Class_12_Chemistry_Study material_Ch14

Subject: Chemistry Study Material Class: XII th Bio molecules Living system are made up of various complex molecules like carbohydrates, proteins, nucleic acids and lipids which are termed as bio molecules. Carbohydrates: These are hydrates of carbon having formula CX(H2O)Y . There are many compound which fit into this formula but are not carbohydrates eg. CH COOH and many compound which are not carbohyds but do not fit into this 3 formula. E.g. rhamnose C6H12O5 Hence carbohydrates may be defied as optically active polyhydroxy aldehydes or ketones or compounds which produce such units on hydrolyles. Many carbohydrates are sweet in taste hence called Sugars. E.g. Sucrose is used in home as sugar and Lactose is present in milk. Classification of carbohydrate: (i) Monosaccharides: A carbohydrate that cannot be hydrolysed further to give simple unit of polyhydroxy aldehyde or ketone is called a monosaccharide. Some common examples are glucose, fructose, ribose, etc. (ii) Oligosaccharides: Carbohydrates that yield two to ten monosaccharide units, on hydrolysis, are called oligosaccharides. They are further classified as disaccharides, trisaccharides, tetrasaccharides, etc., depending upon the number of monosaccharides, they provide on hydrolysis. Sucrose on hydrolysis gives one molecule each of glucose and fructose whereas maltose gives two molecules of glucose only. (iii) Polysaccharides: Carbohydrates which yield a large number of monosaccharide units on hydrolysis are called polysaccharides. Some common examples are starch, cellulose, glycogen, gums, etc. polysaccharides are not sweet in taste, hence they are also called non-sugars. Reducing sugar: Carbohydrates which reduce Tollen’ s reagent and Fehling’ s solution are called reducing sugar. Disacchrides like maltose and lactose are also reducing sugars. Non reducing sugars: Those carbohydrates which do not reduce Tollen’ s reagent and Fehling solution are non reducing sugars. All polydacchride and disacchrides bonded by their reducing centers are non reducing sugar. e.g., cellulose, starch sucrose. Methods of preparations and properties of monosaccharides: All carbohydrates are either monosaccharides or get converted into monosaccharides on hydrolysis. Glucose is aldohexose whereas fructose is ketohexose. Glucose occurs in nature in free as well as in combined from. It is present in sweet fruits and honey. Ripe grapes contain 20% of glucose, therefore, it is called dextrose or grape sugar. Preparation of Glucose: (i) From Surcose: It sucrose is boiled with dilute HCl or H2SO4 in alcoholic solution, glucose and fructose are obtained in equal amounts. C12H22O11 + H2O H+ C6H12O6 + C6H12O6 Sucrose Glucose Fructose (ii) From Starch: Commercially, glucose is obtained by hydrolysis of starch by boiling it with dil. H2SO4 at 393 K under pressure. (C6H12O5 )n + nH2O ⎯⎯⎯H+⎯⎯→ nC6 H12 O6 393 K, 2-3 bar Starch or cellulose Glucose Structure of Glucose: It was assigned following structure on the basis of its chemical properties. Glucose is Currently named as D (+)-Glucose ‘ D’ stands for configuration whereas (+) represents dextrorotatory nature of molecule. ‘ D’ and ‘ L’ has no relationship with the optical activity of the compound. Glyceraldehydes (reference compund) contain one asymmetric carbon atom and exists in two enantiomeric forms as shown below: CHO CHO H OH HO H CH2OH CH2OH D(+)-Glyceraldehyde L(-)-Glyceraldehyde All those compound which can be chemically correlated to D(+) isomer of glyceraldehydes are said to have D- configuration in which – OH group on first chiral ‘ C’ atom from the bottom is on right hand side whereas those 1

compounds which are correlated to L(-) isomer of glyceraldehydes have L-configuration, which have – OH group on left hand side e.g., CHO CHO H OH HO H H OH H OH H OH CH2OH CH2OH D(+)-Glyceraldehyde D(+)-Glucose Cyclic structures of glucose (hemiacetal forms): The open structure chain of glucose explained most of its properties but the following reactions and facts could not be explained by this structure. 1.Despite having the aldehyde group, glucose does not give 2,4- DNP test, Schiff`s test and it does not form the hydrogensulphite addition product with NaHSO3 . 2. The pentaacetate of glucose does not react with hydroxylamine indicating the absence of free _CHO group. 3. Glucose is found to exist in two different crystalline forms which are named as  and β . The  -form of glucose is obtained by crystallization from concentrated solution of glucose at 303 Kwhile the β -form is obtained by crystallization from hot and saturated aqueous solution at 371 K.These are called hemiacetal forms. Anomers: The two cyclic forms of glucose (  and  ) having difference in configuration of OH group at G, are called anomers. CHO CHO Mutarotation:  -glucose has specific rotation of +1120 and  form H OH H OH has +19.20 . If either of there two forms is dissolved in water and HO H HO H allowed to stand, the specific rotation of solution changes and H OH HO H reaches a S constant value at +52.50 . This change in specific H OH H OH rotation is called mutarotation. CH2 O H (glucose) CH2 O H (galactose) Epimers: Monosaccharides having difference in configuration at any other carbon (except C1 ) are called epimers e.g. glucose and mannose are C2 epimers & glucose and galactose are C4 epimers. Haworth projection or pyranose forms of glucose: (i) The group towards right are written below the plane and the groups towards left are written above the plane. (ii) Between CH2OH and H, CH2OH is written above the plane. Properties of Glucose: Glucose has one aldehydic group, one primary alcoholic group (- CH2OH ) and four secondary alcoholic groups (- CHOH ) and gives the following reactions. (i) Acetylation of glucose with acetic anhydride gives glucose pentaacetate confirming the presence of five hydroxy1 group 2

CHO CHO ll ( CI HOH)4 + 5(CH3CO)2O → (CC| HHO2OC_OCCOH_3C)4H+3 5CH3COOH CH2OH . Acetic anhydride Glucose Glucose pentaacetate (ii) Glucose reacts with hydroxylamine to give monoxime. CHO CH =NOH l l ( CI HOH)4 + H2NOH → ( CI HOH)4 CH2OH CH2OH Hydroxyl Glucose monoxime amine (iii) Glucose reacts with hydrogen cyanide to give glucose cyanohydrin. O OH ll l C _ H H_ C _CN l l + → (CHOH) HCN l 4 (CH OH) l CH 2 OH CH 2OH Glucose cyanahydrin These reaction confirm the presence of carbonyl group. (iv) Glucose reduces ammonical silver nitrate (Tollens’ regent) to metallic silver CHO COOH l l + Ag(NH3 )2+ → (C + 2Ag (CH OH) HOH ) l 4 l 4 CH OH (tollen`s reagent) CH2OH 2 (Gluconic acid) (v) Glucose reduces Fehling’ s solution and gives brick red precipitate due to formation of curprous Oxide ( Cu2O ). CHO COOH l l l (CHOH) + 2CuSO4 + 4NaOH → (Cl HOH)4 + Cu2O + 2Na2SO4 + 2H2O l 4 CH2OH (brick red ppt.) CH2OH (vi) On oxidation with bromine water, glucose forms gluconic acid. CHO ⎯B⎯(rH2 ⎯O/ HB2r⎯)O→ COOH l l (CHOH) (Cl HOH)4 + HBr l C H2OH CH2OH (Glucose) (Gluconic acid) 3

(vii) On oxidation with strong oxidising agent like concentrated HNO3 glucose gives gluconic acid and saccharic acid showing the presence of primary alcoholic group. Gluconic acid gets oxidized to saccharic acid. CHO COOH C OOH Conc. l Conc. l l (CH (Cl HOH)4 (CH OH) ⎯⎯HNO⎯3 → OH ) ⎯HNO⎯3 ⎯ l 4 l 4 CH2OH COOH CH2OH (Glucose) (Saccharic acid) (Gluconic acid) (viii) Glucose on reduction with H2 in presence of nickel as catalyst or sodium amalgam in aqueous solution or NaBH4 gives sorbitol. CHO l CH2OH l ⎯o⎯r N⎯NaiB⎯H4 → (Cl HOH)4 (Cl HOH)4 + H2 CH2OH CH2OH (Glucose) (Sarbitol) (ix) Glucose on prolonged heating with HI forms n-hexane, suggesting all the six carbon atoms in glucose are linked linearly. HOCH2 _(CHOH)4_ CHO ⎯⎯reHdIP⎯→CH3 _ CH2 _ CH2 _ CH2 _ CH2 _ CH3 + 6H2O Glucose n-Hexane (x) D-Glucose reacts with pheny1hydrazine to give glucose pheny1hyrazone which is soluble in water. If excess of pheny1hydrazine is used, dihydrazone, known as Glucosazone is formed. CHO H_CCl _HO=HN-N⎯HC⎯C66HH⎯5N5H⎯NH⎯2→ Cl H=N-NHC6H5 Cl H=N-NHC6 H5 H_lC_OH ⎯C⎯6H5⎯NHN⎯H2 → l C=O ⎯⎯C6H⎯5NH⎯NH⎯2→ C= N-NHC6 H5 (lCHOH)3 l l l -H2O CH2OH (Cl HOH)3 (CHOH)3 (Cl HOH)3 CH2OH CH2OH CH2OH (D-glucose) D-Glucose phenylhydrazone D-glucosazone Fructose: Fructose also has the molecular formula C6H12O6 and on the basis of its reaction it was found to contain a ketonic functional group at carbon number 2 and six carbons in straight chain as in the case of glucose. It belongs to D- series and is a laevorotatory compound. It is appropriately written as D-(-)- fructose. It also exists in two cyclic forms which are obtained by the addition of OH at C5 to the ( C=O) group. The ring, thus formed is a five membered ring and is named as furanose with analogy to the compound furan. Furan is a five membered cyclic compound with one oxygen and four carbon atoms .The cyclic structure of two anomers of fructose are represented by Haworth structure as given. Disaccharides: The two monosaccharides are joined together to form disaccharide by an oxide linkage. 4

Glycosidic linkage: The bond formed between two mono sacchrides by removal of water molecule is called glycosidic linkage or glycosidic bond. (i) Maltose: Another disaccharide, maltose is composed of two  -D-glucose unit in which C1 of one glucose (I) is linked to C4 of another glucose unit (II). The free aldehyde group can be produced at C1 of second glucose in solution and it shows reducing properties hence it is a reducing sugar. (ii) Sucrose: One of the common disaccharides is sucrose which on hydrolysis gives equimolar mixture of D-(+)-glucose and D-(-) fructose. C12H22O11 + H2O → C6H12O6 + C6H12O6 Sucrose D-(+)-Glucose D-(-)-Frutose These two monosaccharides are held together by a glycosidic linkage between C1 of  -glucose and C2 of  -fructose. Since the reducing groups of glucose and fructose are involved in glycosidic bond formation, sucrose is a non reducing sugar. Sucrose is dextrorotatory but after hydrolysis it gives dextrorotatory glucose and laevorotatory fructose. Since the laevorotation of fructose (-92.4 0 ) is more than dextrorotation of glucose (+ 52.5 0 ), the mixture is laevorotatory. Thus, hydrolysis of sucrose brings about a change in the sign of rotation, from dextro (+) to laevo (-) and the product is named as invert sugar. (iii) Lactose: It is more commonly known as milk sugar since this disaccharide is found in milk. It is composed of  -D-galactose and  -D-glucose by 1,4 link. Since reducing centre of one unit ( C1 carbon) is free. Hence it is also a reducing sugar. Polysaccharides: Polysaccharides contain a large number of monosaccharide units joined together by glycosidic linkages. They mainly act as the food storage of structural materials. (i) Starch: Starch is the main storage polysaccharide of plants. It is the most important dietary source for human being. High content is a starch is found in cereals, roots, tubers and some vegetables. It is a polymer of  - glucose and consists of two components – Amylose and Amylopectin. Difference between Amylose and Amylopectin S.no. Amylose Amylopectin 1. It is water soluble. It is insoluble in water. 2. It is 15-20% of starch. It is 80-85% of starch. 3. It is long straight chain. It is long branched chain. 4. It has 200 – 1000  -(D)-glucose units held by C1-C4 It has 25-30 D-glucose units joined by C1-C4 5. glycosidic linkage. glycosidic linkage. It gives blue colour with iodine. It does not give blue colour with iodine. (ii) Cellulose: Cellulose occurs exclusively in plants and it is the most abundant organic substance in plant kingdom. It is a predominant constituent of cell wall of plant cells. Cellulose is a straight chain polysaccharide composed only of  -D-glucose units which are joined by glycosidic linkage between C1 of one glucose unit and C4 of the next glucose unit. (iii) Glycogen: The carbohydrates are stored in animal body as glycogen. It is also known as animal starch because its structure is similar to amylopectin and is rather more highly branched. It is present in liver, muscles and brain. When the body needs glucose, enzymes break the glycogen down to glucose. Glycogen is also found in yeast and fungi. Importance of Carbohydrates: (i) They are essential for plants and animals as a source of energy. (ii) Honey consists of mixture of carbohydrates which is source of energy. (iii) They store energy in the form of starch and cellulose in plants and glycogen in animals and human beings. (iv) Cellulose is used for mixing cotton fibre rayon, plastic (cellulose acetate used for photographic film), guncotton (cellulose nitrate), an explosive. (v) They are used in textile, paper and alcohol industry. (vi) D-Ribose and D-oxyribose are present in DNA and RNA respectively. (vii) They are also found in combination with proteins and lipids. 5

Amino acids: Amino acids contain amino ( NH2 ) group and carboxyl (-COOH) group. Depending upon the relative position of NH2 group w.r.t COOH group these are named as  ,  , γ amino acid. Glycine is the simplest amino acid. R-CH-COOH l Proteins give only  -amino acids on hydrolyes. NH2 (α-amino acids) • Except glycine all other amino acids are optically active. • These are colourless, crystallive solids, water soluble and have high melting + point. Nl H3 R-CH-COO - Zwitter ion or dipolar ion: Amino acids exist in ionic form which is formed by transfer of proton from COOH to NH2 group. It is called zwitter ion. (Zwitter ion) In zwitter ion form amino acid show amphoteric behaviour. Isoelectric point: The pH at which dipolar ion (zwitter ion) does not migrate to either electrode in the presence of electric field is called isoelectric point. The amino acids have least solubility at isoelectric point which helps in separation of amino acids. Classification of amino acids: Acidic: Those amino acids which contain two carboxy1 group and one amino group are called acidic amino acids, e.g., Aspartic acid. Basic amino acids: Those amino acids which contain two amino groups and one carboxy1 group are called basic amino acids, e.g., lysine, histidine. Neutral amino acids:Those amino acids which contain one amino and one carboxy1 group are called neutral amino acids e.g., glycine, alanine, etc. Essential amino acids: Those amino acids which are not synthesized by our body are called essential amino acids. They must be part of our diet. Their deficiency leads to diseases such as Kwashiorkor (water balance in the body is disturbed). e.g., pheny1 alanine, tryptophan, histidine etc. Non-essential amino acids: These are synthesized by our body and need not to be taken from external resources. These are also called dispersable amino acidse.g., glycine , alanine etc. Peptide linkage of peptides bond: It is bond formed between COOH group of one amino acid with NH2 group of other amino acid to form amide group. H2 N-CH2 -COOH + H2 N-CH-COOH ⎯⎯⎯→ H2 N-CHPe2p-tiCdeOL-iNnkHage-lCH-COOH l -H2O CH3 CH3 Depending upon the no. of amino acids peptide may be dipeptide, tripeptide or poly peptide. Proteins: These are long chain polymers of  -amino acids. These are present in every part of body and form the fundamental basis of structure and functioning of life. They are required for growth and maintenance of body. Classification of proteins: 1. Fibrous protein: The proteins, which have long and thread-like structure, are called fibrous proteins. The molecules are held together by hydrogen bonds. They are insoluble in water due to strong intermolecular force of attraction. They are chief structural material of animal tissues. ,e.g. keratin, myosin and fibroin are examples of fibrous proteins. 2. Globular protein: There are formed when poly peptide chains are folded to form spherical molecules. These are water soluble and are pH sensitive. e.g., Insulin and albumin. Denaturation of proteins: It is the process of change in the structure of protein by changing temperature, pH or by adding some compounds. Due to this proteins get unfolded and unoiled and loses its biological activity. The soluble proteins become insoluble. For example boiling of egg, curdling of milk etc. Structure of proteins: i) Primary structure of protein: The sequence in which the amino acids are arranged in a protein is called the primary structure of protein. ii) Secondary structure of protein: The polypeptide chain gets folded due to intermolecular hydrogen bonding between the carboxy1 and amino group. In an  -helix, the peptide chain coils and the turns of the coil are held together by hydrogen bonds. Another type of secondary structure is possible in which the protein chain are stretched out. This is the  -pleated sheet structure. 6

iii) Tertiary structure of protein: It is the three-dimensional structure of globular proteins. It arises due to folding and superposition of various secondary structural elements. At normal pH and temperature, each protein will iv) take a shape that is energetically most stable. This shape is specific to a given amino acid sequence and v) is called the native state of a protein. Quaternary structure of protein: Some of the vi) proteins are composed of two or more polypeptide • chain referred to as subunit. The spatial arrangement • of these subunit with respect to each other is known as • quaternary structure. • Enzymes: They are essential biological catalysts • which arte needed to catalyse biochemical reactions, e.g., maltase, lactase, amylase, invertase, vii) etc. Almost all enzymes are globular proteins. They are highly specific and are sensitive to change in pH and temperature. The enzymes which catalyse the oxidation of one substrate with simultaneous reduction of another substrate are named as oxidoreductase enzymes. Active site: The region on the surface of the enzyme to which the reactant molecules (substrates) bind is called active site. The active site of a given enzyme is so shaped that only its specific substrates can fit into it. Therefore enzymes are very specific in their action. Enzymes are needed in very small amount. They reduce magnitude of activation energy. Enzymes are highly specific i.e., they catalyse a particular reaction only. They work at specific pH e.g., salivary amylase becomes inactive in stomach due to acidic pH. They work well at moderate temperature. Vitamins: Vitamins are group of organic compounds which are required in very small amounts for the healthy growth and functioning of animal organism. They cannot be made by organism except vitamin D and so have to be part of our diet. The deficiency of a vitamin can cause a specific disease. Fat soluble vitamins: vitamins A, D, E, K are fat soluble but insoluble in water. They are stored in liver and adipose Vitamin Chemical Name Deficiency Disease Sources of vitamin A Retinol (bright eye Xerophthalmia (hardening of cornea of eye) Cod liver oil, shark liver oil, vitamin) Night blindness carrot. Rice polishing, liver, kidney, butter, milk B1 Thiamine Beri-beri (loss of appetite, fatigue, retarded Milk, rice, yeast, nuts, eggs, growth) green vegetables. B2 Riboflavin Ariboflavinosis (sore throat, burning eyes, Turnip, milk, eggs, yeast, glossitis, dermatitis, cheilosis). vegetables liver, kidney B6 Pyridoxine Nervous disturbance and convulsions. Meat, fish, egg, whole cereal. B12 Cyanoco-balamin Pernicious anaemia, inflammation of tongue and Meat, eggs, rain water. mouth C Ascorbic acid Scurvy (bleeding of gums), pyorrhea Citrus fruits like orange, lemon, tomato. D Ergocal- ciferol Rickets and osteomalacia Milk, eggs, cod liver oil. E Tocopherol Infertility Oils like cotton seed oil K Phylloquinone Haemophillia Green plants (fat storing) tissues. Water soluble vitamins: The vitamins belonging to group B ( B1,B2 ,B6 ,B12 , etc.) and vitamin C are soluble in water. they are supplied regularly in diet because they are readily excreted in urine and cannot be stored (except vitamin B12 ) in our body. Avitaminosis: Multiple deficiencies caused by lack of more than one vitamin are more common in human beings. This condition of vitamin deficiency is called avitaminosis. Nucleic acids: They are long polymers in which monomeric units are nucleotides which are made up of nitrogen containing hetercyclic base, a pentose sugar and a phosphoric acid residue. Nucleic acids play an important role in transmission of hereditary characteristic and the bio-synthesis of proteins. 7

Nucleosides: A base joined to a sugar molecule is called nucleoside, e.g., adenosine contains adenine and ribose, guanosine contains ribose and guanine. Nucleotides: They are monomers of nucleic acids. They are made up of a heterocyclic base containing nitrogen, a five carbonsugar and a phosphate group, e.g., adenosine monophosphate (AMP),adenosine diphosphate (ADP) and adenosine triphosphate (ATP). They contain P-O-P bonds which are high energy phosphate bonds and due to them nucleotides are energy carries. Ribonucleic acids (RNA): These nucleic acids contain ribose sugar. They contain two bases from purine family, adenine and guanine along with one pyrimidine cystosine. They contain uracil as fourth base. They have single helix structure. RNA helps in biosynthesis of protein. It is associated with the process of learning and memory storage. Deoxyribonucleic acid (DNA): These nucleic acids contain deoxyribose sugar. They contain adenine, guanine, cytosine and thymine base. They have double helix structure of polynucleotides. The two strands of DNA are to be complementary to each other. They are responsible for transferring genetic characteristics. They send information and instruction to the cell for the manufacture of specific protein. Ribose: It is carbohydrate (sugar) containing five carbon atoms. It is present in RNA. Deoxyribose: It is also carbohydrate (sugar) containing five carbon atoms but one oxygen less than ribose. It is present in DNA Structure of Nucleic acids: A unit formed by attachment of a base to 1’ position of sugar is known as nucleoside. The sugars are numbered as 1’ , 2’ , 3’ , in order to distinguish from base. When nucleoside is linked to phosphoric acid at 5’ -position of sugar, we get as nucleotide. Nucleotides are joined together by phosphodiester linkages between 5’ and 3’ carbon atoms of pentose sugar. The formation of nucleotide is shown in figure below. (i) Primary structure: The information regarding the sequence of nucleotides in the chain of a nucleic acid is called its primary structure. (ii) Secondary structure: DNA has double strand structure the two strands are complementary to each other because H - bonds are formed by specific pairs of bases A-T, G-C etc. e.g., base sequence on one straned CGTAATGC. Base sequence on complementary stand is GCATTACG. (iii) Two nucleic acid chains are held together with the help of H- bonds. DNA fingerprinting: i) Every individual has unique fingerprints and used for identification but it can be altered by surgery. ii) The sequence of DNA is unique for a person and information about a person and with the help of DNA is called DNA fingerprinting. iii) It is used in forensic labs for identification of criminals. iv) It is used in paternity test. v) It is used in identification of unclaimed dead bodies. vi) It is used to identify racial group. Functions of nuclear acids (i) Replication : The process by which a single DNA molecule produces two identical copies of itself is called cell division (mitosis) or replication. (ii) It transfers genetic characters. (iii) Synthesis of protein: Another important function of DNA is the synthesis of proteins. Infact, DNA may be regarded as the instruction manual for the synthesis of all proteins present in a cell. It takes place in the following two steps: (i) Transcription and (ii) Translation 1. Transcription: It involves copying of DNA base sequences into a RNA molecule called the messenger RNA (m RNA). 2. Translation: The mRNA directs protein synthesis in the cytoplasm of the cell with the help of rRNA and tRNA. This process is called translation. 3. Codon: The specific ribonuchotide sequence in mRNA forms a code that determines the order in which the different amino acid residues have to be joined. The four bases in the m RNA, i.e., A, C, G and U act in form of triplets. Since a particular triplet codes a specific amino acid, therefore, these triplets are called codons. 8

4. Genetic code: Each segment of a DNA molecule which codes for a specific protein or polypeptide is called a gene and thus every protein in a cell has corresponding gene. The relation between the nucleotide triplets and the amino acids is called the genetic code. 5. Mutations: A mutation may be defined as a chemical change in the sequence of nitrogenous bases along the DNA strands that can lead to the synthesis of proteins with altered amino acid sequence. 9