Biomolecules PDF

Biomolecules INTRODUCTION y Living systems are made up of various Definitions complex biomolecules like nucleic acids, carbohydrates, proteins, lipids, etc. Chemically, the carbohydrates y Carbohydrates and proteins are essential may be defined as optical...

Biomolecules INTRODUCTION y Living systems are made up of various Definitions complex biomolecules like nucleic acids, carbohydrates, proteins, lipids, etc. Chemically, the carbohydrates y Carbohydrates and proteins are essential may be defined as optically constituents of our food. active polyhydroxy aldehydes y In addition, some simple molecules like or ketones or the compounds mineral salts and vitamins also play an which produce such units on important role in the functions of organisms. hydrolysis. CARBOHYDRATES y Carbohydrates (hydrates of carbon) are naturally occurring compounds having general formula Cx(H2O)y, which are constantly produced in nature & participate in many important bio-chemical reactions. Ex. Glucose C6H12O6 C6(H2O)6 Fructose C6H12O6 C6(H2O)6 Concept Ladder Cellulose and Starch (C6H10O5)n y Sucrose (Cane sugar) – C12H22O11, and Maltose Saccharin is not (Malt Sugar) C12(H2O)11 carbohydrate but is y But some compounds which have formula 500 times sweeter than according to Cx(H2O)y are not known as sucrose. carbohydrate Ex. CH2O Formaldehyde C2(H2O)2 Acetic acid C3(H2O)3 Lactic acid y There are many compounds, which shows chemical behaviour of carbohydrate but do not confirm the general formula Cx(H2O)y such as – C5H10O4 (2-deoxyribose) C6H12O5 (Rahmnose) Previous Year’s Questions y Carbohydrates, the energy source of living beings, are the most abundant organic Whcih of the following is the compound around us. sweetest sugar? y In metabolic process in the living beings, [AIPMT] glucose is usually oxidized into carbon dioxide (1) Fructose (2) Glucose and water to provide energy to the cell for (3) Sucrose (4) Maltose Biomolecules their functioning. 1.  Classification of Carbohydrates Carbohydrates are classified on the basis of their behaviour on hydrolysis. Monosaccharides (simple sugars) y These are the sugars which cannot be hydrolysed into smaller molecules. General formula is CnH2nOn. y About twenty monosaccharides are known to exist in nature. Some examples are fructose, Concept Ladder glucose, ribose, etc. y If −CHO group is present in monosaccharide, Glucose — grape sugar or dextrose. then it is known as aldose. Fructose — fruit sugar. − C− Lactose — milk sugar. y If || group is present in monosaccharide, O then it is known as ketose. Carbon atoms General term Aldehyde Ketone 3 Triose Aldotriose Ketotriose 4 Tetrose Aldotetrose Ketotetrose 5 Pentose Aldopentose Ketopentose Biomolecules 6 Hexose Aldohexose Ketohexose 7 Heptose Aldoheptose Ketoheptose 2. Oligosaccharides y These are the sugars which yields 2-10 Concept Ladder monosaccharides units on hydrolysis. y When two monosaccharide units obtained A group of polysaccharides y On hydrolysis of a disaccharide, they may be which are not so widely the same or different. used in nature is pentosans For example, Hydrolysis (C5H8O4)n Monosaccharides. Sucrose → Glucose + Fructose (a) Disaccharides : Two monosaccharide unit on hydrolysis (may or may not be same). Ex. Sucrose, Maltose (b)Trisaccharides : Three monosaccharide unit on hydrolysis. Polysaccharides y These are the non-sugars which yield a large no of monosaccharide units on hydrolysis. y Polysaccharides are the carbohydrates Rack your Brain which on hydrolysis yields a large number of monosaccharide units. y Polysaccharides are not sweet in taste, hence What is invert sugar and why is it they are also called non-sugars. so named? y General formula – (C6H10O5)n. Ex. Starch, Cellulose, Glycogen etc. Reducing and Non-Reducing Sugars y Those sugars or carbohydrates which reduce Fehling’s solution and Tollens reagent are referred to as reducing sugars. y All monosaccharides whether aldose or ketose are reducing sugars. y In disaccharides, when the reducing groups of monosaccharides, that is, aldehydic or ketonic Previous Year’s Questions groups, are bonded, then these are referred to as non reducing sugars. e.g., sucrose. Which one given below is a non- reducing sugar? GLUCOSE [NEET(I)-2016] y Glucose occurs in both free and combined (1) Glucose (2) Sucrose Biomolecules forms in nature. (3) Maltose (4) Lactose y It is present in honey and sweet fruits. 3.  y Also, glucose is present in large amounts in ripe grapes, so it is known as grapes sugar. Rack your Brain y Glucose is the unit of starch, cellulose and glycogens. Fructose contain a keto group but still it reduces Tollens’ Preparation of Glucose reagent. Why? (1) From Sucrose (Cane sugar) y Fructose and glucose are obtained in equal amounts when sucrose is boiled with dil. HCl or H2SO4 in alcoholic solution. + H C12H22O11 + H2O → C6H12O6 + C6H12O6 Sucrose Glucose Fructose (2) From Starch y Glucose is obtained commercially by the Concept Ladder hydrolysis of starch by boiling it at 393 K with dil. H2SO4. The carbonyl group of (C6H10O5 )n + H + nH2O  393 K; 2−3 atm → nC6H12O6 aldoses and ketoses can Glucose be reduced by the usual Starch or cellulose carbonyl-group reducing Structure of Glucose agents (eg., NaBH4). The y Glucose is aldohexose and is also called product of the reduction is dextrose. a polyalcohol, known as an y Glucose is a monomer of many of the larger alditiol. carbohydrates, namely cellulose, starch. y It is considered to be present in large amounts as an organic compound on earth. y C6H12O6 is its molecular formula. Previous Year’s Questions Reactions of Glucose Sucrose on hydrolysis gives (1) Oxidation [NEET-2020] y Dicarboxylic acid, saccharic acid can be (1) b-D-glucose + a-D-fructose yielded by oxidizing both glucose as well as gluconic acid with nitric acid. (2) a-D-glucose + b-D-glucose Biomolecules y This indicates the presence of a primary (3) a-D-glucose + b-D-fructose alcoholic (–OH) group in glucose. (4) a-D-fructose + b-D-fructose 4.  Previous Year’s Questions Fructose reduces Tollens’ reagent due to [AIPMT-2010] (1) Asymmetric carbons (2) Primary alcoholic group (3) Secondary alcoholic group (4) Enolisation of fructose followed by conversion to aldehyde by base. Rack your Brain A monosaccharide has a molecular weight of 150. Also itwas not optically active. What is the structure of monosaccharide? y Fisher gave the exact spatial arrangement of different — OH groups. Structure I represent the spatial arrangement, and structures II and III represent gluconic acids. Concept Ladder The change in specific rotation of an opticaly active compound in solution with time to an equilibrium alue is called Biomolecules mutarotation. 5.  (2) Reduction y On prolonged heating with HI, there is Concept Ladder formation of n-hexane (Straight Chain). Glucose in aqueous solutin is reduced with sodium amalgam to hexahydric alcohol sorbitol. Rack your Brain What is the product formed on (3) Cyanohydrin Formation y It gives cyanohydrin when added a molecule oxidation of glucose with mild of hydrogen cyanide. oxidizing agent such as Br2 water? (4) Oxime Formation Previous Year’s Questions y To form an oxime glucose is reacts with hydroxylamine. Glucose molecule reacts with X number of molecules of phenyl hydrazine to yield osazone. the value of X is [AIPMT] Biomolecules (1) two (2) one (3) four (4) three 6. (5) Reaction with phenylhydrazine (formation of osazone) Rack your Brain What is the product formed when glucose react with excess amount of phenyl hydrazine? (6) Acetylation y Glucose pentaacetate is formed by Acetylation of glucose with acetic anhydride; this also confirms the presence of five –OH groups. y Five –OH groups should be attached to Concept Ladder different carbon atoms. Glucose pentaacetate cannot be converted into the open chain form because its anomeric hydroxyl group (i.e. C1–OH) is acetylated and hence Stereochemistry of Carbohydrates does not form the oxime. D & L Sugars Aldotriose (Smallest carbohydrate) Ex. Fischer projection Definition The series of aldoses or ketoses in which the configuration of the penultimate C-atom (C-next to CH2-OH group) is described as D-sugars if -OH is towards RHS Biomolecules & L-sugars if it is towards LHS. 7.  Aldotetros Types of Aldotetrose (i) Erythrose (ii) Threoese No. of C* = 3 (in Aldopentose) No. of optical isomers 23 = 8 No. of D Sugars = 4 no. of L-Sugars = 4 D-Aldopentose Biomolecules All Isomeric D-Sugars are diastereomers. 8. Aldohexose No. of C* = 4 No. of stereoisomers = 24 = 16 No. of D-sugars = 8 No. of L-sugars = 8 Cyclic Structure of Glucose Concept Ladder The structure of glucose explained most of its properties but the following reactions and The two cyclic hemiacetal facts could not be explained by this structure. forms of glucose differ y The pentaacetate of glucose does not react only in the configuration of with hydroxylamine it is indicated by the the hydroxyl group at C1, absence of free —CHO group indicates. called anomeric carbon. y a and b are the names of two different Such isomers, i.e., a-form crystalline forms of glucose. and b-form, are called anomers. a-D(+) Glucose The a-form of glucose (m.p. 419 K) is obtained by crystallisation from concentrated solution of glucose at 303 K. Previous Year’s Questions b-D(+) Glucose a-D-glucose and b-D-glucose The b-form (m.p. 423 K) is obtained by are crystallisation from hot and saturated [AIPMT] aqueous solution at 371 K. (1) Epimers (2) Anomers (3) Enantiomers (4) Diastereomers Biomolecules 9.  Howarth Structure y Pyranose structure is a six-membered cyclic Previous Year’s Questions structure of glucose (α– or β–), in analogy with pyran. Which one of the following does y Pyran is a cyclic organic compound with five not exhibit the phenomenon of carbon atoms and one oxygen atom in the mutarotation? ring. [AIPMT] y The Haworth structures given below are the (1) (+)-Sucrose (2) (+)-Lactose cyclic structure of glucose. (3) (+)-Maltose (4) (-)-Fructose FRUCTOSE y Fructose is an important ketohexose. It also has the molecular formula C6H12O6. y It is obtained by the hydrolysis of disaccharide. Hydrolysis Ex : Sucrose → Glucose + Fructose Concept Ladder y It is a natural monosaccharide found in vegetables, fruits and honey. All the monosaccharides, Structure of Fructose whether aldoses y Based on its reactions, it was found that and ketoses, in their in the case of glucose contained at carbon hemiacetal and hemiketal forms behave as reducing Biomolecules number atom two, a ketonic functional group is present and six carbons in a straight chain. carbohydrates. 10.  It is a laevorotatory compound and belongs to D-series. It is appropriately written as Concept Ladder D-(–)-fructose. D-fructose exists in two stereoisomeric forms, i.e., a-D-fructopyranose and b-D-fructopyranose. Cyclic Structure of Fructose y This structure is obtained by the addition of —OH at C5 to the ketonic group, which produce two cyclic forms. Howarth Structure y The ring has an analogy to the compound furan and is a five-membered ring. It is a five- membered cyclic compound with one O and four C atoms. Biomolecules 11.  Comparison of Glucose and Fructose S.NO. Property Glucose Fructose 1 Molecular formula C6H12O6 C6H12O6 2 Nature Polyhydroxy aldehyde Polyhydroxy ketone 3 Melting point 146°C 102°C 4 Optical nature Dextro rotatory Levo rotatory 5 Molisch test Violet colour Violet colour 6 Tollen’s reagent Silver mirror Silver mirro 7 Fehling’s solution Red ppt Red ppt 8 Phenyl hydrazine Forms osazone Forms osazone Mixture of glycolic Oxidation by acid, Tartaric acid and 9 Saccharic acid conc. HNO3 Trihydroxy Gluteric acid DISACCHARIDES y By the loss of a water molecule, an oxide linkage is formed, which joins two monosaccharides. y These two monosaccharides are held together by glycosidic linkage (oxide linkage) through Rack your Brain oxygen atom. Biomolecules Are all disaccharides sugars? 12. y The reducing groups (aldehydic or ketonic) of monosaccharides are bonded in disaccharides. Concept Ladder Therefore these are non-reducing sugars, e.g., sucrose. y Whereas sugars in which these reducing Sucrose is an naturally groups are free, which are called reducing occurring sugar found sugars, for example, lactose and maltose. in various amounts in plants like fruits and also (1) Sucrose produced commercially y On hydrolysis of sucrose, the equimolar from sugar cane and sugar mixture of D(+) glucose and D(-) fructose are beets. formed. + H C12H22O11 + H2O → C6H12O6 + C6H12O6 Sucrose D(+)-Glucose D(–)-Fructose y By a glycosidic linkage between C1 of a-D- glucose and C2 of b-D-fructose, these two monosaccharides can be held together. y Sucrose is a non-reducing sugar as the reducing groups of glucose and fructose is involved in the formation of a glycosidic bond. Previous Year’s Questions Which one of the following sets of monosaccharides forms sucrose? [AIPMT-2012] y It is dextrorotatory, but after hydrolysis, it gives (1) a  -D-galactopyranose and laevorotatory fructose and dextrorotatory a-D-glucopyranose glucose. (2) a  -D-glucopyranose and b-D- y Since the dextrorotation of glucose (+ 52.5°) fructofuranose is less than laevorotation of fructose (–92.4°), (3) b  -D-glucopyranose and a-D- hence the mixture is laevorotatory fructofuranose (4) a  -D-glucopyranose and b-D- Biomolecules y Invert sugar is the product formed when there is change in the sign of rotation, from dextro fructofuranose (+) to laevo (–) after the process of hydrolysis of sucrose. 13.  (2) Maltose y It maltose C1 of one glucose (I) is linked to Concept Ladder C4 of another glucose unit (II) of two a-D- glucose units. Maltose can be broken y In solution, C1 of second glucose produce down to glucose by the a free aldehyde group, and it is a reducing maltase enzyme, which sugar as it has reducing properties. catalyses the hydrolysis of the glycosidic bond. Rack your Brain Is maltose sweeter than glucose? (3) Lactose y Lactose is found in milk so it commonly known as milk sugar. y It is composed of β-D-galactose and β-D- glucose. y It has a linkage between C1 of galactose and C4 of glucose. It is considered as reducing sugar as free aldehyde group may be produced at C1 of glucose unit. Concept Ladder Unabsorbed lactose passing through the intestinal tract with little lactase causes colic (severe pain in the stomach and bowels) diarrhoea and other interstinal problems. This is called lactose intolerance. This happens in older people. Biomolecules 14. POLYSACCHARIDES y When a large number of monosaccharide Concept Ladder units linked together by glycosidic linkages, polysaccharides are formed. They generally Starch is a non-reducing act as the food storage or structural materials. saccharide. it neither reduces Tollens’ reagent (1) Starch (or Fehling’s solution) nor y It is the main storage polysaccharide of forms an osazone. plants. y High content of starch is found in some vegetables, roots, tubers and cereals hence, it is the most important dietary source for human beings. y It is a polymer of alpha- glucose and consists of two components—Amylopectin and Amylose. Rack your Brain Amylose y Amylose constitutes about 15-20% of starch What is the inclusion complex? and is water soluble component. y Amylose is formed chemically formed by 200- 1000 a-D-(+)-glucose units held together by C1–C4 glycosidic linkage, forming long unbranched chain. Amylopectin y Amylopectin is constitutes about 80- 85% of starch and is not soluble in water. y In it, a chain is formed by C1–C4 glycosidic Biomolecules linkage, while branching occurs by C1– C6 glycosidic linkage. It is formed by the branched-chain polymer of a-D-glucose units. 15.  (2) Cellulose y Cellulose is present mostly in plants and is the most abundant organic substance in the whole plant kingdom. It is found mostly in Previous Year’s Questions the cell wall of plant cells. y It is composed only of a-D-glucose units and Cellulose is polymer of is a straight chain polysaccharide , which [AIPMT] are linked together by the glycosidic linkage (1) Glucose (2) Fructose between C1 of one glucose unit and C4 of the (3) Ribose (4) Sucrose next glucose unit. Q1 What are disaccharides? Give one example. Sol. Disaccharides on hydrolysis give two molecules of the same monosaccharides. For example, sucrose, maltose, lactose, etc. or different Q2 Which of the two components of starch is water soluble? Sol. Amylose is water soluble but amylopectin is water insoluble. Biomolecules 16.  Concept Ladder Excess glucose gets stored in the liver as glycogen or, with the help of insulin, converted into fatty acids, circulated to other parts of the body and stored as fat in adipose tissue. Rack your Brain (3) Glycogen y In animal body glycogen is stored in the form Why is glucose stored as of carbohydrates. glycogen ? y Its structure is similar to amylopectin that’s why it is also known as animal starch and is rather more highly branched. y It is present in brain, muscles and liver. Enzymes break the glycogen down to glucose whenever body wants glucose. Q3 What is Molisch test? Explain. Sol. All carbohydrates, i.e., monosaccharides, oligosaccharides and polysaccharides are characterised by Molisch test. A 1% alcoholic solution of a-naphthol is called Molisch reagent. When Molisch reagent is added to an aqueous solution or suspension in water of a carbohydrate followed by conc. H2SO4 along the Biomolecules sides of the test tube, a violet ring is formed at the junction of the two layers. 17.  y Glycogen is also found in fungi and yeast. Reducing/ Carbohydrates Type Units Linkage Non Reducing Glucose Monosaccharide Reducing Glucose — Fructose Monosaccharide Reducing Fructose — C1 of a-D-Glucose Glucose Sucrose Disaccharide Non Reducing and b-D- and C2 of Fructose Fructose a-1, 4’ Both are Maltose Disaccharide Reducing glycosidic a-D-Glucose linkage b-D-Glucose a-1, 4’ Lactose Disaccharide Reducing and b-D- glycosidic Galactose linkage a-1, 4’ Amylose + and a-1, 6’ Starch Polysaccharide Non Reducing Amylopectin glycosidic linkage b-1, 4’ Cellulose Polysaccharide Non Reducing b-D-Glucose glycosidic linkage a-1, 4’ and a-1, 6’ Glycogen Polysaccharide Non Reducing Amylopectin glycosidic linkage Importance of Carbohydrates y In life of both plants and animals they are Biomolecules essential as they form a large portion of our food. y In ayurvedic of medicine, honey has been 18.  used for a long time as an instant source of energy. Concept Ladder y Starch and glycogen form of these areused as storage molecules in plants and animals Cellulose is commonly respectively. used in foods and bakery y Cell wall of plants and bacteria is made from formulations as a source of cellulose. dietary fiber or to improve y They provide various raw materials for many their texture. It is also used important industries like paper, textiles, as a bulking agent in low- lacquers and breweries. calorie and gluten-free baked products. PROTEINS y Brezeliues introduced the term protein which means first (Proteios = first). y They are the most abundant biomolecules of the living system. Chief sources of proteins are cheese, milk, pulses, peanuts, etc. y They form the fundamental basis of structure and functions of life. They are present in every part of the body. y They are also required for maintenance and Rack your Brain growth of body. y It is derived from Greek word, “proteins” which means primary or of prime importance. What is the monomer unit of y All proteins are polymers of α-amino acids. protein? Amino Acids y Amino acids are carboxylic acids having an –NH2 group. When the –NH2 group is at α-position these are called α-amino acids. NH2 | R − CH − COOH α-amino acid y Amino acids can be categorized as a, b, g, d Previous Year’s Questions and so on, it depends on the relative position of amino group with respect to carboxyl Which of the following is a basic group. Only α-amino acids are obtained on amino acid? hydrolysis of proteins. They also can contain [NEET-2020] Biomolecules (1) Serine (2) Alanine (3) Tyrosine (4) Lysine 19.  other functional groups. y The property of the compond or its source Rack your Brain are reflected by their trivial names. y Glycine is so-called as it has a sweet taste, Lack of essential amino acids and tyrosine (in Greek, tyros means cheese) in the diet leads to the disease was first obtained from cheese. called? y Amino acids are generally represented by a 3 letter symbol, sometimes 1 letter symbol is also used. Classification of Amino Acids y On the basis of relative no. of carboxyl and amino groups in their molecule, they are classified as acidic, basic or neutral. (1) Neutral : Equal number of carboxyl and amino groups makes it neutral (2) Basic : More number of amino than carboxyl Concept Ladder groups makes it basic (3) Acidic : More carboxyl groups as compared to amino groups makes it acidic. Nonessential amino acids support tissue growth and Non-essential Amino Acids repair, immune funciton, y Non-esseitial amino acids are defined as the red blood cell formation, type of amino acids, which can be synthesised and hormone synthesis. in the body. Essential Amino Acids y Essential amino acids are defined as the type of amino acids, which cannot be synthesized in the body and must be obtained by the diet. y Their deficiency causes Kwashiorkor, a disease. Examples of essential amino acids include, valine, lucine, isolucine, lysine, threonil, phenyl Previous Year’s Questions alanine methionyl, tryptophan, histidine and arginine. The non-essential amino acid among the following is [NEET-2019] Biomolecules (1) Lysine (2) Valine (3) Leucine (4) Alanine 20.  Name of the Characteristic feature Three letter One letter S.No. Amino Acids of side chain. R symbol of code 1 Glycine H Gly G 2 Alanine —CH3 Ala A 3 Valine* (H3C)2CH— Val V 4 Leucine* (H3C)3CH—CH2— Leu L 5 Isoleucine* H3C − CH − CH − Ile I | CH3 6 Arginine* NH =C− NH − CH2 | ( )3 − Arg R NH2 7 Lysine* ( H2N − CH2 )4 − Lys K 8 Glutamic acid HOOC—CH2—CH2— Glu E 9 Aspartic acid HOOC—CH2— AsP D 10 Glutamine O Glu Q || H2N − C− CH2 − CH2 − 11 Asparagine O Asn N || H2N − C− CH2 − 12 Threonine* H3C—CHOH— Thr T 13 Serine HO—CH2— Ser S Biomolecules 21.  Name of the Characteristic feature Three letter One letter S.No. Amino Acids of side chain. R symbol of code 14 Cysteine HS—CH2— Cys C 15 Methionine* H3C—S—CH2—CH2— Met M 16 Phenylalanine* C6H5—CH2— Phe F 17 Tyrosine (p)HO—C6H5—CH2 Tyr Y 18 Tryptophan* Trp W 19 Histidine* His h 20 Proline Pro P *Essential amino acids Previous Year’s Questions Charactertic Features of Amino Acids y Amino acids are generally colourless, Which of the following comopund crystalline solids. can form a zwitter ion? y These are water-soluble and have high [NEET-2018] melting point. (1) Aniline (2) Acetanilide (3) Benzoic acid Biomolecules y These are behave like salts rather than simple amines or carboxylic acids. This behaviour is (4) Glycine 22.  due to the presence of both basic (amino group) and acidic (carboxyl group) groups in Rack your Brain the same molecule. Glycine exists as a zwitter ion Zwitter Ion but o- and p-aminobenzoic y In aqueous solution, amino group can accept acids not exists. Why? a proton and the carboxyl group can lose a proton, which give rise to a dipolar ion termed as zwitter ion. y Zwitter ion contains both positive and Concept Ladder negative charges but is neutral in nature. y As a-carbon atom is asymmetric; therefore, all other naturally occurring a-amino acids pH at which there is no are optically active, except glycine. These net migration of the amino exist both in ‘D’ and ‘L’ forms. L-configuration acid under the influence of is the most naturally occurring amino acid. an applied electric field is L-Amino acids are represented by writing the called isoelectric point. –NH2 group on the left-hand side. Peptide bond or Peptide Linkage Peptides are those amides which are formed due to condensation between 2NH2 group and–COOH group of two different amino acids. y The –CO–NH– bond is called peptide linkage or bond. The >C=O group of an amide is sp2 hybridised with coplanar structure. Previous Year’s Questions In a protein molecule various amino acid are linked together by [AIPMT-2012] y To eliminate water molecule and form (1) Peptide bond peptide bond —CONH—, the combination of (2) Dative bond the amino group of one molecule with the (3) a-glycosidic bond Biomolecules carboxylic group of other, there is a reaction (4) b-glycosidic bond between two molecules of similar or different 23.  amiono acids The product of the reaction is made up of two amino acids; hence it is Rack your Brain termed dipeptide. For example, What is the peptide bond? when carboxyl group of glycine combines with the amino group of alanine we get a dipeptide, glycylalanine. y An amino acid unit having a free NH2 group is known as N-terminal amino acid while an amino acid with a free –COOH group is known as C-terminal amino acid. y N-terminal amino acid residue in a protein is determined by Sanger (1-fluoro-2, 4-dinitrobenzne) or DNP (2, 4-dinitrophenyl) method. y C-terminal amino acid residue in a protein is determined by hydrazinolysis. Concept Ladder y When writing the structure of peptides, the N terminal end is taken on left hand side while, An alkaline solution of a C-terminal end is at right hand side. protein or a polypeptide when treated with a few drops of 1% CuSO4 solution, produces a violet colouration. The colour is due to the formation of a coordination complex of y A tripeptide contains 3 amino acids linked by Cu2+ with >C=O and -NH 2 peptide linkages, therefore it can be form if groups. a 3rd amino acid combines to a dipeptide. y When 4, 5 or 6 amino acids are linked, the respective products are termed as tetrapeptide, pentapeptide or hexapeptide. Biomolecules 24.  When the no. of such amino acids is more than 10, then the products are known as Previous Year’s Questions polypeptides. In a protein molecule various amino acids are linked together by [AIPMT] (1) peptide bond (2) dative bond y Protein is defined as a polypeptide with (3) a-glycosiddic bond more than 100 amino acid residues, having (4) b-glycosidic bond molecular mass higher than 10,000 u. Classification of Proteins They can be classified into 2 types on the basis of their molecular shape. (1) Fibrous Proteins y When the polypeptide chains are held Rack your Brain together by H and S2 bonds and run parallel, then fibre – like structure is formed. What is snake venom made of? y Proteins are generally insoluble in water and are quite stable against a moderate change in temperature and pH value. Ex : keratin (present in hair, wool, silk) and myosin (present in muscles), etc. (2) Globular Proteins y In such proteins, the polypeptide intramolecular chains get folded to give Concept Ladder a spheroidal shape due to intramolecular hydrogen bonding, van der Waals forces, dipolar interaction and disulphide bridging. Polypeptides are These are usually soluble in water and change amphoteric in character with a change in temperature and pH. because of the presence Ex : Insulin, ,albumins, Enzyme, haemoglobin and of terminal ammonium and antibodies. carboxylate ions as well as the ionized side chains of amino acid residues. Biomolecules 25.  Hydrolysis of Proteins Proteins can be hydrolysed and on the basis Previous Year’s Questions of hydrolysis they are of following types. (1) Simple Proteins : On hydrolysis they give only Which is the correct statement? a-amino acids [AIPMT] Ex :Albumins, globulins etc. (1) Starch is a polymer of (2) Conjugated Proteins : These are having a Non- a-glucose protein Prosthetic group and on it’s bases (2) Amylose is a compoonent of they are of following types. cellulose (a) Nucleo protein : Here Prosthetic group. is (3) Proteins are comopsed of only nucleic acid. e.g., Nuclein one type of amino acid (b) Glycoprotein : Here Prosthetic group is (4) In cyclic structure of fructose, any carbohydrate. e.g., Mycin there are four carbons and one (c) Chromo protein : Here Prosthetic group is oxygen atom. any pigment having metals like Fe, Cu, etc. Ex : Haemoglobin, Chlorophyll. (3) Derived Protein : They are achieved by the partial hydrolysis of simple conjugated proteins. Ex : Proteoses, Peptones. Structure of Proteins Rack your Brain Amino acids are joined together by an amide linkage called peptide bond. Proteins are long What is the disease caused by polymers of amino acids linked by peptide defective heamoglobin molecule bonds (polypeptides) in which one of the glutamic acid (1) Primary Structure molecule is replaced by valine? y Frederic Sanger gave Primary structure of Insulin for the first time. y Proteins may have one or more than one polypeptide chains. y Amino acids of each polypeptide in a protein Previous Year’s Questions are joined to each other in a specific sequence and this sequence is termed as primary The helical structure of protein is structure of that protein. stabilised by (2) Secondary Structure [AIPMT] y By intramolecular H-bonding between the (1) Dipeptide bonds carboxyl and amino groups there is regular (2) Hydrogen bonds folding of the backbone of the polypeptide (3) Ether bonds Biomolecules chain which arises secondary structure. (4) Peptide bonds 26. y Secondary structures are found to present in two different types of structures viz. a-helix Rack your Brain and b-pleated sheet structure. y By intramolecular H-bonding between — Which types of bonds are CO— and —NH— groups of the peptide bond responsible for the stability of there is regular folding of the backbone of a-helix? the polypeptide chain which aries a-helix and b-pleated sheet structures. (a) a-Helix Structure y α-Helix is one of the most common ways in which a polypeptide chain forms all possible hydrogen bonds by twisting into a right handed screw (helix) with the –NH group of each amino acid residue hydrogen bonded to the >C=O of an adjacent turn of the helix. y Stabilization of an α-helical configuration by hydrogen bonding. Ex : α-keratin in skin, nails, myosin in muscles, fibroin in silk. α-Helix is called 3.6 helix as each turn of helix has 3.6 amino acids and a 13-membered ring. (b) b-pleated sheet structure y In β-pleated sheet structure all peptide chains are stretched out to nearly maximum extension and then laid side by side which are held together by intermolecular hydrogen Biomolecules bonds. 27.  y When the size of the groups (Alkyl Group) is moderate, the polypeptide chains contract a little to give a β-pleated sheet structure to protein molecule, as in silk protein fibroin. y β-pleated sheet structure are parallel and Anti parallel type. y In parallel form all polypeptide chain run in the same direction while in Anti parallel form, the alternate Polypeptide chain run in same direction. Ex : Parallel conformation — Keratin in hair  Anti–Parallel Conformation — Silk Protein fibroin (3) Tertiary Structure y The tertiary structure of proteins represents the folding of the polypeptide chains or folding of the secondary structure of proteins. Concept Ladder y Tertiary and secondary structures of proteins are stabilise by the forces of H-bonds, disulphide linkages, van der Waals and The tertiary structure is electrostatic forces of attraction. the three-dimensional y It gives rise to 2 major molecular shapes that structure of globular is fibrous and globular. proteins. It arises due to the folding and (4) Quaternary Structure superimposition of various y Some of the proteins are composed of more secondary structural than one polypeptide chains referred to as elements. sub-units. y When these subunits have spatial arrangement with respect to each other then they are termed as quaternary structure. Ex : Haemoglobin is an aggregate of four sub-units, Previous Year’s Questions two identical α-chains (having 141 Amino acid residues and two identical β-chains (having Hemoglobin is 146 Amino acid residues). [AIPMT] (1) A vitamin (2) A carbohydrate (3) An Enzyme Biomolecules (4) A globular protein 28. Denaturation of Proteins y Disruption of the native conformation of a protein will cause the protein to loose its biological activity. This is called denaturation. y Various changes in the surroundings of a protein such as pH, temperature, presence of salts or certain chemical agents can disrupt the complex three-dimensional structure Previous Year’s Questions (conformation) of the proteins. y Due to physical and chemical changes, the Which structure(s) of proteins H-bonds are disturbed. remain(s) intact during Ex :(i) On boiling an egg the albumin get denaturation process? coagulated. [NEET-2019] (ii)  During formation of cheese from milk, (1) Both secondary and tertiary the globular protein lactalbumin becomes structure fibrous. (2) Primary structure only Biomolecules (3) Secondary structure only (4) Tertiary structure only 29.  Detection of Protein (1) Millon’s test: Aqueous solution of protein Concept Ladder (except tyrosine) gives a white precipitate with millon’s reagent (Mercurous nitrate and The most widely used mercuric nitrate in HNO2 ). method for determining (2) Xantho protein test: Here, protein having the N-terminal amino acid tyrosine and phenyl alanine amino acids give residue in a protein or a a yellow colour when tested with conc. HNO3 polypeptide molecule is (3) Nin-hydrin test: Protein on boiling with called the DNP-method or dilute aqueous solution of nin-hydrin (2, Sanger’s method. 4-dihydroxy indane-1, 3-dione) gives blue violet colouration. (4) Biuret test: Alkaline solution of proteins gives violet colouration with 1% copper sulphate solution due to formation of a complex between Cu2+ and the peptide linkage. LIPIDS y Lipids are generally not soluble in water y Lipids are simple fatty acids. Carboxyl group Rack your Brain attached to an R group form fatty acids, it can be ethyl (–C2H5), or methyl (–CH3) or What is difference between lipid higher number of –CH2 groups (1 carbon to 19 and fat? carbons). Ex : (i) palmitic acid has 16 carbons including carboxyl carbon. (ii) Arachidonic acid contains twenty carbon atoms which includes the carboxyl carbon. y Fatty acids contains saturated (without double bond) or unsaturated groups(with one or more than one C=C double bonds). y Glycerol is another simple lipid which is Previous Year’s Questions trihydroxy propane. y Both glycerol and fatty acids makes many The cell membranes are mainly lipids. Fatty acids are found esterified with composed of glycerol, therefore they can be monoglycerides, [AIPMT] diglycerides and triglycerides. (1) Fats y Oils have lower M.P. (e.g., gingelly oil) and (2) Proteins hence remain as oil in winters. These are also (3) Phospholipids Biomolecules called oils and fats based on melting point. (4) Carbohydrates 30. y Phospholipids are some lipids containing phosphorous and a phosphorylated organic compound in them. Lecithin is one example. They are found in cell membrane. y Some tissues especially the neural tissues have lipids with more complex structures. ENZYMES y The biological catalysts which can increase the rate of biochemical reactions even under mild conditions of temperature and pH of Concept Ladder living organisms are termed as enzymes. y Enzymes are chemically similar to globular Iodine number is no. of proteins. grams of I2 that combines y They are very specific for each reaction and with 100 g of fat or oil. It is for every substrate. used to measure extent of y They are usually named after the compound unsaturation in oil or fat. or group of compounds upon which they work. Ex : The enzyme that catalyses hydrolysis of maltose into glucose is named as maltase Maltase C12H22O11  → 2 C6H12O6 Maltose Glucose Previous Year’s Questions y After the reaction enzymes are also Enzymes are made up of mentioned, where they are used. [AIPMT] Ex :Oxidoreductase enzymes are the enzymes (1) Edible proteins which can catalyse the oxidation of one (2) Proteins with specific substrate and simultaneously reduce another structure substrate. (3) Nitrogen containing y They are very specific in their action on carbohydrates Biomolecules substrates and each enzyme catalyses only a (4) Carbohydrates specific type of reaction. 31.  y They are active at moderate temperature (310 K), neutral pH (7) and 1 atmospheric pressure. Concept Ladder y The action of enzymes are inhibited by various organic and inorganic molecules Protein co-factor complex called inhibitors. is called holoenzyme while y The activity of enzymes can be increased by the inactive protein part is metal ions and smaller organic molecules apoenzyme. called coenzymes or cofactors. For example, Holoenzyme ⇌Apoenzyme inorganic ions, Mg2+, Mn2+, Fe2+, Co2+, Cu2+ , + cofactor organic molecules like vitamins (thiamine, riboflavin). Mechanism of Enzyme Action y For the progress in reaction enzymes are needed only in small quantities. y Enzymes function by lowering the energy of activation of a particular reaction. Ex : F  or sucrose the activation energy for acid hydrolysis is 6.22 kJ mol–1, whereas when it is hydrolysed by the enzyme its activation Rack your Brain energy is only of 2.15 kJ mol–1. which is cause of albinism? Concept Ladder Enzyme streptokinase is used to dissolve blood clot in coronary artery (which is Biomolecules cause of heart attack). 32. Lock and Key Hypothesis y A number of cavities are present on the Rack your Brain surface of enzymes. These cavities have specific shapes and groups like –NH2 –COOH, Urea’s enzyme can catalyse –OH etc. hydrolysis of urea but not of y These are active centres on enzyme surfaces. n-methyl urea. Why? y Here ‘key’ (reagent or substrate) fits in the ‘lock’, that is, the active site of catalyst to give an intermediate complex, which changes into product and the enzyme catalyst is released. R   E + S   E − S → E +P Activated complex S.No. Enzyme Enzymatic Reaction (i) Invertase or sucrose Sucrose → Glucose + Fructose (ii) Maltase Maltose → Glucose + Glucose (iii) Lactose Lactose → Glucose + Galactose (iv) a-Amylase Starch → n × Glucose (v) Pepsin Proteins → a-Amino acids (vi) Trypsin Proteins → a-Amino acids (vii) Nucleases DNA or RNA → Nucleotides (viii) DNA polymerase Deoxynucleotide triphosphates → DNA Biomolecules (ix) RNA polymerase Ribonucleotide triphosphates → RNA 33.  VITAMINS y They are the organic compounds which are Definition required in small amounts in our diet but their deficiency causes specific diseases. organic compounds required y Plants can synthesise almost all of vitamins in the diet in small amounts but most of the vitamins cannot be to perform specific biological synthesised in our body. functions for normal y Some of vitamins produce by bacteria of the maintenance of optimum gut. growth and health of the y Vitamins are categorised by alphabets A, B, C, organism. D, etc. Some of them are further termed as sub-groups e.g. B1, B2, B6, B12, etc. Classification of Vitamins y On the basis of their solubility in H2O or fat they are classified into two groups. Rack your Brain (i) Fat Soluble Vitamins Which vitamin is not found in y Vitamins which are soluble in oils and fats plants? but not soluble in water are to be considered in this group. y They are vitamins A, D, E and K. These can be stored in adipose (fat storing) tissues and Previous Year’s Questions liver Which of the following is not a (ii) Water Soluble Vitamins fat soluble vitamin? y Vitamins which are soluble in water but insoluble in fat or oils. [AIPMT-2011] y Vitamin B & vitamin C are soluble in water so (1) Vitamin B complex they can grouped together. (2) Vitamin D (3) Vitamin E (4) Vitamin A Q4 Deficiency of which vitamin causes (i) Pernicious anaemia (ii) convulsions Sol. (i) Pernicious anaemia is caused by deficiency of vitamin B (ii) Convulsion sare caused by deficiency of vitamin B.. 12 6 Biomolecules 34. S.No. Name of Vitamins Sources Deficiency diseases Carrots, fish liver oil, Xerophthalmia, night (i) Vitamin A butter and milk blindness Vitamin B1 Milk, green vegetables, Beri beri (loss of appetite, (ii) (Thiamine) cereals and yeast retarded growth) Digestive disorders, cheilosis (fissuring Vitamin B2 Egg white, milk, liver, (iii) at corners of mouth (Riboflavin) kidney and lips) and burning sensation of the skin. Vitamin B6 Milk, cereals, egg yolk (iv) Convulsions (Pyridoxine) and grams, yeast Fish, meat, egg and Pernicious anaemia (RBC (v) Vitamin B12 curd deficient in haemoglobin) Vitamin C Amla, Citrus fruits and (vi) Scurvy (bleeding gums) (Ascorbic acid) green leafy vegetables Osteo- malacia (joint Exposure to sunlight, pain in adults and soft (vii) Vitamin D fish and egg yolk bones) and rickets (bone deformities in children) Vegetable oils like Increased fragility of (viii) Vitamin E sunflower oil ,wheat RBCs and muscular germ oil,etc. weakness Vegetable oils like Increased blood clotting (ix) Vitamin K sunflower oil, etc. time Biomolecules 35.  NUCLEIC ACIDS y For each and every species, every generation Concept Ladder resembles its ancestors in many ways. y For this transmission of inherent characters Nucleic acids play nucleus of a living cell is responsible, which an essential role in is also termed as heredity. transmission of the y Chromosomes are particles made up of hereditary characteristics proteins and another type of biomolecules and in the biosynthesis of called nucleic acids and present in the proteins. nucleus of the cell is responsible for heredity. y Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) are two types of nucleic acids. They are also called polynucleotides as they are long chain polymers of nucleotide. y Nucleic acids contain the elements nitrogen, carbon, oxygen, phosphorus and hydrogen. Chemical Composition of Nucleic Acids y The Complete hydrolysis of DNA (or RNA) Rack your Brain yields a pentose sugar, phosphoric acid and nitrogen containing heterocyclic compounds What are the main function of DNA (called bases). and RNA in organisms? Pentose Sugar y In DNA molecules, the sugar moiety is β-D-2- deoxyribose whereas in RNA molecule, it is β-D-ribose. Previous Year’s Questions Bases Deficiency of vitamin B1 causes y The bases that occur in nucleic acids are the disease derivatives of pyrimidine and purine. [AIPMT-2012] (1) Convulsions (2) Beri-Beri Biomolecules (3) Cheilosis (4) Sterility 36. y Pyrimidine bases are uracil, thymine and cytosine. y The purine bases found in nucleic acids are adenine and guanine. Previous Year’s Questions In DNA, the linkages between y DNA contains 4 bases viz. adenine (A), guanine different nitrogenous bases are (G), cytosine (C) and thymine (T). [NEET-2013] y RNA also contains 4 bases, the first 3 bases (1) Phosphate linkage (adenine (A), guanine (G), cytosine (C)) are (2) H-bonding same as in DNA but the fourth one is uracil (3) Glycosidic linkage Biomolecules (U). (4) Peptide linkage 37.  Chargaff Rule y In 1955 Erwin Chargaff given the Chargaff Rule. Rack your Brain The rule states that ‘For any given species in DNA, the ratio of adenine to thymine is equal What is the chargaff rule and why to the ratio of cytosine to guanine. The ratio it is important? is termed as Chargaff’s ratio. y This rule was important for solving the structure of DNA. y Chargaff’s rule, [A] + [G] = [C] + [T] y DNA from any species of any organism should have a 1:1 stoichiometric ratio of purine and pyrimidine bases. Structure of Nucleic Acids Nucleoside y Nucleoside is a unit formed by the attachment Previous Year’s Questions of a base to 1 position of sugar. Sugar + Base = Nucleoside in DNA, the linkages between y In nucleosides, for distinguish between bases different nitrogenous bases are from it, the sugar carbons are numbered as [NEET-2013] 1, 2, 3 etc. (1) phosphate linkage (2) H-bonding Nucleotide (3) glycosidic linkage y A nucleotide unit formed by the attachment (4) peptide linkage of a base 1 position of sugar and attachment of phosphoric acid with 5 position of sugar. Sugar + Base + Phosphoric acid = Nucleotide y By phosphodiester linkage between 5 and 3 carbon atoms of the pentose sugar, nucleotides are joined together. The formation Biomolecules of a typical dinucleotide. 38. y A simplified version f nucleic acid chain is as shown below. Double strand helix structure for DNA y The sequence of bases along the DNA or RNA chain shows primary structures of these and it controls the specific properties of nucleic acids. y An RNA molecule is usually a single chain of ribose containing nucleotides. y DNA consists of 2 long strands of Previous Year’s Questions polynucleotides coiled around each other in the form of a double helix (Watson and Crick Which of the following is correct model) ladder like structure joint together by about H-bonding in nucleotide? hydrogen bonding. [AIPMT] y Here, hydrogen bonding is in between the (1) A-T, G-C (2) A-G, T-C Biomolecules nitrogenous base molecules of the nucleotide (3) G-T, A-C (4) A-A, T-T monomer. Adenine with thymine forms two 39.  hydrogen bonds while guanine forms three hydrogen bonds with cytosine. Rack your Brain y Thymine combines only with deoxyribose sugar while uracil combines with only ribose What type of linkage holds sugar. together the monomers of DNA? Concept Ladder Mutation is sudden change in base sequence of DNA due to radiations or chemicals. Ribonucleic Acid (RNA) y RNA single stranded helics is present which sometimes foldsback on itself. Previous Year’s Questions y Its molecules are of 3 types and all three of them performs different functions. The central dogma of molecular y They are named as ribosomal RNA (r-RNA), genetics states that the genetic messenger RNA (m-RNA), and transfer RNA information flows from (t-RNA). [NEET-2016] (1) Amino acids → Proteins Central Dogma y Central Dogma was first proposed in 1958 by → DNA Francis Crick, discoverer of the structure of (2) DNA → Carbohydrates → DNA. Proteins y Transcription, Translation and Replication (3) DNA → RNA → Proteins Biomolecules are the 3 main processes used by all cells (4) DNA → RNA → Carbohydrates 40.  for maitaining their genetic information and also for converting the genetic information Definition encoded in DNA into gene products, which are either proteins or RNA, depending on the A sequence of bases on DNA gene. is also unique for a person and information regarding this is called DNA fingerprinting. Difference Between DNA and RNA S.No. Deoxyribonucleic Acid (DNA) Ribonucleic Acid (RNA) DNA occurs n the nucleus of the RNA occurs in the cytoplasm of the (i) cell. cell. The sugar present in DNA is The sugar present in RNA is D-(–)- (ii) D-(–)-2-deoxyribose. ribose. DNA contains cytosine and RNA contains cytosine and uracil as thymine as pyrimidine bases (iii) pyrimidine bases and guanine and and guanine and adenine as adenine as purine bases. purine bases. DNA has double-standard RNA has single standard a-helix (iv) a-helix structure. structure. RNA usually does undergo (v) DNA undergoes replication. replication. DNA controls the transmission RNA controls the synthesis of (vi) of hereditary effects. proteins. DNA Fingerprinting y For cracking the genetic code Dr. Khorana, Marshall Nirenberg and Robert Holley won Biomolecules the Nobel Prize for Medicine and Physiology in 1968. 41.  y DNA fingerprinting cannot be altered by any known treatment and is same for every cell. Concept Ladder y It is now used : (i) For determining paternity of an individual (ii) in forensic laboratories for identification of The process by which criminals. a single DNA molecule (iii)  for identifying racial groups to rewrite produces two identical biological evolution. copies of itself is called (iv) for identifying the dead bodies in any accident cell division (mitosis) or by comparing the DNA’s of parents or children. replication. Biological Functions of Nucleic Acids y During cell division a DNA molecule is capable of self-duplication and identical DNA strands are transferred to daughter cells. y In the cell various RNA molecules can synthesisize proteins but for a particular Previous Year’s Questions protein the message for the synthesis is present in DNA. An example of biopolymer is y DNA is the chemical basis of heredity and can [AIPMT] be considered as the reserve of information (1) teflon (2) neoprene about genetic. (3) nylon-6, 6 (4) DNA y Over millions of years DNA is exclusively responsible to maintain the indentification of different species of organisms. The Major Complex Biomolecules of Cells Biomolecule Building Block Major Functions Protein Amino acid Basic structure and function of cell DNA Deoxyribonucleotide Hereditary information RNA Ribonucleotide Protein synthesis Polysaccharide Monosaccharide Storage form of energy Storage form of energy for meeting Lipids Fatty acids & glycerol Biomolecules long term demands 42. HORMONES y They are the molecules that act as intercellular Definition messengers. y Hormones are substances or biomolecules Hormones are produced by manufactured in minute amounts in endocrine endocrine glands in the body or ductless glands. and are poured directly in the y They are carried directly into different parts blood stream which transports by the blood stream. them to the site of action. y The major hormone secreting glands include the intestinal mucosa pancreas, adrenals, thyroid, pituitary, ovaries and testes. Types of Hormones (1) Steroids y These type of hormones are produced by Concept Ladder adrenal cortex and gonads (testes in males and ovaries in females). If adrenal cortex does Ex : estrogens and androgens. not function properly y For various functions of the body hormones then one of the results released by the adrenal cortex play very may be Addison’s important role. disease characterised by hypoglycemia, (i) Glucocorticoids weakness and increased y They control the modulate inflammatory susceptibility to stress. reactions, carbohydrate metabolism and are involved in reactions to stress. (ii) Mineralocorticoids y They control the level of excretion of salt and water by the kidney. Previous Year’s Questions (2) Polypeptids — e.g. insuline and endorphins. Which of the following hormones is produced under the conditions (3) Amino Acids Derivatives — epinephrine and of stress which stimulate norepinephrine. glycogenolysis in the liver of human beings? [NEET-2014] (1) Thyroxin (2) Insulin Biomolecules (3) Adrenaline (4) Estradiol 43.  Functions of Hormones y Hormones have several functions in the body. Rack your Brain y In the body they help for maintaining the balance of biological activities. Which disease is caused by y The example of this function like insulin deficiency of insulin? keeps the blood glucose level within the narrow limit. When there is rapid rise in blood glucose level in response insulin is released. y Hormone glucagon tends to increase the glucose level in the blood. Insulin and Glucagon hormones will regulate the glucose level in the blood. y Growth and sex hormones play role in development and growth. y Thyroxine formed in thyroid gland is an iodinated derivative of amino acid tyrosine. y Lethargyness and obesity are the Previous Year’s Questions characteristics of hypothyroidism which is due to abnormally low level of thyroxine. Which of the following y Hyperthyroidism is caused due to increased statements is not correct? level of thyroxine. [NEET-2017] y Hypothyroidism and enlargement of the (1)  Ovalbumin is a simple food thyroid gland are caused by low level of reserve in egg-white iodine in the diet.By adding sodium iodide to (2) Blood proteins thrombin and commercial table salt (“Iodised” salt), it can fibrinogen are involved in be controlled. blood clotting. y Hormones released by gonads are responsible (3) Denaturation makes the for developing secondary sex characters. proteins more active. y Testosterone is responsible for developing (4) Insulin maintains sugar level secondary male characteristics (facial hair, in the blood of a human body.