Chapter 31 Biomolecules PDF

60 1428 Biomolecules Chapter E3 31 Biomolecules 3 Aldotriose Ketotriose 4 Aldotetrose Ketotetrose 5 Aldopentose Ketopentose 6 Aldohexose Ketohexose 7 Aldoheptose Ketoheptose U ID All living bodies are composed of several lifeless substances which are present in their cells in a very complex but high...

60 1428 Biomolecules Chapter E3 31 Biomolecules 3 Aldotriose Ketotriose 4 Aldotetrose Ketotetrose 5 Aldopentose Ketopentose 6 Aldohexose Ketohexose 7 Aldoheptose Ketoheptose U ID All living bodies are composed of several lifeless substances which are present in their cells in a very complex but highly organised form. These are called biomolecules. Some common examples are carbohydrates, proteins, enzymes, nucleic acids, lipids, amino acids, fats etc : Carbohydrates D YG Living organisms Organs Tissues Cells Organelles Biomolecules. The carbohydrates are naturally occurring organic substances. They are present in both plants and animals. U "Carbohydrates are defined as a class of compounds that include polyhydric aldehydes or polyhydric ketones and large polymeric compounds that can be broken down (hydrolysed) into polyhydric aldehydes or ketones.” ST Carbohydrates contain  C  O and OH groups. A carbonyl compound reacts with an alcohol to form hemiacetal. The name of simpler carbohydrates end is –ose. Carbohydrate with an aldehydic structure are known as aldoses and those with ketonic structure as ketoses. The number of carbon atom in the molecule is indicated These are the simplest one unit non-hydrolysable sugars. They have the general formula Cn H 2n On where n varies from 3 to 9 carbon atoms. About 20 monosaccharides occur in nature. The simplest are trioses (n=3) C 3 H 6 O3 Triose H CO | ; H  C  OH ; | CH 2 OH CH 2 OH | C O | CH 2 OH Gly ceraldehy de Dihy droxy acetone The most important naturally occurring monosaccharides are pentoses and hexoses. A common pentose is ribose and two common hexoses are glucose and fructose. Except ketotriose {dihydroxyacetone}, all aldose and ketoses {monosaccharides} contain asymmetric carbon atoms and are optically active. by Greek prefix. Glucose; (C6H12O6) or Aldo-hexose Table : 31.1 Number of carbon atoms in the molecule Monosaccharides Aldose Ketose Glucose is known as dextrose because it occurs in nature as the optically active dextrorotatory isomer. It Biomolecules 1429 is also called grape sugar as it is found in most sweet (c) Reaction with metallic hydroxides fruits especially grapes. C 6 H 11 O 5 — OH  H O — Ca — OH  Calcium hydroxide Glucose (1) Preparation : C 6 H 11 O 5 — O — Ca — OH  H 2 O Calcium glucosate (i) Laboratory method  Glucose behaves as a weak acid. Instead of Ca(OH )2 we can take other metallic hydroxide like  H C12 H 22 O11  H 2 O   C 6 H 12 O6  C 6 H 12 O6 Glucose Fructose Ba(OH )2 , Sr (OH )2 , Cu(OH )2 etc to form glucosate which is HCl (dil.) is used for hydrolysis. Glucose being much less soluble in alcohol than fructose separates out HCl C6 H 11 O5 — OH  H OCH 3   C6 H 11 O5 OCH 3  H 2 O (ii) Manufacture : It is obtained on a large scale by the hydrolysis of starch (corn starch or potato starch) with dilute sulphuric acid or hydrochloric acid.  H (C 6 H 10 O 5 )n  nH 2 O   nC 6 H 12 O 6 320 C , 2  3 atm Glucose OCH3 CH3O H C C | | (CHOH) (CHOH)3 O O | | 3 CH CH | | H CH2OH CH2O -Methyl -Methyl H glucoside glucosideof ring structure This reaction shows the presence in glucose. (ii) Reactions of carbonyl group (Aldehydic group) (a) Reduction Na  Hg CH 2 OH (CHOH ) 4 CHO  2 H   ID A thin paste of starch is boiled with dilute acid till the hydrolysis is complete. The excess of acid is neutralised with chalk (calcium carbonate) and the filtrate containing glucose is decolourised with animal charcoal. The solution is concentrated and evaporated under reduced pressure. Glucose is obtained in crystalline form. (2) Physical properties : It is a colourless α- and β-Methyl glucoside H E3 by crystallising on cooling. Starch soluble in water. (d) Formation of glycosides 60 Cane sugar (Sucrose) U crystalline solid, melts at 146 o C. It is readily soluble in water. From aqueous solution, it separates as a crystalline monohydrate (C6 H 12 O6.H 2 O) which melts at o ST U D YG 86 C. It is sparingly soluble in alcohol but insoluble in ether. It is less sweet (three-fourth) than cane sugar. It is optically active and the ordinary naturally occuring form is (+) glucose or dextro form. It shows mutarotation. (3) Chemical properties (i) Alcoholic reactions (Reactions due to –OH group) : (a) Reaction with acid chlorides and acid anhydride CHO CHO | | ZnCl 2  (CHOOCCH 3 )4  5 HCl (CHOH )4  5 CH 3 COCl  Acety lchloride | | CH 2 OH CH 2 OOCCH 3 Glucose Penta -chloroglucose (Glucose penta -chloride) H 2O CH 2 OH (CHOH )4 CH 2 OH Sorbitol On prolonged heating with concentrated HI and red phosphorus at 110 o C , glucose forms a mixture of 2iodohexane and n-hexane. (b) Oxidation  Reaction with Fehling solution CH 2 OH (CHOH )4 CHO  2CuO  Glucose CH 2 OH (CHOH )4 COOH Cu 2 O. Gluconic acid (red ppt.)  Reaction with Tollen’s reagent CH 2 OH (CHOH )4 CHO  Ag 2 O  CH 2 OH (CHOH )4 COOH  2 Ag. (Mirror) [or black ppt.]  Reaction with Bromine water Br2 / H 2 O CH 2 OH (CHOH )4 CHO  [O]    Glucose CH 2 OH (CHOH )4 COOH. Glucose penta -acetate This shows that a molecule of glucose contains 5 – OH groups. (b) Reaction with PCl5 CHO CHO | | (CHOH )4  5 PCl 5  (CHCl )4  5 POCl 3  5 HCl | | CH 2 OH CH 2 Cl Glucose Glucose Gluconic acid  Reaction with Nitric acid HNO 3 CH 2 OH (CHOH )4 CHO  3[O]    Glucose (C6 ) COOH (CHOH )4 COOH  H 2 O. Saccharic acid (C6 ) (c) Reaction with HCN CH 2 OH (CHOH )4 CHO  HCN  CN CH 2 OH (CHOH )4 CH Glucose cy anohy drin OH 1430 Biomolecules Glucose oxime H C | HO – C – | H HO – C – | H H – C – OH | H – C – OH | CH2OH C | H – C – OH | HO – C – | H H – C – OH | H – C – OH | CH2OH D(+) Glucose D(+) Mannose Epimers (d) Action of concentrated hydrochloric acid Conc. HCl C 6 H 12 O6    CH 3 COCH 2 CH 2 COOH  HCOOH  H 2 O Laevulic acid On treatment with conc. HCl, glucose can also form hydroxymethyl furfural. CH — CH + 3H2O C6H12O || || 6 C — CHO HOCH2 — C U ID (e) Reaction with Phenyl hydrazine (Fischer's mechanism) : When warmed with excess of phenyl hydrazine, glucose first forms phenylhydrazone by condensation with – CHO group. CHO +H2NNHC6H5 CH =NNHC6H5 | | O Phenyl CHOH CHOH hydrazine | | Warm (CHOH) (CHOH) | 3 | 3 CH2O CH2OH H Glucos Glucose phenyl hydrazone e The adjacent – CHOH group is then oxidised by a second molecule of phenyl hydrazine. CH = CH=NNHC6H | | NNHC6H5 5 C=O + C6H5NH2 + CHOH +H2NNHC6H5 | | NH3 (CHOH) (CHOH)3 | | 3 CH2OH CH2O Keto compound of H Glucose phenyl hydrazone The resulting carbonyl compounds reacts with a third molecule of phenyl hydrazine to yield glucosazone. O O H 60 CH 2 OH (CHOH )4 CH  NOH  H 2 O. E3 (d) Reaction with hydroxyl amine CH 2 OH(CHOH )4 CHO  NH 2 OH + C6 H 12 O6   2C 2 H 5 OH  2CO 2 Zymase Glucose Ethanol ST U (b) Dehydration : When heated strongly or when treated with warm concentrated sulphuric acid, glucose is dehydrated to give a black mass (sugar carbon). (c) Reaction with alkalies : When warmed with concentrated alkali, glucose first turns yellow; then brown and finally gives a resinous mass. A dilute solution of glucose, when warmed with dilute solution of alkali, some glucose is converted into fructose and mannose. D-glucose and D-mannose are epimers. CH = O | H — C — OH CH2OH | C=O Glucose  HO — CH || HO — C Eno l Eno l Fructos CH = e O | HO — C — H     CH — OH || C — OH Manno se furfural This on acid treatment gives laevulic acid D YG CH =NNHC6H5 CH = | | NNHC6H5 C = O +H2NNHC6H C= NNHC6H5 | | 5 H2O (CHOH) (CHOH) | 3 | 3 CH2O CH2OH H Glucosazo (iii) Miscellaneous reactions ne (a) Fermentation O Hydroxymethyl (4) Uses (i) In the preservation of fruits and preparation of jams and jellies. (ii) In the preparation of confectionary and as a sweetening agent. (iii) As a food for patients, invalids and children. (iv) In the form of calcium glucosate as medicine in treatment of calcium deficiency. (v) As a reducing agent in silvering of mirrors. (vi) As a raw material for alcoholic preparations. (vii) In industrial preparation of vitamin-C. (viii) In the processing of tobacco. (ix) As an intravenous injection to the patients with lower glucose content in blood. (5) Test of glucose (i) When heated in a dry test tube, it melts, turns brown and finally black, giving a characteristic smell of burnt sugar. (ii) When warmed with a little conc. H 2 SO 4 , it leaves a charred residue of carbon. (iii) When it is boiled with dilute NaOH solution, it first turns yellow and then brown. Biomolecules 1431 (iv) Molisch’s test : This is a general test for carbohydrates. Two or three drops of alcoholic solution of -naphthol is added to 2mL of glucose solution. 1 mL of concentrated H 2 SO 4 is added carefully along the -D-Glucose sides of the test tube. The formation of a violet ring, at the junction of two liquids confirms the presence of a carbohydrate. 60 (v) Silver mirror test : A mixture of glucose and ammonical silver nitrate is warmed in a test tube. Appearance of silver mirror on the inner walls confirms glucose. (c) Fischer and Tollen’s proposed that the ring or (vi) Fehling’s solution test : A little glucose is warmed with Fehling’s solution. A red precipitate of cuprous oxide is formed. the internal hemiacetal is formed between C 1 and C 4. It means the ring is Furan type or 5-membered ring; (vii) Osazone formation : Glucose on heating with excess of phenyl hydrazine in acetic acid gives a However according to Haworth and Hirst the ring E3 this is called Furanose strucutre, is formed between C 1 and C 5. It means the ring is Pyran type or 6-membered ring, this is called yellow crystalline compound, m.pt. 205 o C. (6) Structure of glucose Pyranose structure. CH2 ID (i) Open chain structure : The structure of Dglucose as elucidated by Emil Fischer is, H O 1 C |2 H – C – | OH– 3C – HO |4 H H – C – OH |5 H – C – OH |6 CH2OH 4 3 5 4 3 D YG U CH — CH HC ||5 || 2 ||2 || CH6 CH HC CH 1 CH 1 O O Pyra Fura n n (d) Haworth structure : The two forms of Dglucose are also shown by Haworth projection formula which are given below, 6CH2OH 5 D-Glucose (Specific rotation = 52.5°) (b) Ordinary glucose is -glucose, with a fresh aqueous solution has specific rotation, [ ]D  111 o. On U keeping the solution for some time; -glucose slowly changes into an equilibrium mixture of -glucose (36%) and -glucose (64%) and the mixture has specific rotation + 52.5o. Similarly a fresh aqueous solution of -glucose specific rotation, ST having [ ] D  19. 7 o , on keeping (standing) gradually changes into the same equilibrium mixutre (having, specific rotation  52.7 o ). So an aqueous solution of glucose shows a physical property, known as mutarotation, i.e., a change in the value of specific rotation (muta=change; rotation = specific rotation) is called mutarotation. H O C1 |2 CHOH |3 CHOH |4 CHOH |5 CHOH |6 CH2O H DGlucose []D = + 52.5o H OH1 C |2 CHOH |3 CHOH |4 CHOH |5 CH O |6 CH2OH []D = + 111o HO H |1 C |2 CHOH |3 CHOH |4 CHOH |5 O CH | CH O 6 2 -DH Glucose []D = + 19.7o H 4 OH O H OH H 3 2 H -D 6CH2OH 5 H H 4 1 OH O H O H OH 1 OH H 3 2 H OH -D OH H glucose glucose Fructose, fruit sugar (C6H12O6) or ketohexose It is present in abundance in fruits and hence is called fruit sugar. It is also present in cane sugar and honey alongwith glucose in combined form. The polysaccharide inulin is a polymer of fructose an gives only fructose on hydrolysis. Since naturally occurring fructose is laevorotatory, it is also known as laevulose. (1) Preparation : (i) Hydrolysis of cane sugar H 2 SO 4 (dil.) C12 H 22 O11  H 2 O   C 6 H 12 O6  C 6 H 12 O6 Cane sugar Warm D-Glucose D-Fructose 1432 Biomolecules is known as inversion.  The excess of sulphuric acid is neutralised by adding milk of lime. A little more of lime is added which converts both glucose and fructose into calcium glucosate and calcium fructose respectively. C 6 H 11 O 5  O  CaOH  CO 2  C 6 H 12 O 6  CaCO 3 Calcium fructose Optical activity of natural form Dextrorotato ry Laevorotatory With ethyl alcohol Almost insoluble More soluble Gluconic acid No reaction Saccharic acid (Glucaric acid) Mixture of glycollic acid, tartaric acid and trihydroxy glutaric acid Sorbitol Mixture of sorbitol and mannitol Oxidation (a) With bromine water (b) With nitric acid Fructose (ii) Hydrolysis of Inulin with dilute sulphuric acid Reduction H 2 SO 4 (dil.) (C 6 H 10 O 5 )n  nH 2 O   nC 6 H 12 O 6 Inulin (2) Properties : The anhydrous fructose is a E3 Fructose Calcium hydroxide Forms calcium glucosate, soluble in water Forms calcium fructosate, insoluble in water Molisch’s reagent Forms a violet ring Forms a violet ring Fehling’s solution Gives red precipitate Gives precipitate Tollen’s reagent Forms silver mirror Forms silver mirror Phenyl hydrazine Forms osazone Forms osazone Resorcinol + HCl (dil.) (Selivanoff’s test) No colouration Gives red or brown colour or precipitate Freshly prepared ammonium molybdate sol. + few drops of acetic acid (Pinoff’s test). Light blue colour Bluish green colour on heating Alcoholic -naphthol + HCl (conc.) (Furfural test) No colouration A purple colour (violet) on boiling o colourless crystalline compounds. It melts at 102 C. It is soluble in water but insoluble in benzene and ether. HOH2C []D = – 92° C | HO – C – | H H – C – | OH H – C – | OH CH2 U o r CH2O | H C=O | (CHOH) | 3 CH2O H OH O D YG CH2O | H C= O | HO – C – | H H – C – OH | H – C – OH | CH2O D-Fructose H ID It is less soluble in water than glucose. It is the sweetest of all sugars and its solution is laevorotatory. Like glucose, it also shows mutarotation. - D- Fructose []D = – 21o CH2OH OH O - D- Fructose []D = – 133o aldehydic group. Table : 31.2 Comparison between glucose and fructose Property Glucose red  Fructose gives reactions similar to glucose. The difference in properties is due to the fact that it contains a ketonic group while glucose contains an ST U C | HO – C – | HH – C – | OH – C – H | OH CH 2 60 The solution having equal molecules of D-glucose and D-fructose is termed invert sugar and the process Fructose Molecular formula C6H12O6 C6H12O6 Nature Polyhydroxy aldehyde. Polyhydroxy ketone Melting point 146oC 102oC Interconversions : (1) Chain Lengthening of Aldoses (KillianiFischer synthesis) : The conversion of an aldose to the next higher member involves the following steps : (i) Formation of a cyanohydrin. (ii) Hydrolysis of – CN to – COOH forming aldonic acid. Biomolecules 1433 (iii) Conversion of aldonic acid into lactone by heating. (iv) The lactone is finally reduced with sodium amalgam or sodium borohydride to give the higher aldose. Arabinose (Aldopento se) O=C | CHOH | CHOH heat | CH – | H2O CHO | H (4) Conversion of a ketose to the isomeric aldose COOH | H2O/H CHOH + | Ba(OH (CHOH) )2 | 3 CH2O Gluconic H acid CH2O | H C=O | H2/ (CHOH) Ni | 3 CH2O H Fructo O=C–H | O CHO Na – Hg | H in acid solution (CHOH) | 3 CH2OH se The disaccharides yield on hydrolysis two monosaccharides. Those disaccharides which yield two hexoses on hydrolysis have a general formula C12 H 22 O11. The hexoses obtained on hydrolysis may be Glucose CH2OH Lactone (Aldohexos e) same or different. COOH | CHOH | (CHOH) | 3 CH2OH Aldohexose (DGlucose) Ca- salt H2O2+Fe3+ CHO | (CHOH) | 3 CH2O Aldopentos H D YG Br2 H2O Aldonic acid e (ii) By Wohl’s method (D- Arabinose) CH = NOH | CHOH | (CH3CO)2O | (CHOH) CH2O 3 H Oxim U O = CH | CHOH | (CHOH) H2NO | H 3 CH2O Glucose H (Aldohexose) e ST CN CN CHO | | | CHO.COCH3 AgO CHO H – | | | war H HCN (CHOH) CH2O | | 3 (CHO.COCH3)3 m Aldopento H (CHOH) CH2O.COCH CH2OH 3 se 3 (3) Conversion of an aldose to the isomeric Ketose Three steps are involved, O = CH HC=NNHC6H | | 5 C=NNHC6H CHOH 2H2O/H+ C6H5NHNH | | 5 (CHOH) (CHOH) (Excess) (– 2 | | 3 3 2C6H5NHNH2) CH2OH CH2O Glucos H e Osazon HC=O e | C=O 2H | Zn/CH 3COOH (CHOH) | 3 CH2OH Oson e H 2O C12 H 22 O11   C 6 H 12 O 6  C 6 H 12 O 6  CH2OH | C=O | (CHOH) | 3 CH2OH Fructo se H Sucrose Glucose Fructose Lactose  Glucose + Galactose  H 2O H Maltose  Glucose + Glucose  U (2) Chain Shortening of aldoses (i) An aldose can be converted to the next lower member by Ruff Degradation. It involves two steps. CHO | CHOH | (CHOH) | 3 CH2OH Glucos e E3 Disaccharides CHO | CHOH | (CHOH) + | 3 CH2OH CH2O | H CHOH [O | (CHOH) H2O]2 | Fe2+ 3 CH2OH 60 HCN CN | CHOH | (CHOH) | CH23OH ID CHO | (CHOH) | 3 CH2OH H 2O H The hydrolysis is done by dilute acids or enzymes. The enzymes which bring hydrolysis of sucrose, lactose and maltose are invertase, lactase and maltase, respectively. Out of the three disaccharides, sucrose (cane-sugar) is the most important as it is an essential constituent of our diet. In disaccharides, the two monosaccharides are joined together by glycoside linkage. A glycoside bond is formed when hydroxy group of the hemiacetal carbon of one monosaccharide condenses with a hydroxy group of another monosaccharide giving – O– bond. (1) Sucrose; Cane-sugar [C12H22O11] : It is our common table sugar. It is obtained from sugar cane and sugarbeets. It is actually found in all photosynthetic plants. (i) Properties : It is a colourless, odourless, crystalline compound. It melts at 185 – 186oC. It is very soluble in water, slightly soluble in alcohol and insoluble in ether. It is dextrorotatory but does not show mutarotation. It is a non-reducing sugar as it does not reduce Tollen’s Glycoside CH2OH 6 5 4 linkage O 1 OH OH 2 3 OH O 6 CH2OH O 2 5 OH 4 3 OH Structure of CH2OH 1 1434 Biomolecules  H C 12 H 22 O11  H 2 O   Sucrose C 6 H 12 O 6  C 6 H 12 O 6 D- Glucose D- Fructose (This mixture is laevorotat ory) Sucrose solution is dextrorotatory. Its specific  52 and of D-fructose is  92. Therefore, the net specific rotation of an equimolar mixture of D-glucose and D-fructose is. D YG o Gives yellow precipitate of glucosazon e No effect, i.e., does not form osazone Aqueous resorcinol + conc. HCl solution No effect Reddish-brown precipitate which dissolves in ethanol. 60 On heating with phenyl hydrazine Polysaccharide (Starch and cellulose) Polysaccharides are polymer of monosaccharide. The most important polysaccharides are starch and cellulose. They have a general formula (C6 H10 O5 )n. Starch (Amylum) is most widely distributed in vegetable kingdom. It is found in the leaves, stems, fruits, roots and seeds. Concentrated form of starch is present in wheat, corn, barley, rice, potatoes, nuts, etc. It is the most important food source of carbohydrates. (1) Starch and its derivatives : Starch is a white amorphous substance with no taste or smell. When U rotation is  66.5 o. But on hydrolysis, it becomes laevorotatory. The specific rotation of D-glucose is o precipitate of Cu2O ID (ii) Uses (a) As a sweetening agent for various food preparations, jams, syrups sweets, etc. (b) In the manufacture of sucrose octa-acetate required to denature alcohol, to make paper transparent and to make anhydrous adhesives. (2) Inversion of cane-sugar : The hydrolysis of sucrose by boiling with a mineral acid or by enzyme invertase, produces a mixture of equal molecules of Dglucose and D-fructose. solution E3 or Fehling’s reagent. Sucrose, on heating slowly and carefully, melts and then if allowed to cool, it solidifies to pale yellow glassy mass called ‘Barley sugar’. When heated to 200oC, it loses water to form brown amorphous mass called Caramel. On strong heating, it chars to almost pure carbon giving smell of burnt sugar. It is composed of -D-glucopyranose unit and a -D-fructofuranose unit. These units are joined by -glycosidic linkage between C –1 of the glucose unit and C – 2 of the fructose unit.  52 o  92 o  20 o 2 heated to a temperature between U ST Table : 31.3 Distinction between glucose and sucrose Test Glucose Sucrose With conc. H2SO4 in cold No effect Charring occurs and turns black Molisch’s reagent Violet ring is formed Violet ring is formed With NaOH Turns yellow No effect With Tollen’s Solution Gives silver mirror No effect With Fehling’s Gives red No effect it changes into dextrin. At higher temperature charring occurs. When boiled with dilute acid, starch ultimately yields glucose. (C 6 H 10 O 5 )n  (C 6 H 10 O 5 )n1  Starch Thus, in the process of hydrolysis of sucrose, the specific rotation changes from  66.5 to  20  , i.e., from dextro it becomes laevo and it is said that inversion has taken place. The process of hydrolysis of sucrose is thus termed as inversion of sugar and the hydrolysed mixture having equal molar quantities of Dglucose and D-fructose is called invert sugar. The enzyme that brings the inversion is named as invertase. 200  250 o C, Dextrin C 12 H 22 O11  C 6 H 12 O 6 Maltose Glucose Both n and n1 , are unknown, but n is believed to be greater than n1. When treated with enzyme, diastase, it yields maltose. 2(C 6 H 10 O 5 )n  nH 2 O  nC 12 H 22 O11 Maltose Starch solution gives a blue colour with a drop of iodine which disappears on heating to 75  80 o C and reappears on cooling. The exact chemical nature of starch varies from source to source. Even the starch obtained from same source consists of two fractions (i) amylose and (ii) amylopectin. Amylose is a linear polymer while amylopectin is a highly branched polymer. Both are composed of -Dglucose units linked by glycosidic linkages. The number of D-glucose units in amylose range from 60 – 300. It is Biomolecules soluble in hot water, Amylopectin consists of D-glucose units from 300 – 600. It is insoluble in water. O O OH OH O O OH CH2OH O OH (C 6 H 10 O 5 )n  nH 2 O  nC 6 H 12 O 6 Cellulose OH n Repeating monomer Structure of amylose CH2O H O OH O OH OH n Repeating -1, monomer bonds H CH2 O OH CH2O O O OH OH H O bonds of Structure amylopectin O OH O -1, 4-Glycoside H O OH Repeating monomer The cattle, goats and other ruminants can feed directly cellulose (grass, straw, etc.) as they have digestive enzymes (celluloses) capable of hydrolysing cellulose into glucose. Man and many other mammals lack the necessary enzymes in their digestive tract and thus cannot use cellulose as food stuff. H H O O OH H H H OH U Uses : Starch and its derivatives are used Glucose Cellulose is a straight chain polysaccharide composed of D-glucose units which are joined by Bglycosidic linkages between C-1 of one glucose unit and C-4 of the next glucose unit. The number of D-glucose H OH to 50000. units in cellulose 300 CH2OH CH2OH ranges from 6-GlyosideO CH2O O O ID O into D-glucose. OH OH -1, 4-Glycoside bonds cold, it slowly passes into solution. The solution when diluted with water, a starch like substance amyloid is precipitated and is called parchment paper. When boiled with dilute H 2 SO 4 , it is completely hydrolysed 60 O O CH2OH CH2OH When it is treated with concentrated H 2 SO 4 in E3 CH2OH 1435 (i) As the most valuable constituent of food as rice, bread, potato and corn-flour, etc. D YG (ii) In the manufacture of glucose, dextrin and adhesives (starch paste). (iii) In paper and textile industry. (iv) In calico printing as a thickening agent for colours. (v) Nitro starch is used as an explosive. (vi) Starch-acetate is a transparent gelatin like mass and is used mainly for making sweets. ST U (2) Cellulose : It is found in all plants and so is the most abundant of all carbohydrates. It is the material used to form cell walls and other structural features of the plants. Wood is about 50% cellulose and the rest is lignin. Cotton and paper are largely composed of cellulose. Pure cellulose is obtained by successively treating cotton, wool, flax or paper with dilute alkali, dilute HCl or HF. This treatment removes mineral matter, water, alcohol and ether. Cellulose is left behind as a white amorphous powder. Cellulose is insoluble in water and in most of the organic solvents. It decomposes on heating but does not melt. It dissolves in ammonical copper hydroxide solution (Schwitzer’s reagent). Cellulose also dissolves in a solution of zinc chloride in hydrochloric acid. OH O H H H H H H O OH O CH2OH Structure of celluose H O H OH Uses : Cellulose is used (i) As such in the manufacture of cloth (cotton), canvas and gunny bags (jute) and paper (wood, bamboo, straw, etc.) (ii) In the form of cellulose nitrates for the manufacture of explosives (gun-powder), medicines, paints and lacquers. The cellulose nitrates with camphor yield celluloid which is used in the manufacture of toys, decorative articles and photographic films. (iii) In the form of cellulose acetate for the manufacture of rayon (artificial silk) and plastics. Table : 31.4 Distinction between glucose, sucrose, starch Test With iodine solution With Fehling’s solution With Tollen’s reagent With phenyl hydrazine Solubility in water Taste Glucose No effect Gives red precipitate Gives silver mirror Forms yellow osazone Soluble Sweet Sucrose No effect No effect No effect No effect Soluble Sweet Starch Blue colour No effect No effect No effect Insolub le No taste 1436 Biomolecules Amino acids NH Phenyl alanineC:6H5CH2C H (Essenti al) H2 CH C H2 Proline :C 2 Pro / P N H Amino acids with polar but neutral side chain : Name / Structure H | N Tryptophan : Three letter symbol / One letter code NH Glycine CH : 2 Gly / G 2 ST U COOH NH Alanine :CH3CH 2 COOH NH 2 Valine :(CH3)2CH– CH COOH (Essenti NH al) Leucine :(CH3)2CH– 2 CH2CH (Essenti COOH Val / V Leu / L 2 Serine :HO–CH2– CH 2 C2H5–CH– CH | COOH CH3 (Essenti al) 2 Ser / S COOH NH Threonine :CH3CHOH– CH(Essenti al) Tyrosine : HO Cysteine :HS–CH2– CH Thr / T 2 COOH NH2 | CH2–CH– COOH NH Tyr / Y Cys / C 2 COOH NH CH ·S·CH ·CH ·C 2 3 2 2 Methionine : H COOH (Essenti H2 al) NH N 2 Aspargine : C·CH2·C H O COOH H2 N : C·CH2·CH2·C Glutamine H O Met / M Asn / N NH Gln / Q 2 COOH Amino acids with acidic side chains : NH Aspartic acidHOOC·CH : 2·CH NH al) Isoleucine : Ala / A Trp / W C –CH2–CH– COOH (Essenti al) NH U D YG Amino acids with non polar side chain : NH CH ID (R may be alkyl, aryl or any other group) The proteins differ in the nature of R-group bonded to -carbon atom. The nature of R-group determines the properties of proteins. There are about 20 amino acids which make up the bio-proteins. Out of these 10 amino acids (non-essential) are synthesised by our bodies and rest are essential in the diet (essential amino acids) and supplied to our bodies by food which we take because they cannot be synthesised in the body. The amino acids are classified into the following four types and tasulabed as under, Table : 31.5 Name / Structure Three letter symbol / One letter code E3 Amine NH2  group atom COOH CHCOOH | -Carbon Phe / F 2 60 Proteins are a class of biologically important compounds. They are crucial to virtually all processes in living systems. Some of them are hormones which serve as chemical messengers that coordinate certain biochemical activities. Some proteins serve to transport the substances through the organism. Proteins are also found in toxins (poisonous materials) as well as in antibiotics. All the proteins are made up of many amino acid units linked together into a long chain. An amino H Carboxylthat contains acid is a bifunctional organic molecule | both a carboxyl group, –COOH, group as well as an amine group, –NH2. R – C – COOH Asp / D 2 COOH Ile / I NH Glutamic acidHOOC·CH : 2·CH2C H 2 COOH Glu / E Biomolecules (iii) Amino acids with basic side chains : CH 3 COCOOH  CH 3 C  COOH  or Na / C 2 H 5 OH Py ruvic acid || NH COOH 2 C·NH.(CH2)3C H (Essenti (iv) Streker synthesis COOH N H CH Alanine H H H | | | NH 3 HCN R  C  O  R  C  OH  R  C  NH 2 Aldehy de | | CN CN 2 C — CH2 — CH N Arg / R COOH NH al) HC Histidine : CH 3  C H  COOH | NH 2 NH 60 H2 N Lys / K 2 (Essenti al) His / H Cy anohy drin H | R  C  NH 2 | COOH (Essential) (1) Methods of preparation of -amino acids (i) Amination of -halo acids  - Amino propionic acid (Alanine) Lab preparation of glycine H+ Amm.salt of glycine (v) From natural protein : Natural proteins are hydrolysed with dil. HCl or H 2 SO 4 at 250°C in an autoclave when a mixture of -amino acids is obtained. This mixture is esterified and the various esters are separated by fractional distillation. The esters are then hydrolysed into respective -amino acids. U 50 C Cl.CH 2 COOH  3 NH 3    H 2 N.CH 2 COONH 4  NH 4 Cl liquid H2O ID  - Bromo propionic acid Amino nitrile  - Am ino acid CH 3 CH COOH  2 NH 3 CH 3 CH COOH  NH 4 Cl | | Br NH 2  - Chloro acetic acid synthesis H 2 / Pd E3 N H : Arginine Knoop NH 3 NH Lysine :H2N(CH2)4C H 1437 D YG The ammonium salt so obtained is boiled with copper carbonate and cooled when blue colour needles of copper salt of glycine are obtained. Boiled 2[H 2 N  CH 2 COONH 4 ]  CuCO 3    (H 2 NCH 2COO )2 Cu  (NH 4 )2 CO 3 Copper salt of gly cine (2) Physical properties (i) Amino acids are colourless, crystalline substances having sweet taste. They melt with decomposition at higher temperature (more than 200°C). They are soluble in water but insoluble in organic solvents. It is now dissolved in water and H 2 S is passed (ii) Except glycine, all the -amino acids are till whole of the copper precipitates as copper sulphide leaving glycine as the aqueous solution. optically active and have an asymmetric carbon atom (-carbon atom). Hence, each of these amino acids can exist in two optical isomers. In proteins, however, only (H 2 N  CH 2 COO )2 Cu  H 2 S 2 H 2 NCH 2 COOH  CuS  Black ppt. U Gly cine (ii) Gabriel pthalimide synthesis (iii) Zwitter ion and isoelectric point : Since the  NH 2 group is basic and – COOH group is acidic, in CO ST NK + ClCH2COOC2H5 Chloro ethyl acetate CO Pot. CO phthalimide NCH2COOC2H5 CO COOH COOH Phthalic acid 2H2 O HCl one isomer of each is commonly involved. – KCl neutral solution it exists in an internal ionic form called a Zwitter ion where the proton of –COOH group is transferred to the  NH 2 group to form inner salt, also known as dipolar ion. R | In water H 2 N  CHCOOH    + CH2NH2COOH + C2H5OH Glycine  - Amino acid R R | |     H 2 N  CH  COO  H H 3 N  CH  COO  Zwitter ion (Dipolar ion) 1438 Biomolecules The Zwitter ion is dipolar, charged but overall electrically neutral and contains both a positive and negative charge.    -Buty rolactam  - Amino buty ric acid   (3) Chemical properties : Amino acids are amphoteric in nature. Depending on the pH of the solution, the amino acid can donate or accept proton. O H R  C H  C  OH || R  C H  C  OH NH 2 N H3 (Neutral not isolated) pH  0 (Cation in fairly acidic medium) O || R  C H  C O O These lactams have stable five or six membered rings. R  C H  C O |  | NH N H3 U D YG R  CH ST Decarboxylati Ba(OH) onn2,  LiAlH4 4H COOH AminoNHCH alcohol 3 COOH N-Methyl derivative NHCOCH3 Acetylation CH3COCl heat C H 2  C H  COOH   CH 2  CH  COOH ( NH 3 ) | | Acry licacid ( ,  - Unsaturate d acid) NH 2 H  - Amino propionic acid heat CH 3  CH  C H  COOH   CH 3 CH  CHCOOH ( NH 3 ) | | Crotonic acid NH 2 H  - Amino buty ric acid (c) For  and  amino acids RCH COOH HNO2 N-Acetyl derivative RCHOHCOOH -Hydroxy acid – + HCl NH3Cl RCH || (b) For -amino acids RCH -Amino acid CH  R  2 H 2 O O CH- Alkylation CH3Br || Cy clic amide (lactam) NH2 2OH O NH  C C  NH H2N CH2 R – CH Amine NH2 RCH ester R – | R  CH  R  U R  CH AgOH R H2NCH – COOC2H5 Ethyl ID When an ionised form of amino acid is placed in an electric field, it will migrate towards the opposite electrode. Depending on the pH of the medium, following three things may happen  In acidic solution (low pH), the positive ion moves towards cathode.  In basic solution (high pH), the negative ion moves towards anode.  The Zwitter ion does not move towards any of the electrodes. The intermediate pH at which the amino acid shows no tendency to migrate towards any of the electrodes and exists the equilibrium when placed in an electric field is known as isoelectric point. This is characteristic of a given amino acid and depends on the nature of R-linked to -carbon atom. (i) Action of heat (a) For -amino acids NH H OH OC  CO OH H HN H3NCHCOOC2H 5 2 pH 11 (Anion in fairly basic solution) pH 7 (Zwitter ion in neutral m edium) + Sodium salt C2H5OH Dry HCl ||   - Valerolactum  - Amino valeric acid (ii) -amino acids show the reactions of –NH2 group, –COOH groups and in which both the groups NaOH are involved. RCHNH2COON a |  |  60 + ||  heat CH 2 C H 2 CH 2 CH 2 CO   CH 2 CH 2 CH 2 CH 2 CO | ( H 2 O ) | O  H NH H NH E3 O  heat CH 2  CH 2  CH 2  CO   CH 2  CH 2  CH 2  CO ( H 2 O ) | | NH H NH H O PCl5 COOH NH 2(HCl) Salt formation R.CH COCl Amino acid chloride  Proline is the only natural -amino acid which is a secondary amine.  Only achiral -amino acid found in protein is glycine. (iii) Formation of proteins-peptide bond : Proteins are formed by joining the carboxyl group of one amino acid to the -amino group of another amino acid. The bond formed between two amino acids by Biomolecules 1439 the elimination of a water molecule is called a peptide linkage or bond. The peptide bond is simply another name for amide bond.  C OH  H  N   C  N   H 2 O || | || | H O O H Side chains may have basic groups or acidic groups as  NH 2 in lysine and –COOH in aspartic acid. The product formed by linking amino acid molecules through peptide linkages, CO  NH  , is called a peptide. Peptides are further designated as di, tri, tetra or penta peptides accordingly as they contain two, three, four or five amino acid molecules, same or different, joined together in the following fashions. Primary structure tells us nothing about the shape or conformation of the molecule. Most of the bonds in H || O | | R R bonds can assume free rotation about confirmed that each three dimensional conformation. The fixed configuration of a polypeptide skeleton is referred to as the secondary structure of a protein. It gives information : || ( H 2 O ) H 2 N  CH  C  OH  H  N  CH  C  OH   | protein molecules being single infinite number of shapes due to single bonds. However, it has been protein has only a single 60 O Peptide bond E3 Amine group of other amino acid Carboxy l group of one amino acid Because of these acidic and basic side chains, there are positively and negatively charged centres. Though the peptide linkage is stable, the reactivity is due to these charged centres in the side chains. H 2 N  CH  C  N  CH  C  OH  About the manner in which the protein chain is folded and bent; Peptide R linkage (Dipeptide)  About the nature of the bonds which stabilise this structure. O H | R O | || | ID || When the number of amino molecules is large, the product is termed polypeptide which may be represented as, (i) -helix : This structure is formed when the chain of -amino acids coils as a right handed screw (called -helix) because of the formation of hydrogen bonds between amide groups of the same peptide chain, i.e., NH group in one unit is linked to carbonyl oxygen of the third unit by hydrogen bonding. This hydrogen bonding between different units is responsible for holding helix in a position. The side chains of these units project outward from the coiled backbone. D YG U O  O  ||  ||  H 2 N  CH  C   NH  C H  C   NH  C H  COOH | | |     R R R  n Secondary structure of protein is mainly of two types (4) Composition : Composition of a protein varies with source. An approximate composition is as follows : Carbon 50-53%; hydrogen 6-7%; oxygen 23-25%; nitrogen 16-17%; Sulphur about 1%. Other elements may also be present, e.g., phosphorus (in nucleoproteins), iodine (in thyroid proteins) and iron (in haemoglobin). U (5) Structure of proteins : The structure of proteins is very complex. The primary structure of a protein refers to the number and sequence of the amino ST acids in its polypeptide chains (discussed in the formation of proteins). The primary structure is represented beginning with the amino acid whose amino group is free (the N-terminal end) and it forms the one end of the chain. Free carboxyl group (Cterminal end) forms the other end of the chain. Left side O O Right hand || || side H 2 N  CH  C  NH  C H  C  NH... CH  COOH | | | R R R  hand Other end One end (N-terminal end) (R, R, R …may be same or different) (C-terminal end) Such proteins are elastic, i.e., they can be stretched. On stretching weak hydrogen bonds break up and the peptide chain acts like a spring. The hydrogen bonds are reformed on releasing the tension. Wool and hair have -helix structure. (ii) -pleated sheet : A different type of secondary structure is possible when polypeptide chains are arranged side by side. The chains are held together by a very large number of hydrogen bonds between C = O and NH of different chains. Thus, the chains are bonded together forming a sheet. These sheets can slide over each other to form a three dimensional structure called a beta pleated sheet. Silk has a beta pleated structure. Globular proteins possess tertiary structure. In general globular proteins are very tightly folded into a compact spherical form. (6) Classification of proteins : According to chemical composition, proteins are divided into two classes 1440 Biomolecules (ii) Conjugated proteins : The molecules of conjugated proteins are composed of simple proteins and non protein material. The non-protein material is called prosthetic group or cofactor. These proteins on hydrolysis yield amino acids and non-protein material. Examples are Mucin in saliva (prosthetic group, carbohydrate), casein in milk (prosthetic group, phosphoric acid), haemoglobin in blood (prosthetic group, iron pigment), etc. According to molecular shape, proteins are divided into two types Protective proteins (antibiotics) Destroy any foreign substance released into the living system. Gamma Toxins Poisonous Snake venom. globulin. in nature. (7) General proteins and physical characteristic of (i) Most of them (except chromoproteins) are colourless, tasteless, and odourless. Many are amorphous but few are crystalline. They are nonvolatile and do not have a sharp melting point. (ii) Most of alcohol. But many dilute acids and keratins (skin, hair them are insoluble in water and of them dissolve in salt solutions, alkalies. Some proteins such as and nails) are completely insoluble. ID (i) Fibrous proteins : These are made up of polypeptide chains that run parallel to the axis and are held together by strong hydrogen and disulphide bonds. They can be stretched and contracted like a thread. These are usually insoluble in water. Examples are : keratin (hair, wool, silk and nails); myosin (muscles); collagen (tendons, bones), etc. system. 60 Egg albumin, serum globulins, glutenin in wheat, coryzenin in rice, tissue globulin, etc. in the living E3 (i) Simple proteins : Simple proteins are composed of chains of amino acid units only joined by peptide linkages. These proteins on hydrolysis yield only mixture of amino acids. Examples are : U (iii) Protein molecules are very complex and possess very high molecular masses. They are hydrophilic colloids which cannot pass through vegetable or animal membrane. On addition of sodium chloride, ammonium sulphate magnesium sulphate, etc., some proteins are precipitated. The precipitate can be filtered and redissolved in water. D YG (ii) Globular proteins : These have more or less spherical shape (compact structure). -helics are tightly held up by weak attractive forces of various types: Hydrogen bonding, disulphide bridges, ionic or salt bridges. These are usually soluble in water. Examples are: Insulin, pepsin, haemoglobin, cytochromes, albumins, etc. Proteins can also be classified on the basis of their function U Table : 31.6 Protein Examples Biological catalysts, vital to ST Enzymes Function Proteins that hold living systems Act messengers. as Transport proteins Carry ions or molecules from place to another  groups ( N H 3 and COO  ) at the ends of the peptide chain, are amphoteric in nature. In strong acid solution, protein molecule accepts a proton while in strong basic solution it loses a proton. The pH at which the protein molecule has no net charge is called its isoelectric point. This property can be used to separate Collagen. proteins from mixture by electrophoresis. together. Harmones (v) Isoelectric point : Every protein has a characteristic isoelectric point at which its ionisation is minimum. Like amino acids, proteins, having charged Trypsin, pepsin. all living systems. Structural proteins (iv) The solution of proteins are optically active. Most of them are laevorotatory. The optical activity is due to the presence of asymmetric carbon atoms in the constituent -amino acids. Insulin. Haemoglobin. (vi) Denaturation : The structure of the natural proteins is responsible for their biological activity. These structures are maintained by various attractive forces between different parts of the polypeptide chains. The breaking of these forces by a physical or a chemical change makes the proteins to lose all or part of their biological activity. This is called denaturation of proteins. The denaturing of proteins can be done by Biomolecules adding chemicals such as acids, bases, organic solvents, heavy metal ions, or urea. It can also be done with the help of heat and ultraviolet light. Denaturation can be irreversible or reversible. In irreversible denaturation, the denaturated protein does not return to its original shape. For example, the heating of white of an egg (water soluble) gives a hard and rubbery insoluble 1441 (iv) Ninhydrin test : This test is given by all proteins. When a protein is boiled with a dilute solution of ninhydrin, a violet colour is produced. (v) Nitroprusside test : Proteins containing –SH group give this test. When sodium nitroprusside solution is added to proteins having –SH group, a violet colour is developed. mass. O (8) Chemical properties || with acids and bases. Casein is present in milk as C calcium salt. || O Protein Proteose Peptone Polypeptide Simple peptide Mixture of amino acids D YG U (iii) Oxidation : Proteins are oxidised on burning and putrefaction. The products include amines, nitrogen, carbon dioxide and water. The bad smell from decaying dead animals is largely due to the formation of amines by bacterial oxidation of body proteins. (9) Test of proteins (i) Biuret test : On adding a dilute solution of copper sulphate to alkaline solution of protein, a violet colour is developed. This test is due to the presence of peptide (–CO–NH–) linkage. ST U (ii) Xanthoproteic test : Some proteins give yellow colour with concentrated nitric acid (formation of yellow stains on fingers while working with nitric acid in laboratory). The formation of yellow colour is due to reaction of nitric acid with benzenoid structures. Thus, when a protein solution is warmed with nitric acid a yellow colour may be developed which turns orange on addition of NH 4 OH solution. (iii) Millon’s test : When millon’s reagent (mercurous and mercuric nitrate in nitric acid) is added to a protein solution, a white precipitate which turns brick red on heating, may be formed. This test is given by proteins which yield tyrosine on hydrolysis. This is due to presence of phenolic group. | + RCCOOH | OH NH2 Amino acid Ninhydri n ID hydrolysis and the final product is a mixture of amino acids. OH C E3 (ii) Hydrolysis : The simple proteins are hydrolysed by acids, alkalies or enzymes to produce amino acids. Following steps are involved in the H 60 (i) Salt formation : Due to presence of both  NH 2 and –COOH groups in proteins, they form salts C O OH || | C C C = NC | C – C || R || O O Violet complex (vi) Molisch’s test : This test is given by those proteins which contain carbohydrate residue. On adding a few drops of alcoholic solution of -naphthol and concentrated sulphuric acid to the protein solution, a violet ring is formed. (vii) Hopkins-Cole test : On adding concentrated sulphuric acid down the side containing a solution of protein and glyoxalic acid, a violet colour is developed. (10) Uses (i) Proteins constitute as essential part of our food. Meat, eggs, fish, cheese provide proteins to human beings. (ii) In textile : Casein (a milk protein) is used in the manufacture of artificial wool and silk. (iii) In the manufacture of amino acids : Amino acids, needed for medicinal use and feeding experiments, are prepared by hydrolysis of proteins. (iv) In industry : Gelatin (protein) is used in food products, capsules and photographic plates. Glue (protein) is used as adhesive and in sizing paper. 1442 Biomolecules Leather is obtained by tanning the proteins of animal hides. (vi) As enzymes : Reactions in living systems always occur with the aid of substances called enzymes. Enzymes are proteins produced by living HN N H O Proteins Amino acids Nucleic acids In every living cell there are found nucleoproteins which are made up of proteins and natural polymers of great biological importance called nucleic acids. Two types of nucleic acids are found in biological systems, these are U Deoxyribonucleic acid (DNA) and Ribonucleic acid (RNA) ST The nucleic acid was first isolated by Friedrich Miescher in 1868 from the nuclei of pus cells and was named nuclein. The term nuclein was given by Altman. (1) Composition : Nucleic acids like proteins and carbohydrates are polymer. The simple units that make up the nucleic acid are called nucleotides. Nucleotides are themselves composed of following three simple molecules. (i) Nitrogenous base : These are heterocyclic organic compound having two or more nitrogen atoms in ring skeleton. These are called bases because the lone pairs of electrons on the nitrogen atoms make them as Lewis bases. Their structures are given below (a) Pyrimidine derivatives 4 3 N N H O 5-Hydroxy methyl cytosine NH2 N1 2 DNA, RNA Nucleotides D YG Nuclease 5-Methyl cytosine ID Trypsin H2CO3 H2O + CO2 N HO U Proteins Amino acids Carbonic anhydrase ; (b) Purine derivatives Pepsin 5 2 5-methyl pyrimidine NH 2 CH2O N H 3 Sucrose Glucose + Fructose Starch n Glucose CH- N Urea CO2 + NH3 Amylase o r HO N H O 2 Reaction catalysed Maltose 2 Glucose 4 NH Table : 31.7 Maltase ; N1 E3 (T) DNA Invertase 26 N Cytosine Cytosine (C) 2, 6 (C) dihydroxy pyrimidine OH O CH3 CH 6 5 H 1 3 N o 2 3 4 N N N r O HO H 2, 6 dihydroxy Thymine Uracil (U) RNA Important enzymes tabulated as under, Urease 5 o N1 2 3 r N HO systems and catalyse specific biological reactions. Enzymes NH 6 60 (v) In controlling body processes : Haemoglobin present in blood is responsible for carrying oxygen and carbon dioxide. Harmones (proteins) control various body processes. NH2 OH O 6 N 7 5 8 CH 3 4 OH 2 3 1 N H Adenine (A) DNA, RNA 6 4 5 H2N N 9 N ; N N 7 8 CH 9 N H Guanine (G) DNA, RNA (ii) Five carbon sugar (Pentose) : In RNA, the sugar is ribose where as in DNA, the sugar is 5 deoxyribose. CH2OH O OH 1 CHOH 1 4 C H H C or H C 3 HO H O 3 CHOH 4 CH 2 5 CH2OH OH Ribose 5 CH2OH O OH 1 CHOH 1 4 C H 2 CHOH C C H C 3 C 2 CH2 or H H 2 OH H Deoxyribose O 3 CHOH 4 CH 5 CH2OH Both differ only at carbon atom 2  in the ring. Biomolecules (iii) Phosphoric acid, H3PO4 : Phosphoric acid forms esters to –OH groups of the sugars to bind nucleotide segments together. A molecule called nucleoside is formed by condensing a molecules of the base with the NH (i.e., Base + Sugar). appropriateNpentose. 5 CH2OH C H C3 C H H N N C H H C C 3 C2 H 2 HO OH Adenosine (nucleoside)  HO 1 4 – H2O 1 C H CH2OH O OH 2 N 5 4 H NH N OH Ribose Thus, the formation of a nucleic acid can be summarised in the following general way | 5 HO — P — O — CH2 || 4 C O O N 1 N D YG C U ID A nucleotide results when the nucleoside combined with phosphoric acid mainly at carbon 5 of NH2 the pentose. (i.e., Base + Sugar + Phosphoric acid). N OH N H 60 N | H + O N Adenin N e of the nucleotide monomers and are formed by the creation of an ester linkage from phosphoric residue on one nucleotide to the hydroxy group on carbon 3 in the pentose of the second nucleotide. The result is a very long chain possessing upto a billion or so nucleotides units in DNA. E3 2 1443 H H C C 3 H 2 HO OH Nucleotide-adenosine 5-phosphoric acid Sugar (Ribose Base (Purine or deoxy ribose) or pyrimidine) Nucleoside Phosphoric acid Nucleotide Poly Nucleotide (Nucleic acid) ST U This nucleotide is the building block of both DNA and RNA. The nucleic acids are condensation polymers RNA nucleotides Base + Ribose (Nucleoside) + Phosphoric acid Nucleotide Adenine + Ribose (Adenosine) + Phosphoric acid Adenylic acid Guanine + Ribose (Guanosine) + Phosphoric acid Guanylic acid Cytosine + Ribose (Cytidine) + Phosphoric acid Cytidylic acid | Uracil + Ribose (Uridine) + Phosphoric acid Uridylic acid HO – P – O – Sugar – DNA nucleotides Base Adenine + Deoxy ribose sugar + Phosphate Adenosine phosphate || | Guanine| + Deoxy ribose sugar + Phosphate Guanosine phosphate O O HO – P – + O – Deoxy Sugar ribose – Cytosine sugar + Phosphate Cytosine phosphate Base Thymine + Deoxy ribose sugar + Phosphate Thymidine phosphate || | and highly complex, spirally twisted, double helix, (2) Structure : The sequence of bases along the |O O establishes ladder like structure. The two polynucleotide chains or DNA and RNA chain its primary structure HO – P – O – Sugar – strands are linked up by hydrogen bonding between the which controls the specific properties of the nucleic Base nitrogenous base molecules of their nucleotide acid. An RNA molecule is usually a single chain of || | monomers. Adenine (purine) always links with thymine ribose-containing nucleotides. DNA molecule is a long O O Biomolecules and C (adenine, thymine, guanine and cytosine) in the DNA molecule. The sequence of bases in one chain of the double helix controls the sequence in other chain. The two chains fit together like a hand and a glove. They separate and about the hand is formed a new glove, and inside the glove is formed a new hand. Thus, the pattern is preserved in the two new molecules of DNA. 60 [If one strand of DNA has the sequence ATGCTTGA, then the sequence of complimentary strand will be TACGAACT]. E3 (ii) Synthesis of proteins : The DNA contains the genetic code and directs protein synthesis through RNA. The double helix of DNA partially uncoils and about the individual strands are formed chains of RNA. The new chains contain ribose instead of deoxyribose and the base sequence is different which is determined by DNA, i.e., opposite each adenine of DNA, there appears on RNA a uracil; opposite guanine, cytosine; opposite thymine, adenine, opposite cytosine, guanine. Thus, AATCAGTT on DNA becomes UUAGUCAA on RNA. ID (pyrimidine) with the help of two hydrogen bonds and guanine (purine) with cytosine (pyrimidine) with the help of three hydrogen bonds. Hence, the two strands extend in opposite directions, i.e., are antiparallel and complimentary. The following fundamental relationship exist.  Thymine combines only with deoxyribose sugar and uracil only with ribose sugar. Other bases can combine with either of the two sugars.  The sum of purines equals the sum of pyrimidines.  The molar proportion of adenine equals to that of thymine.  The molar proportion of guanine equals to that of cytosine.  The double helix is 20 Å. It completes a spiral at every 10 nucleotide pairs at a length of 34 Å. Sequences of monomers (nucleotides) may present innumerable variations. Evidently, innumerable varities of DNA exist in the organism.  Watson, Crick and Witkins were awarded Noble prize in 1962 for suggesting the structure of DNA. 1443 U 20 A° One kind of RNA, called messenger RNA, carries a message to the ribosome, where protein synthesis actually takes place. At the ribosome, messenger RNA calls up a series of transport RNA molecules, each of which is loaded with a particular amino acid. The order in which the transport RNA molecules are called (–the sequence in which the amino acids are arranged to form the protein chain) depends upon the sequence of bases along the messenger RNA chain. Thus GAU is the code for aspartic acid; UUU, phenyl alanine; GUG, valine. There are 64-three letter code words (codons) and only 20-odd amino acids, so that more than one codon call the same amino acid. D YG Shallo w groove 3.4 A° One spiral 3.4 A° Deep 10 groove A° Major axis Shallo w groove Fig :31.1 Helical structure of DNA as suggested by Watson and Crick U Table : 31.8 Difference between DNA and RNA ST DNA It has a double helix structure. Sugar unit is deoxyribose. Base units are adenine, guanine, thyamine and cytosine. Responsible for inheritance of character. RNA It has a single helix structure. Sugar unit is Ribose. It contains uracil base instead of thyamine, other bases being same as those in DNA. It is responsible for protein synthesis. (3) Functions of nucleic acid : Nucleic acid have two important functions (i) Replication and (ii) Protein synthesis. (i) Replication : The genetic information for the cell is contained in the sequence of the bases A, T, G The relation between the nucleotide triplets and the amino acids is called Genetic code. Nirenberg, Hollay and Khorana presented the genetic code for which they were awarded Noble prize in 1968. (4) Mutation : A mutation is a chemical or physical change that alters the sequence of bases in DNA molecule. Anything that causes mutation is called mutagen. A mutation results from ultraviolet light, ionisation radiations, chemicals or viruses. The changes in sequence of bases in DNA are repaired by special enzymes in the cell. If it is not, the protein produced has no biological activity and the cell dies. These mutations often prove harmful and give rise to symptoms that cause diseases. Sickle-cell anaemia is one such example. Such disease is passed on from one generation to the next generation. Lipids Lipids are constituents of plants and tissues which are insoluble in water but soluble in organic 1444 Biomolecules E3 60 phospholipids good emulsifying and membrane forming properties. Cell membranes are composed of phopholipids and proteins in about equal, proportion. The phospholipids in the membrane appear to be arranged in a double layer or bilayer in which the non-polar tails face each other, thereby exposing the polar heads to the aqueous environment on either side of the membrane. Proteins found in the membrane are embedded in the mossaic formed by the lipids. Phospholipids facilitate the transport of ions and molecules in and out of the cell and regulate the concentration of molecules and ions within the cell. They provide structural support for certain proteins. The above mentioned lipids are mainly straight chain compounds. There is a third class of lipids which are not straight chain compounds. They are called Sterols. The sterols are composed of fused hydrocarbon rings and a long hydrocarbon side chain. Cholestrol is most important compound of this class and is found in animals only. It exists either free or as ester with a fatty acid. Cholestrol is also the precursor of hormones. Cholestrol and its esters are insoluble in water. So they are deposited in the arteries and veins if the blood cholestrol rises. This leads to high blood pressure and heart diseases. Cholestrol is a part of animal cell membrane and is used to synthesized steroid hormones, vitamin-D and bile salts. ST U D YG U ID solvents such as chloroform, carbon tetrachloride, ether or benzene. They include a large variety of compounds of varying structures such as oils and fats; phospholipids, steroids, etc. Lipids are mainly made of carbon, hydrogen and oxygen. The number of oxygen atoms in a lipid molecule is always small as compared to the number of carbon atoms. Sometimes small amounts of phosphorus, nitrogen and sulphur are also present. They have a major portion of their structure like a hydrocarbon (aliphatic or fused carbon rings). Lipids serve as energy reserve for use in metabolism and as a major structural material in cell membranes for regulating the activities of cell and tissues. Simple lipids are esters of glycerol with long chain monocarboxylic acids which can be saturated or unsaturated. These are generally called glycerides of fats and oils. Waxes are esters of fatty acids with certain alcohols, not glycerol. Fats and oils have biological importance but waxes have no value as these are not digested. The functions of triglycerides are the following (1) They are energy reserves in the cells and tissues of living system. When digested, triglycerides are hydrolysed to fatty acids and glycerol. (2) Catabolism of fatty acids form acetylcoenzyme-A. Most of the energy of fatty acids is converted into ATP. (3) Acetyl coenzyme is the starting material for the synthesis of many compounds. (4) Fats deposited beneath the skin and around the internal organs minimize loss of body heat and also act as cushions to absorb mechanical impacts. Another very important class of lipids are the phospholipids. These are polar lipids and like the fats, are esters of glycerol. In this case, however, only two fatty acid molecules are esterified to glycerol, at the first and second carbon atom. The remaining end position of the glycerol is esterified to a molecule of phosphoric acid, which in turn is also esterified to Rgives a general structure. another alcohol. This | O | O = P – O – CH2 O | | || OH CH – O – C – R | CH2O – C – R || O The alcoholic compound linked to phosphoric group may be choline, ethanol, amine, serine or inositol. The phosphate groups forms a polar end, i.e., hydrophilic (water-attracting) and the two fatty acid chains constitute the non-polar tail, i.e., hydrophobic (water repelling). This structure gives the Energy cycle or metabolism A cell has small molecules (micromolecules) as well as large molecules (macromolecules). The chemical reactions of a living organism can be divided into main two types (1) The chemical reactions by which the large molecules are constantly broken down into smaller ones are called catabolism. (2) The chemical reactions by which the macromolecules are synthesised within the cell are called anabolism. The two processes i.e., degradation and synthesis are collectively called metabolism. Catabolism reactions are usually accompanied by release of energy whereas anabolism reactions require energy to occur. The primary energy found in living cells is chemical energy, which can be easily stored, transferred and transformed. For this, the living cells contain a chemical compound called adenosine triphosphate (ATP). It is regarded as energy currency of living cells because it can trap, store and release small packets of energy with ease. ATP consists of a purine base called adenine linked to a five carbon sugar named ribose which is further attached to three molecules of phosphate. ATP is energy rich molecule this is because of the presence of four negatively charged oxygen atom very close to each other. These four negatively charged oatoms experience very high repulsive energy. NH2 O– O– N C O– | | | O– — P~O– P~O—P—O— CH2 || || || O O HC O C N C N O H C H N CH Biomolecules 1445 passes through a long passage in the body called alimentary canal. During this passage it gets mixed with various enzymes in different parts of the alimentary canal. The carbohydrates, proteins and fats are converted into simpler forms which are then carried by blood to different parts of the body for utilization. Digestion of food can be summarized in the following form Amy lase  Disaccharides (1) Polysaccha ride  Hy droly sis ATP    ADP  Pi H = –30.93 kJ mol–1 Maltase Disacchari des (maltose, etc.)   Glucose Adenosine diphosphat e Hy droly sis ADP    AMP Adenosine monophosph ate 60  Saliva (mouth);   Pancreatic juice  (Intestine )   (Intestine ) (2) Pepsin/ HCl Try psin Proteins    Proteases and Peptones    2 Pi H = –28.4 kJ mol–1  Chemotry ps in   Pancreatic juice  (Intestine )    (Stomach) E3 ADP can change to ATP in the presence of inoraganic phosphate. This process is called phosphorylation. Peptidases Peptides    Amino acids (Intestine ) ATP Lipases (3) Fats  Emulsified fat    Fatty acids (From liver)  Pancreatic and   intestine juice     Glycerol Bile salts Doing work  phosphate Loses ADP phosphate Fuels Vitamins D YG Digestion of food U group O2 After digestion, there are present glucose, aminoacids, fatty acids along with vitamins and mineral salts. Undigested food and secretions are pushed forward into the rectum from where these are excreted. ID Gains inorganic Catabolism In addition to air, water, carbohydrates, proteins, fats and mineral salts, certain organic substances required for regulating some of the body processes and preventing certain diseases are called vitamins. These compounds cannot be synthesised by an organism. On the basis of solubility, the vitamins are divided into two groups. (1) Fat soluble; Vitamin A, D, E and K. (2) Water soluble; Vitamin B and C. ST U Digestion is the process by which complex constituents of food are broken down into simple molecules by a number of enzymes in mouth, stomach and small intestine. The simple molecules thus formed are absorbed into blood stream and reach various organs. Raw food may be taken as such or after cooking. It is chewed in the mouth and swallowed when it Table : 31.9 Name Sources Functions Water soluble vitamins Vitamin B1 Rice polishings, wheat Major component of coco-carboxylase (Thiamine or Aneurin) flour, oat meal, eggs, yeast, enzyme meat, liver, etc. required for carbohydrate (C12H18N4SOCl2) and amino acid metabolism. Vitamin B2 or G Cheese, eggs, yeast, Combines with (Riboflavin or tomatoes, green vegetables, phosphoric acid to form liver, meat, cereals, etc. coenzyme FAD essential Lactoflavin) for oxidative metabolism. (C17H20N4O6) Vitamin B3 (Pantothenic acid) (C9H17O5N) All food; more in yeast, liver, kidneys, eggs, meat, milk, sugarcane, groundnut, tomatoes. Important component of Co-A required for oxidative metabolism. Effects of defficiency Beri-beri, loss of appetite and vigour, constipation, weak heart beat, muscle atrophy, even paralysis. Cheilosis, digestive disorders, burning sensations in skin and eyes, headache, mental depession, scaly dermatitis at angles of nares, corneal opacity, etc. Dermatitis, in cocks; greying of hairs, retarded body and mental growth, reproductive debility. Biomolecules 1445 Fresh meat, liver, fish, cereals, milk, pulses, yeast, etc. Active group in coenzyme NAD required for oxidative metabolism. Pellagra, dermatitis, diarrhoea, demenia, muscle atrophy, inflammation of mucous membrane of gut. Milk, cereals, fish, meat, liver, yeast synthesised by intestinal bacteria. Important coenzyme required in protein and amino acid metabolism. Vitamin H (Biotin) (C10H16N2O3S) Yeast, vegetables, fruits, wheat, chocolate, eggs, groundnut synthesised by intestinal bacteria. Green vegetables, soyabean, yeast, kidneys, liver, synthesised by intestinal bacteria. Meat, fish, liver, eggs, milk synthesised by intestinal bacteria. Essential for fat synthesis and energy production. Dermatitis, anaemia, convulsions, nausea, insomnia, vomiting, mental disorders, depressed appetite. Skin lesions, loss of appetite, weakness, hairfall, paralysis. Lemon, orange and other citrus fruits, tomatoes, green vegetables, potatoes, carrots, pepper, etc. Retarded growth, pernicious anaemia Essential for formation of collagen, cartilage, bone, teeth, connective tissue and RBCs and for iron metabolism. Wound-healing and growth retarded, scurvy, breakdown of immune defence system, spongy and bleeding gums, fragile blood vessels and bones, exhaustion, nervous breakdown, high fever. E3 Required for chromosome duplication and formation of blood corpuscles. D YG Fat soluble vitamins Vitamin A (Retinol or Axerophthol) (C20H30O) Retarded growth, anaemia. ID Vitamin B12 (Cyanocobalamine) (C63H88O14N14PCo) Vitamin C (Ascorbic acid) (C6H8O6) Essential for synthesis of DNA and maturation of blood corpuscles. U Folic acid group 60 Vitamin B5 or P-P (Nicotinic acid or Niacin) C6H5NO2 (C5H4N– COOH) Vitamin B6 (Pyridoxine or Adermin) (C8H11O3N) Essential for synthesis of visual pigments; growth and division of epithelial cells. Xerophthalmia-keratini-zed conjunctive and opaque and soft cornea. Stratification and keratinization in epithelia of skin, respiratory passages, urinary bladder, ureters and intestinal mucosa, night-blindness, impaired growth, glandular secretion and reproduction. Synthesised in skin cells in sunlight from 7-dehydrocholesterol also found in butter, liver, kidneys, egg yolk, fish oil, etc. Green vegetables, oil, egg yolk, wheat, animal tissues. Regulates absorption of calcium and phosphorus in intestine, mineral deposition in bones and teeth. Essential for proper spermatogenesis, pregnancy, lactation and muscular function. Rickets with osteomalacia; soft and fragile teeth. Carrots, lettuce, cabbage, tomatoes, liver, egg yolk, cheese; synthesized by colon bacteria. Essential for synthesis of prothrombin in liver, which is required for blood clotting. Haemorrhages, excessive bleeding in injury, poor coagulation of blood. U Synthesised in cells of liver and intestinal mucous membrane from carotenoid pigments found in milk, butter, kidneys, egg yolk, liver, fish oil, etc. ST Vitamin D (Ergocalciferol), (Sun shine vitamin) C28H44O and cholecalciferol Vitamin E group Tocopherols (, , ) (C29G50O2) Vitamin (Phylloquinone) (C31H46O2) K Sterility (impotency) and muscular atrophy. A Unique Book For Competition 1446 C1 and C2 in aldoses in ketoses are called anomers. Thus -D glucose and -D glucose are anomers and so are -D fructose and -D fructose.  Monosaccharides which differ in configuration at a carbon atom other than the anomeric carbon are called epimers. Thus glucose and mannose which differ in configuration at C2 are called C2 epimers while glucose and galactose which differ in configuration at C4 are called C4 epimers.  In amino acids –COO– group acts as the base while micro organisms and is conserved in the liver. Vitamin B12 has been found in rain water where its presence is attributed to micro organisms sucked up by the winds. 60  Monosaccharides which differ in configuration at   N H 3 acts as the acid. amino acids arranged in two polypeptide chains containing 21 and 30  amino acids residues respectively. The two peptide chains are held together by two cystine disulphide cross links.  Certain enzymes are associated with coenzymes U ID mostly derived from vitamins for their biological activity.  Each segment of a DNA molecule that codes for a specific protein or a polypeptide is called gene and the relationship between the nucleotide triplet and the amino acids is called the genetic code. E3  Insulin is a protein harmone. It consists of 51  Phospholipids are major constituents of cell walls. D YG  The deficiency of essential amino acids causes the disease called kwashiorkor.  Lecithin (present in eggs) and cephalins are phospholipids in which two of the hydroxyl groups of glycerol are esterified with palmitic acid whereas the third OH group in lecithin is esterified with chlone (CH3)3N+ – CH2CH2OH while in cephalin it is  esterified with ethanolamine, N H 3 CH 2 CH 2 OH.  Adenosine (ribose + adenine) is a nucleoside U while adenosine monophosphate (AMP), adenosine diphosphate and adenosine triphosphate (ATP) are all nucleotides. ST  Haemoglobin is a globular protein and the red colour of haemoglobin is due to protoporphyrin complex called the heme. the iron  The bicarbonate/carbonic acid system i.e., HCO3– /H2CO3 acts as the buffer and maintains the pH of blood between 7.36-7.42.  Vitamin C is a derivative of monosaccharide i.e., glucose while Vitamin D is derivative of steroid i.e. ergosterol.  Vitamin K and Vitamin A contain isoprene units.  Of all the vitamins, Vitamin B12 does not occur in plants but occurs only in animals and micro organisms. In fact, it is exclusively synthesized by the