also called niacin, nicotinic acid. NAD derived from Niacin (B3 \u2248 3 ATP). EXCESS Constituent of NAD+, NADP+ (used in redox Hartnup disease\u2014autosomal recessive. reactions and as cofactor by dehydrogenases). Deficiency of neutral amino acid (eg, Vitamin B5 Derived from tryptophan. Synthesis requires tryptophan) transporters in proximal renal vitamins B2 and B6. Used to treat dyslipidemia tubular cells and on enterocytes \u008e\u00a0neutral FUNCTION (\u0090\u00a0VLDL, \u008f\u00a0HDL). aminoaciduria and \u0090\u00a0absorption from the DEFICIENCY gut \u008e\u00a0\u0090\u00a0tryptophan for conversion to niacin Glossitis. Severe deficiency of B3 leads to \u008e\u00a0pellagra-like symptoms. Treat with high- Vitamin B6 pellagra, which can also be caused by Hartnup protein diet and nicotinic acid. disease, malignant carcinoid syndrome FUNCTION (\u008f\u00a0tryptophan metabolism \u008e\u00a0\u008f\u00a0serotonin Pellagra = vitamin B3 levels fell. synthesis), and isoniazid (\u0090\u00a0vitamin B6). DEFICIENCY Symptoms of B3 deficiency (pellagra) (the 3 D\u2019s): diarrhea, dementia (also hallucinations), dermatitis (C3\/C4 dermatome circumferential \u201cbroad collar\u201d rash [Casal necklace], hyperpigmentation of sun-exposed limbs A ). Facial flushing (induced by prostaglandin, not Podagra = vitamin B3 OD (overdose). histamine; can avoid by taking aspirin before niacin), hyperglycemia, hyperuricemia. Also called pantothenic acid. B5 is \u201cpento\u201dthenic acid. Component of coenzyme A (CoA, a cofactor for acyl transfers) and fatty acid synthase. Dermatitis, enteritis, alopecia, adrenal insufficiency may lead to burning sensation of feet (\u201cburning feet syndrome\u201d; distal paresthesias, dysesthesia). Also called pyridoxine. Converted to pyridoxal phosphate (PLP), a cofactor used in transamination (eg, ALT and AST), decarboxylation reactions, glycogen phosphorylase. Synthesis of glutathione, cystathionine, heme, niacin, histamine, and neurotransmitters including serotonin, epinephrine, norepinephrine (NE), dopamine, and GABA. Convulsions, hyperirritability, peripheral neuropathy (deficiency inducible by isoniazid and oral contraceptives), sideroblastic anemia (due to impaired hemoglobin synthesis and iron excess). uploaded by medbooksvn","66 SEC TION II Biochemistry\u2003 \uf07d\u2009BIOCHEMISTRY\u2014Nutrition Vitamin B7 Also called biotin. FUNCTION Cofactor for carboxylation enzymes (which add a 1-carbon group): \u0083\t Pyruvate carboxylase (gluconeogenesis): pyruvate (3C) \u008e\u00a0oxaloacetate (4C) DEFICIENCY \u0083\t Acetyl-CoA carboxylase (fatty acid synthesis): acetyl-CoA (2C) \u008e\u00a0malonyl-CoA (3C) \u0083\t Propionyl-CoA carboxylase (fatty acid oxidation and branched-chain amino acid breakdown): Vitamin B9 propionyl-CoA (3C) \u008e\u00a0methylmalonyl-CoA (4C) FUNCTION Relatively rare. Dermatitis, enteritis, alopecia. Caused by long-term antibiotic use or excessive ingestion of raw egg whites. DEFICIENCY \u201cAvidin in egg whites avidly binds biotin.\u201d Also called folate. Found in leafy green vegetables. Also produced by gut microbiota. Folate absorbed in jejunum Converted to tetrahydrofolic acid (THF), a (think foliage in the \u201cjejun\u201dgle). coenzyme for 1-carbon transfer\/methylation reactions. Small reserve pool stored primarily in the liver. Important for the synthesis of nitrogenous bases Deficiency can be caused by several drugs (eg, in DNA and RNA. phenytoin, trimethoprim, methotrexate). Macrocytic, megaloblastic anemia; Supplemental folic acid at least 1 month prior hypersegmented polymorphonuclear cells to conception and during pregnancy to \u0090\u00a0risk (PMNs); glossitis; no neurologic symptoms (as of neural tube defects. Give vitamin B9 for the opposed to vitamin B12 deficiency). 9 months of pregnancy, and 1 month prior to conception. Labs: \u008f homocysteine, normal methylmalonic acid levels. Seen in chronic alcohol overuse and in pregnancy.","Biochemistry\u2003 \uf07d\u2009BIOCHEMISTRY\u2014Nutrition SEC TION II 67 Vitamin B12 Also called cobalamin. Found in animal products. Synthesized only FUNCTION Cofactor for methionine synthase (transfers by intestinal microbiota. Site of synthesis in DEFICIENCY CH3 groups as methylcobalamin) and methylmalonyl-CoA mutase. Important for humans is distal to site of absorption; thus B12 Vitamin C DNA synthesis. must be consumed via animal products. FUNCTION Macrocytic, megaloblastic anemia; Very large reserve pool (several years) stored DEFICIENCY hypersegmented PMNs; paresthesias EXCESS and subacute combined degeneration primarily in the liver. Deficiency caused (degeneration of dorsal columns, lateral corticospinal tracts, and spinocerebellar tracts) by malabsorption (eg, sprue, enteritis, due to abnormal myelin. Associated with \u008f\u00a0serum homocysteine and methylmalonic Diphyllobothrium latum, achlorhydria, acid levels, along with 2\u00b0 folate deficiency. Prolonged deficiency \u008e irreversible nerve bacterial overgrowth, alcohol overuse), lack of damage. intrinsic factor (eg, pernicious anemia, gastric bypass surgery), absence of terminal ileum (surgical resection, eg, for Crohn disease), certain drugs (eg, metformin), or insufficient intake (eg, veganism). B9 (folate) supplementation can mask the hematologic symptoms of B12 deficiency, but not the neurologic symptoms. Protein Fatty acids with odd number of Methionine carbons, branched-chain amino acids THF B12 Methionine synthase SAM THF\u2013CH3 Homocysteine CpaHt3htwoaaynsabolic Methylmalonyl-CoA B6 S-adenosyl B12 Methylmalonyl-CoA homocysteine mutase Cysteine Succinyl-CoA B6 Adenosine Heme TCA cycle Also called ascorbic acid. Found in fruits and vegetables. Pronounce \u201cabsorbic\u201d acid. Antioxidant; also facilitates iron absorption Ancillary treatment for methemoglobinemia by by reducing it to Fe2+ state. Necessary for hydroxylation of proline and lysine in reducing Fe3+ to Fe2+. collagen synthesis. Necessary for dopamine \u03b2-hydroxylase (converts dopamine to NE). Deficiency may be precipitated by tea and toast diet. Scurvy\u2014swollen gums, easy bruising, petechiae, hemarthrosis, anemia, poor wound Vitamin C deficiency causes sCurvy due to a healing, perifollicular and subperiosteal Collagen hydroCylation defect. hemorrhages, \u201ccorkscrew\u201d hair. Weakened immune response. Nausea, vomiting, diarrhea, fatigue, calcium oxalate nephrolithiasis (excess oxalate from vitamin C metabolism). Can \u008f\u00a0iron toxicity in predisposed individuals by increasing dietary iron absorption (ie, can worsen hemochromatosis or transfusion-related iron overload). uploaded by medbooksvn","68 SEC TION II Biochemistry\u2003 \uf07d\u2009BIOCHEMISTRY\u2014Nutrition Vitamin D D3 (cholecalciferol) from exposure of skin (stratum basale) to sun, ingestion of fish, milk, plants. D2 (ergocalciferol) from ingestion of plants, fungi, yeasts. FUNCTION Both converted to 25-OH D3 (storage form) in liver and to the active form 1,25-(OH)2 D3 (calcitriol) REGULATION in kidney. DEFICIENCY A \u008f\u00a0intestinal absorption of Ca2+ and Cholesterol \u2192 PO43\u2013. Diet 7-dehydrocholesterol EXCESS \u008f\u00a0bone mineralization at low levels. Sun\/UV exposure Vitamin E \u008f\u00a0bone resorption at higher levels. D2 D3 FUNCTION \u008f\u00a0PTH, \u0090\u00a0Ca2+, \u0090\u00a0PO43\u2013 (Ergocalciferol) (Cholecalciferol) DEFICIENCY \u008e\u00a0\u008f\u00a01,25-(OH)2D3 production. EXCESS 25-hydroxylase 1,25-(OH)2D3 feedback inhibits its own 25-OH D3 production. Ca2+, PO43\u2013 \u2191\u2191 \u008f\u00a0PTH \u008e\u00a0\u008f\u00a0Ca2+ reabsorption and 1\u03b1-hydroxylase\u2191\u2191 Renal tubular cells \u0090\u00a0PO43\u2013 reabsorption in the kidney. 1,25-(OH)2 D3 Rickets in children (deformity, such Bone Intestines as genu varum \u201cbowlegs\u201d A ), osteomalacia in adults (bone pain and muscle weakness), hypocalcemic tetany. Caused by malabsorption, \u0090\u00a0sun exposure, poor diet, chronic kidney disease (CKD), advanced liver disease. Give oral vitamin D to breastfed infants. Darker skin and prematurity predispose to deficiency. Hypercalcemia, hypercalciuria, loss of re\u2191leCaas2e+ danfdro\u2191mPbOo43n\u2013e \u2191 absorption of Reabsorption: \u2191 Ca2+, \u2191 PO43\u2013 appetite, stupor. Seen in granulomatous Ca2+ and PO43\u2013 Urine: Ca2+, PO43\u2013 diseases (\u008f\u00a0activation of vitamin D by epithelioid macrophages). \u2191 Ca2+ and \u2191 PO43\u2013 Includes tocopherol, tocotrienol. Neurologic presentation may appear similar to vitamin B12 deficiency, but without Antioxidant (protects RBCs and megaloblastic anemia, hypersegmented neuronal membranes from free radical damage). neutrophils, or \u008f\u00a0serum methylmalonic acid levels. Hemolytic anemia, acanthocytosis, muscle weakness, demyelination of posterior columns High-dose supplementation may alter metabolism (\u0090 proprioception and vibration sensation) and of vitamin K \u008e\u00a0enhanced anticoagulant effects spinocerebellar tract (ataxia). Closely mimics of warfarin. Friedreich ataxia. Risk of enterocolitis in enfants (infants) with excess of vitamin E.","Biochemistry\u2003 \uf07d\u2009BIOCHEMISTRY\u2014Nutrition SEC TION II 69 Vitamin K Includes phytomenadione, phylloquinone, phytonadione, menaquinone. FUNCTION Activated by epoxide reductase to the K is for Koagulation. Necessary for the reduced form, which is a cofactor for the maturation of clotting factors II, VII, IX, DEFICIENCY \u03b3-carboxylation of glutamic acid residues on X, and proteins C and S. Warfarin inhibits various proteins required for blood clotting. vitamin K\u2013dependent synthesis of these factors Zinc Synthesized by intestinal microbiota. and proteins. FUNCTION Neonatal hemorrhage with \u008f\u00a0PT and \u008f\u00a0aPTT Not in breast milk; \u201cbreast-fed infants Don\u2019t DEFICIENCY but normal bleeding time (neonates have Know about vitamins D and K\u201d. Neonates are A sterile intestines and are unable to synthesize given vitamin K injection at birth to prevent vitamin K). Can also occur after prolonged use hemorrhagic disease of the newborn. of broad-spectrum antibiotics or hepatocellular disease. Mineral essential for the activity of 100+ enzymes. Important in the formation of zinc fingers (transcription factor motif). Delayed wound healing, suppressed immunity, male hypogonadism, \u0090\u00a0adult hair (axillary, facial, pubic), dysgeusia, anosmia. Associated with acrodermatitis enteropathica A (congenital defect in intestinal zinc absorption manifesting with triad of hair loss, diarrhea, and inflammatory skin rash around body openings (periorificial) and tips of fingers\/toes (acral). May predispose to alcoholic cirrhosis. Protein-energy malnutrition Kwashiorkor Protein malnutrition resulting in skin lesions, AB edema due to \u0090\u00a0plasma oncotic pressure (due to low serum albumin), liver malfunction \u2002\u2002 (fatty change due to \u0090\u00a0apolipoprotein synthesis Linear growth maintained in acute protein- and deposition). Clinical picture is small child with swollen abdomen A . energy malnutrition (vs chronic malnutrition). Kwashiorkor results from protein- deficient MEALS: Malnutrition Edema Anemia Liver (fatty) Skin lesions (eg, hyperkeratosis, dyspigmentation) Marasmus Malnutrition not causing edema. Diet is deficient in calories but no nutrients are entirely absent. Marasmus results in muscle wasting B . uploaded by medbooksvn","70 SEC TION II Biochemistry\u2003 \uf07d\u2009BIOCHEMISTRY\u2014Nutrition Ethanol metabolism NADPH CYP2E1 NADP+ \u008f NADH\/NAD+ ratio inhibits TCA cycle \u008e\u00a0\u008f\u00a0acetyl-CoA used ROS Microsome in ketogenesis (\u008e\u00a0ketoacidosis), lipogenesis (\u008e\u00a0hepatosteatosis). Fomepizole Disul\ufb01ram \u2013 Females are more susceptible than \u2013 males to effects of alcohol due Alcohol dehydrogenase to \uf090\u00a0activity of gastric alcohol Ethanol Acetaldehyde Acetaldehyde dehydrogenase Acetate dehydrogenase, \uf090\u00a0body size, Cytosol \uf090\u00a0percentage of water in body NAD+ NADH NAD+ NADH Mitochondria weight. H2O2 Catalase H2O NAD+ is the limiting reagent. Alcohol dehydrogenase operates via Peroxisome zero-order kinetics. Gluconeogenesis Glycolysis Ethanol metabolism \u008f NADH\/ Glucose NAD+ ratio in liver, causing: \u2002\u0007Lactic acidosis\u2014\u008f pyruvate NADH NAD+ conversion to lactate \u2002\u0007Fasting hypoglycemia\u2014 Glyceraldehyde-3-P DHAP 4A \u2191 Glycerol-3-P \u0090\u00a0gluconeogenesis due to \u008f\u00a0conversion of OAA to malate (fasting PEP NADH NAD+ \u2002\u0007Ketoacidosis\u2014diversion of hypoglycemia) Pyruvate Q \u2191 Lactate acetyl-CoA into ketogenesis rather than TCA cycle (anion gap metabolic acidosis) \u2191 Triglycerides \u2002\u0007Hepatosteatosis\u2014 \u008f\u00a0conversion (hepatic of DHAP to glycerol-3-P \u2191 OAA Acetyl-CoA \u2191 Ketoacids steatosis) 4A ; acetyl-CoA diverges into S fatty acid synthesis 4B , which NADH Lipogenesis combines with glycerol-3-P to R OAA Ketogenesis synthesize triglycerides 4B Fomepizole\u2014competitive inhibitor of alcohol dehydrogenase; \u2191 Fatty acids preferred antidote for overdoses of methanol or ethylene glycol. Isocitrate NAD+ Alcohol dehydrogenase has higher affinity for ethanol NAD+ TCA cycle NADH Pathways stimulated by \u2191 NADH\/NAD+ ratio than for methanol or ethylene \u2191 Malate \u03b1-KG Pathways inhibited by \u2191 NADH\/NAD+ ratio glycol \u008e\u00a0ethanol can be used as Succinyl- competitive inhibitor of alcohol CoA NAD+ dehydrogenase to treat methanol or ethylene glycol poisoning. NADH Disulfiram\u2014blocks acetaldehyde dehydrogenase \u008e\u00a0\u008f\u00a0acetaldehyde \u008e \u008f\u00a0hangover symptoms \u008e\u00a0discouraging drinking.","Biochemistry\u2003 \uf07d\u2009BIOCHEMISTRY\u2014Metabolism SEC TION II 71 ` \u2009B I O C H E M I S T R Y \u2014 M E TA B O L I S M Enzyme terminology An enzyme\u2019s name often describes its function. For example, glucokinase is an enzyme that catalyzes the phosphorylation of glucose using a molecule of ATP. The following are commonly Kinase used enzyme descriptors. Phosphorylase Catalyzes transfer of a phosphate group from a high-energy molecule (usually ATP) to a substrate Phosphatase (eg, phosphofructokinase). Dehydrogenase Hydroxylase Adds inorganic phosphate onto substrate without using ATP (eg, glycogen phosphorylase). Carboxylase Mutase Removes phosphate group from substrate (eg, fructose-1,6-bisphosphatase 1). Synthase\/synthetase Catalyzes oxidation-reduction reactions (eg, pyruvate dehydrogenase). Adds hydroxyl group (\u2212OH) onto substrate (eg, tyrosine hydroxylase). Transfers carboxyl groups (\u2212COOH) with the help of biotin (eg, pyruvate carboxylase). Relocates a functional group within a molecule (eg, vitamin B12\u2013dependent methylmalonyl-CoA mutase). Joins two molecules together using a source of energy (eg, ATP, acetyl-CoA, nucleotide sugar). Rate-determining enzymes of metabolic processes PROCESS ENZYME REGULATORS Glycolysis Phosphofructokinase-1 (PFK-1) AMP \u2295, fructose-2,6-bisphosphate \u2295 ATP \u229d, citrate\u00a0\u229d Gluconeogenesis Fructose-1,6-bisphosphatase 1 TCA cycle Isocitrate dehydrogenase AMP \u229d, fructose-2,6-bisphosphate \u229d Glycogenesis Glycogen synthase ADP \u2295 ATP \u229d, NADH \u229d Glycogenolysis Glycogen phosphorylase Glucose-6-phosphate \u2295, insulin \u2295, cortisol \u2295 HMP shunt Glucose-6-phosphate dehydrogenase (G6PD) Epinephrine \u229d, glucagon\u00a0\u229d De novo pyrimidine Carbamoyl phosphate synthetase II Epinephrine \u2295, glucagon \u2295, AMP \u2295 synthesis Glucose-6-phosphate \u229d, insulin\u00a0\u229d, ATP \u229d Glutamine-phosphoribosylpyrophosphate NADP+ \u2295 De novo purine (PRPP) amidotransferase NADPH \u229d synthesis Carbamoyl phosphate synthetase I ATP \u2295, PRPP \u2295 Urea cycle Acetyl-CoA carboxylase (ACC) UTP \u229d Fatty acid synthesis AMP \u229d, inosine monophosphate (IMP) \u229d, GMP \u229d Fatty acid oxidation Carnitine acyltransferase I Ketogenesis HMG-CoA synthase (HOMG! I\u2019m starving!) N-acetylglutamate \u2295 Cholesterol synthesis HMG-CoA reductase Insulin \u2295, citrate \u2295 Glucagon \u229d, palmitoyl-CoA \u229d Malonyl-CoA \u229d Insulin \u2295, thyroxine \u2295, estrogen \u2295 Glucagon \u229d, cholesterol\u00a0\u229d uploaded by medbooksvn","72 SEC TION II Biochemistry\u2003 \uf07d\u2009BIOCHEMISTRY\u2014Metabolism Metabolism sites Fatty acid oxidation (\u03b2-oxidation), acetyl-CoA production, TCA cycle, oxidative phosphorylation, Mitochondria ketogenesis. Cytoplasm Glycolysis, HMP shunt, and synthesis of cholesterol (SER), proteins (ribosomes, RER), fatty acids, and nucleotides. Both Heme synthesis, urea cycle, gluconeogenesis. Hugs take two (both). Summary of pathways Galactokinase (mild galactosemia) Galactose metabolism Galactose-1-phosphate Galactose B Requires biotin cofactor uridyltransferase (severe galactosemia) Galactose-1-phosphate Glucose Glycolysis T Requires thiamine cofactor (TPP) Hexokinase\/glucokinase Glucose-6-phosphatase Glycogen # Irreversible, important point of regulation (von Gierke disease) Glucose-6-phosphate HMP shunt dehydrogenase Transketolase UDP-glucose Glucose-1-phosphate Glucose-6-phosphate 6-phosphogluconolactone Phosphofructokinase-1 Fructose-1,6-bisphosphatase 1 Glycogenesis \/ glycogenolysis Fructose-6-phosphate T Ribulose-5-phosphate Gluconeogenesis Fructose metabolism Fructose-1,6-bisphosphate Fructokinase (essential fructosuria) Aldolase B (fructose intolerance) Glyceraldehyde-3-P DHAP Fructose-1-phosphate Fructose Aldolase B (liver), A (muscle) 1,3-bisphosphoglycerate Glyceraldehyde Triose phosphate isomerase Pyruvate kinase 3-phosphoglycerate Glycerol Lipid metabolism Pyruvate dehydrogenase Pyruvate carboxylase 2-phosphoglycerate Triglycerides PEP carboxykinase Citrate synthase Phosphoenolpyruvate (PEP) Fatty acids Isocitrate dehydrogenase \u03b1-ketoglutarate dehydrogenase Alanine Pyruvate Lactate Malonyl-CoA Cholesterol Carbamoyl phosphate synthetase I Mevalonate Ornithine transcarbamylase B T B Propionyl-CoA carboxylase HMG-CoA reductase Acetyl-CoA Acetoacetyl-CoA HMG-CoA NH3 + CO2 Aspartate Oxaloacetate Citrate Acetoacetate Citrulline Isocitrate \u03b2-hydroxybutyrate Carbamoyl phosphate Argininosuccinate Malate TCA cycle Fumarate Ketogenesis Ornithine \u03b1-ketoglutarate Odd-chain fatty acids, Urea cycle T isoleucine, valine, methionine, threonine, pyrimidines Arginine Succinate Succinyl-CoA Methylmalonyl-CoA Propionyl-CoA Urea B12 B H2O Protein metabolism","Biochemistry\u2003 \uf07d\u2009BIOCHEMISTRY\u2014Metabolism SEC TION II 73 Activated carriers CARRIER MOLECULE CARRIED IN ACTIVATED FORM Universal electron ATP Phosphoryl groups acceptors NADH, NADPH, FADH2 Electrons CoA, lipoamide Acyl groups Hexokinase vs Biotin CO2 glucokinase Tetrahydrofolates 1-carbon units S-adenosylmethionine (SAM) CH3 groups TPP Aldehydes Nicotinamides (NAD+, NADP+ from vitamin B3) NADPH is a product of the HMP shunt. and flavin nucleotides (FAD from vitamin B2). NADPH is used in: NAD+ is generally used in catabolic processes to \u0083\t Anabolic processes \u0083\t Respiratory burst carry reducing equivalents away as NADH. \u0083\t Cytochrome P-450 system NADPH is used in anabolic processes (eg, \u0083\t G\u0007 lutathione reductase steroid and fatty acid synthesis) as a supply of reducing equivalents. Phosphorylation of glucose to yield glucose-6-phosphate is catalyzed by glucokinase in the liver and hexokinase in other tissues. Hexokinase sequesters glucose in tissues, where it is used even when glucose concentrations are low. At high glucose concentrations, glucokinase helps to store glucose in liver. Glucokinase deficiency is a cause of maturity onset diabetes of the young (MODY) and gestational diabetes. Hexokinase Glucokinase Location Most tissues, except liver Liver, \u03b2 cells of pancreas and pancreatic \u03b2 cells Km Lower (\u008f\u00a0affinity) Higher (\u0090\u00a0affinity) Vmax Lower (\u0090\u00a0capacity) Higher (\u008f\u00a0capacity) Induced by insulin No Yes Feedback inhibition by Glucose-6-phosphate Fructose-6-phosphate uploaded by medbooksvn","74 SEC TION II Biochemistry\u2003 \uf07d\u2009BIOCHEMISTRY\u2014Metabolism Glycolysis regulation, Net glycolysis (cytoplasm): key enzymes Glucose + 2 Pi + 2 ADP + 2 NAD+ \u008e 2 pyruvate + 2 ATP + 2 NADH + 2 H+ + 2 H2O. REQUIRE ATP Equation not balanced chemically, and exact balanced equation depends on ionization state of reactants and products. PRODUCE ATP Glucose Hexokinase\/glucokinase Glucose-6-P Glucose-6-P \u229d hexokinase. Fructose-6-P \u229d glucokinase. Fructose-6-P Phosphofructokinase-1 Fructose-1,6-BP AMP \u2295, fructose-2,6-bisphosphate \u2295. (rate-limiting step) ATP \u229d, citrate \u229d. 1,3-BPG 3-PG Fructose-1,6-bisphosphate \u2295. Pyruvate ATP \u229d, alanine \u229d, glucagon \u229d. Phosphoglycerate kinase Phosphoenolpyruvate Pyruvate kinase Regulation by Fructose bisphosphatase-2 (FBPase-2) and phosphofructokinase-2 (PFK-2) are the same fructose-2,6- bifunctional enzyme whose function is reversed by phosphorylation by protein kinase A. bisphosphate FBPase-1 Gluconeogenesis Fructose-6-P Fructose-1,6-BP Glycolysis PFK-1 FBPase-2 PFK-2 active in active in fasting state fed state Fructose-2,6-BP Fasting state: \u008f\u00a0glucagon \u008e \u008f\u00a0cAMP \u008e\u00a0\u008f\u00a0protein FaBian the Peasant (FBP) has to work hard kinase A \u008e \u008f\u00a0FBPase-2, \u0090\u00a0PFK-2, less when starving. glycolysis, more gluconeogenesis. Fed state: \u008f\u00a0insulin \u008e \u0090\u00a0cAMP \u008e \u0090\u00a0protein Prince FredericK (PFK) works only when fed. kinase A \u008e \u0090\u00a0FBPase-2, \u008f\u00a0PFK-2, more glycolysis, less gluconeogenesis. Pyruvate Mitochondrial enzyme complex linking The complex is similar to the \u03b1-ketoglutarate dehydrogenase dehydrogenase complex (same cofactors, complex glycolysis and TCA cycle. Differentially similar substrate and action), which converts \u03b1-ketoglutarate \u008e succinyl-CoA (TCA cycle). regulated in fed (active)\/fasting (inactive) states. Reaction: pyruvate + NAD+ + CoA \u008e acetyl- The lovely coenzymes for nerds. Arsenic inhibits lipoic acid. Arsenic poisoning CoA + CO2 + NADH. Contains 3 enzymes requiring 5 cofactors: clinical findings: imagine a vampire (pigmentary skin changes, skin cancer), vomiting and having 1.\u2002 Thiamine pyrophosphate (B1) diarrhea, running away from a cutie (QT 2.\u2002 Lipoic acid prolongation) with garlic breath. 3.\u2002 CoA (B5, pantothenic acid) 4.\u2002 FAD (B2, riboflavin) 5.\u2002 NAD+ (B3, niacin) Activated by: \u008f\u00a0NAD+\/NADH ratio, \u008f\u00a0ADP \u008f\u00a0Ca2+.","Biochemistry\u2003 \uf07d\u2009BIOCHEMISTRY\u2014Metabolism SEC TION II 75 Pyruvate Causes a buildup of pyruvate that gets shunted to lactate (via LDH) and alanine (via ALT). dehydrogenase X-linked. complex deficien y Neurologic defects, lactic acidosis, \u008f\u00a0serum alanine starting in infancy. FINDINGS \u008f\u00a0intake of ketogenic nutrients (eg, high fat content or \u008f\u00a0lysine and leucine). TREATMENT Pyruvate metabolism Functions of different pyruvate metabolic Glucose pathways (and their associated cofactors): ALT Pyruvate LDH \u0007Alanine aminotransferase (B6): alanine NAD+ carries amino groups to the liver from Alanine Cytosol NADH NAD+ Lactate Cahill cycle Mitochondria + H+ Cori cycle muscle CO2 + ATP PC PDH \u0007Pyruvate carboxylase (B7): oxaloacetate ogenase can replenish TCA cycle or be used in Oxaloacetate NADH CO2 + H+ Acetyl-CoA gluconeogenesis P\u0007 yruvate dehydrogenase (B1, B2, B3, B5, lipoic acid): transition from glycolysis to the TCA cycle \u0007Lactic acid dehydrogenase (B3): end of anaerobic glycolysis (major pathway in RBCs, WBCs, kidney medulla, lens, testes, and cornea) TCA cycle Pyruvate (3C) Also called Krebs cycle. Pyruvate \u008e acetyl-CoA CO2 + NADH PD*H ATP produces 1 NADH, 1 CO2. Acetyl-CoA The TCA cycle produces 3 NADH, 1 FADH2, NADH 2 CO2, 1 GTP per acetyl-CoA = 10 ATP\/ Acetyl-CoA (2C) ATP acetyl-CoA (2\u00d7 everything per glucose). TCA NADH Oxalo- Citrate synthase Citrate (6C) cycle reactions occur in the mitochondria. acetate * cis-Aconitate (4C) Isocitrate (6C) \u03b1-ketoglutarate dehydrogenase complex Malate (4C) requires the same cofactors as the pyruvate Fumarate (4C) * CO2 + NADH dehydrogenase complex (vitamins B1, B2, B3, Isocitrate ATP B5, lipoic acid). dehydrogenase Citrate is Krebs\u2019 starting substrate for making NADH ADP oxaloacetate. FADH2 \u03b1-KG (5C) Succinate (4C) \u03b1-KG d*ehydr CO2 + NADH GTP + CoA Succinyl- Succinyl-CoA CoA (4C) NADH ATP * Enzymes are irreversible uploaded by medbooksvn","76 SEC TION II Biochemistry\u2003 \uf07d\u2009BIOCHEMISTRY\u2014Metabolism Electron transport NADH electrons are transferred to complex I. 1 NADH \u008e\u00a02.5 ATP; 1 FADH2 \u008e\u00a01.5 ATP chain and oxidative FADH2 electrons are transferred to complex II NADH electrons from glycolysis enter phosphorylation (at a lower energy level than NADH). mitochondria via the malate-aspartate or The passage of electrons results in the formation glycerol-3-phosphate shuttle. Aerobic metabolism of one glucose molecule of a proton gradient that, coupled to oxidative produces 32 net ATP via malate-aspartate phosphorylation, drives ATP production. ATP shuttle (heart and liver), 30 net ATP via hydrolysis can be coupled to energetically glycerol-3-phosphate shuttle (muscle). unfavorable reactions. Anaerobic glycolysis produces only 2 net ATP Uncoupling proteins (found in brown fat, which per glucose molecule. has more mitochondria than white fat) produce Aspirin overdose can also cause uncoupling heat by \u008f\u00a0inner mitochondrial membrane of oxidative phosphorylation resulting in permeability \u008e\u00a0\u0090\u00a0proton gradient. ATP synthesis hyperthermia. stops, but electron transport continues. NADH NAD+ FADH2 FAD ADP + Pi ATP 1\/2 O2 + 2H+ H2O Mitochondrial matrix CoQ Inner mitochondrial membrane Cyto- chrome c Intermembrane space Complex I Complex II Complex III Complex IV Complex V (succinate dehydrogenase) Uncoupling proteins H+ H+ Cyanide, H+ H+ Aspirin overdose CO Gluconeogenesis, All enzymes may be subject to activation by Pathway produces fresh glucose. irreversible enzymes glucagon in fasting state. Requires biotin, ATP. Activated by acetyl-CoA. Pyruvate carboxylase In mitochondria. Pyruvate \u008e oxaloacetate. Requires GTP. Phosphoenolpyruvate In cytosol. Oxaloacetate Citrate \u2295, AMP \u229d, fructose 2,6-bisphosphate \u229d. carboxykinase \u008e\u00a0phosphoenolpyruvate (PEP). Fructose-1,6- In cytosol. Fructose-1,6-bisphosphate bisphosphatase 1 \u008e\u00a0fructose-6-phosphate. Glucose-6- In ER. Glucose-6-phosphate \u008e glucose. phosphatase Occurs primarily in liver; serves to maintain euglycemia during fasting. Enzymes also found in kidney, intestinal epithelium. Deficiency of the key gluconeogenic enzymes causes hypoglycemia. (Muscle cannot participate in gluconeogenesis because it lacks glucose-6-phosphatase). Odd-chain fatty acids yield 1 propionyl-CoA during metabolism, which can enter the TCA cycle (as\u00a0succinyl-CoA), undergo gluconeogenesis, and serve as a glucose source (It\u2019s odd for fatty acids to make glucose). Even-chain fatty acids cannot produce new glucose, since they yield only acetyl- CoA equivalents.","Biochemistry\u2003 \uf07d\u2009BIOCHEMISTRY\u2014Metabolism SEC TION II 77 Pentose phosphate Also called HMP shunt. Provides a source of NADPH from abundantly available glucose-6-P pathway (NADPH is required for reductive reactions, eg, glutathione reduction inside RBCs, fatty acid and cholesterol biosynthesis). Additionally, this pathway yields ribose for nucleotide synthesis. Two REACTIONS distinct phases (oxidative and nonoxidative), both of which occur in the cytoplasm. No ATP is used or produced. Oxidative (irreversible) Sites: lactating mammary glands, liver, adrenal cortex (sites of fatty acid or steroid synthesis), RBCs. Nonoxidative \t\t (reversible) NADP+ NADPH NADP+ NADPH CO2 Ribulose-5-Pi Glucose-6-PiGlucose-6-P dehydrogenase 6-Phosphogluconate Fructose-6-Pi Transketolase, B\u2081 Phosphopentose isomerase Ribose-5-Pi Fructose Nucleotide 1,6-bisphosphate synthesis DHAP Glyceraldehyde-3-Pi Glucose-6-phosphate NADPH is necessary to keep glutathione X-linked recessive disorder; most common dehydrogenase reduced, which in turn detoxifies free radicals human enzyme deficiency; more prevalent deficien y and peroxides. \u0090\u00a0NADPH in RBCs leads to among descendants of populations in malaria- hemolytic anemia due to poor RBC defense endemic regions (eg, sub-Saharan Africa, against oxidizing agents (eg, fava beans, Southeast Asia). sulfonamides, nitrofurantoin, primaquine). Infection (most common cause) can also Heinz bodies\u2014denatured globin chains precipitate hemolysis; inflammatory response precipitate within RBCs due to oxidative stress. produces free radicals that diffuse into RBCs, causing oxidative damage. Bite cells\u2014result from the phagocytic removal of Heinz bodies by splenic macrophages. Think, \u201cBite into some Heinz ketchup.\u201d Glucose-6-P NADP+ 2 GSH H2O2 (reduced) Glucose-6-P Glutathione Glutathione dehydrogenase reductase peroxidase 6-phosphogluconolactone NADPH GSSG 2H2O (oxidized) uploaded by medbooksvn","78 SEC TION II Biochemistry\u2003 \uf07d\u2009BIOCHEMISTRY\u2014Metabolism Disorders of fructose metabolism Essential fructosuria Hereditary fructose intolerance ENZYME DEFICIENCY Fructokinase (autosomal recessive) Aldolase B (autosomal recessive) PATHOPHYSIOLOGY Fructose is not trapped into cells. Hexokinase Fructose-1-phosphate accumulates \u008e \u0090\u00a0available becomes 1\u00b0 pathway for converting fructose to phosphate \u008e\u00a0inhibition of glycogenolysis and fructose-6-phosphate. gluconeogenesis. PRESENTATION (SIGNS\/SYMPTOMS) Asymptomatic, benign. Fructose appears in Hypoglycemia, jaundice, cirrhosis, vomiting. blood and urine (fructokinase deficiency is Symptoms only present following consumption kinder). of fruit, juice, or honey. ADDITIONAL REMARKS Urine dipstick will be \u229d (tests for glucose only); reducing sugar can be detected in the urine (nonspecific test for inborn errors of carbohydrate metabolism). TREATMENT \u2013 \u0090\u00a0intake of fructose, sucrose (glucose + fructose), and sorbitol (metabolized to fructose). Triose phosphate Dihydroxyacetone-P isomerase Fructose Fructokinase Fructose-1-P Aldolase B Glyceraldehyde Triose kinase Glyceraldehyde-3-P Glycolysis ATP ADP ATP ADP NADH NAD+ Glycerol Disorders of galactose metabolism Classic galactosemia Galactokinase deficiency ENZYME DEFICIENCY Galactokinase (autosomal recessive). Galactose-1-phosphate uridyltransferase (autosomal recessive). PATHOPHYSIOLOGY Galactitol accumulates if diet has galactose. Damage caused by accumulation of toxic PRESENTATION (SIGNS\/SYMPTOMS) substances (eg, galacitol). Relatively mild\/benign condition (galactokinase TREATMENT deficiency is kinder). Symptoms start when infant is fed formula or breast milk \u008e\u00a0failure to thrive, jaundice, Galactose appears in blood (galactosemia) and hepatomegaly, infantile cataracts (galacitol urine (galactosuria); infantile cataracts. May deposition in eye lens), intellectual disability. present as failure to track objects or develop Can predispose neonates to E coli sepsis. social smile. Exclude galactose and lactose (galactose + \u2013 glucose) from diet. Galactokinase Galactose-1-P Uridylyltransferase Glucose-1-P Galactose ATP ADP UDP-Glu UDP-Gal 4-Epimerase Glycolysis\/glycogenesis Aldose reductase Galactitol","Biochemistry\u2003 \uf07d\u2009BIOCHEMISTRY\u2014Metabolism SEC TION II 79 Sorbitol An alternative method of trapping glucose in the cell is to convert it to its alcohol counterpart, sorbitol, via aldose reductase. Some tissues then convert sorbitol to fructose using sorbitol Lactase deficien y dehydrogenase; tissues with an insufficient amount\/activity of this enzyme are at risk of intracellular sorbitol accumulation, causing osmotic damage (eg, cataracts, retinopathy, and FINDINGS peripheral neuropathy seen with chronic hyperglycemia in diabetes). TREATMENT High blood levels of galactose also result in conversion to the osmotically active galactitol via aldose Amino acids reductase. Essential Acidic Liver, ovaries, and seminal vesicles have both enzymes (they lose sorbitol). Basic Glucose Aldose reductase Sorbitol Sorbitol dehydrogenase Fructose NADPH NAD+ Lens has primarily Aldose reductase. Retina, Kidneys, and Schwann cells have only aldose reductase (LARKS). Insufficient lactase enzyme \u008e dietary lactose intolerance. Lactase functions on the intestinal brush border to digest lactose (in milk and milk products) into glucose and galactose. Primary: age-dependent decline after childhood (absence of lactase-persistent allele), common in people of Asian, African, or Native American descent. Secondary: loss of intestinal brush border due to gastroenteritis (eg, rotavirus), autoimmune disease. Congenital lactase deficiency: rare, due to defective gene. Stool demonstrates \u0090\u00a0pH and breath shows \u008f\u00a0hydrogen content with lactose hydrogen breath test (H+ is produced when colonic bacteria ferment undigested lactose). Intestinal biopsy reveals normal mucosa in patients with hereditary lactose intolerance. Bloating, cramps, flatulence (all due to fermentation of lactose by colonic bacteria \u008e gas), and osmotic diarrhea (undigested lactose). Avoid dairy products or add lactase pills to diet; lactose-free milk. Only l-amino acids are found in proteins. PVT TIM HaLL: Phenylalanine, Valine, Tryptophan, Threonine, Isoleucine, Methionine, Histidine, Leucine, Lysine. Glucogenic: Methionine, histidine, valine. We met his valentine, who is so sweet (glucogenic). Glucogenic\/ketogenic: Isoleucine, phenylalanine, threonine, tryptophan. Ketogenic: leucine, lysine. The only purely ketogenic amino acids. Aspartic acid, glutamic acid. Negatively charged at body pH. Arginine, histidine, lysine. Arginine is most basic. Histidine has no charge at body pH. Arginine and histidine are required during periods of growth. Arginine and lysine are \u008f\u00a0in histones which bind negatively charged DNA. His lys (lies) are basic. uploaded by medbooksvn"]
Search
Read the Text Version
- 1
- 2
- 3
- 4
- 5
- 6
- 7
- 8
- 9
- 10
- 11
- 12
- 13
- 14
- 15
- 16
- 17
- 18
- 19
- 20
- 21
- 22
- 23
- 24
- 25
- 26
- 27
- 28
- 29
- 30
- 31
- 32
- 33
- 34
- 35
- 36
- 37
- 38
- 39
- 40
- 41
- 42
- 43
- 44
- 45
- 46
- 47
- 48
- 49
- 50
- 51
- 52
- 53
- 54
- 55
- 56
- 57
- 58
- 59
- 60
- 61
- 62
- 63
- 64
- 65
- 66
- 67
- 68
- 69
- 70
- 71
- 72
- 73
- 74
- 75
- 76
- 77
- 78
- 79
- 80
- 81
- 82
- 83
- 84
- 85
- 86
- 87
- 88
- 89
- 90
- 91
- 92
- 93
- 94
- 95
- 96
- 97
- 98
- 99
- 100
- 101
- 102
- 103
- 104
- 105
- 106
- 107
- 108
- 109
- 110
- 111
- 112
- 113
- 114
- 115
- 116
- 117
- 118
- 119
- 120
- 121
- 122
- 123
- 124
- 125
- 126
- 127
- 128
- 129
- 130
- 131
- 132
- 133
- 134
- 135
- 136
- 137
- 138
- 139
- 140
- 141
- 142
- 143
- 144
- 145
- 146
- 147
- 148
- 149
- 150
- 151
- 152
- 153
- 154
- 155
- 156
- 157
- 158
- 159
- 160
- 161
- 162
- 163
- 164
- 165
- 166
- 167
- 168
- 169
- 170
- 171
- 172
- 173
- 174
- 175
- 176
- 177
- 178
- 179
- 180
- 181
- 182
- 183
- 184
- 185
- 186
- 187
- 188
- 189
- 190
- 191
- 192
- 193
- 194
- 195
- 196
- 197
- 198
- 199
- 200
- 201
- 202
- 203
- 204
- 205
- 206
- 207
- 208
- 209
- 210
- 211
- 212
- 213
- 214
- 215
- 216
- 217
- 218
- 219
- 220
- 221
- 222
- 223
- 224
- 225
- 226
- 227
- 228
- 229
- 230
- 231
- 232
- 233
- 234
- 235
- 236
- 237
- 238
- 239
- 240
- 241
- 242
- 243
- 244
- 245
- 246
- 247
- 248
- 249
- 250
- 251
- 252
- 253
- 254
- 255
- 256
- 257
- 258
- 259
- 260
- 261
- 262
- 263
- 264
- 265
- 266
- 267
- 268
- 269
- 270
- 271
- 272
- 273
- 274
- 275
- 276
- 277
- 278
- 279
- 280
- 281
- 282
- 283
- 284
- 285
- 286
- 287
- 288
- 289
- 290
- 291
- 292
- 293
- 294
- 295
- 296
- 297
- 298
- 299
- 300
- 301
- 302
- 303
- 304
- 305
- 306
- 307
- 308
- 309
- 310
- 311
- 312
- 313
- 314
- 315
- 316
- 317
- 318
- 319
- 320
- 321
- 322
- 323
- 324
- 325
- 326
- 327
- 328
- 329
- 330
- 331
- 332
- 333
- 334
- 335
- 336
- 337
- 338
- 339
- 340
- 341
- 342
- 343
- 344
- 345
- 346
- 347
- 348
- 349
- 350
- 351
- 352
- 353
- 354
- 355
- 356
- 357
- 358
- 359
- 360
- 361
- 362
- 363
- 364
- 365
- 366
- 367
- 368
- 369
- 370
- 371
- 372
- 373
- 374
- 375
- 376
- 377
- 378
- 379
- 380
- 381
- 382
- 383
- 384
- 385
- 386
- 387
- 388
- 389
- 390
- 391
- 392
- 393
- 394
- 395
- 396
- 397
- 398
- 399
- 400
- 401
- 402
- 403
- 404
- 405
- 406
- 407
- 408
- 409
- 410
- 411
- 412
- 413
- 414
- 415
- 416
- 417
- 418
- 419
- 420
- 421
- 422
- 423
- 424
- 425
- 426
- 427
- 428
- 429
- 430
- 431
- 432
- 433
- 434
- 435
- 436
- 437
- 438
- 439
- 440
- 441
- 442
- 443
- 444
- 445
- 446
- 447
- 448
- 449
- 450
