Tiêu đề BIOMOLECULES, POLYMERS & CHEMISTRY IN EVERYDAY LIFE.pdf ✅

 Digital www.allendigital.in [ 155 ] Biomolecules Biomolecules are chemical compounds which are building blocks of life and perform important functions in living organisms. The general biomolecules that our food contains are : Biomolecules • Carbohydrates • Proteins • Enzymes • Vitamins • Nucleic acids • Hormones 1. Carbohydrate : General formula of carbohydrate can be written as Cx (H2O)y Here, x = y or x ≠ y Hence these are called, Hydrates of carbon Exceptions • Rhamnose (C6H12O5) is a carbohydrate, but it does not fit in this formula. • Acetic acid (CH3COOH) is not a carbohydrate, but it fits in this formula. Simplest ratio ⎯⎯→ C : H : O 1 : 2 : 1 1. Glucose ⎯→ Mol. Formula (C6H12O6) Glucose ⎯→ C6 (H2O)6 2. Sucrose ⎯→ Mol. Formula (C12H22O11) Sucrose ⎯→ C12 (H2O)11 New definition of carbohydrates Optically active polyhydroxy aldehydes and polyhydroxy ketones or compounds which give such compounds on hydrolysis are called carbohydrates. Only dihydroxy acetone is optically inactive carbohydrate. CH2OH C O CH2OH Carbohydrates are also called saccharides (greek word: saccharon means sugar). Classification of Saccharides on the basis of behaviour on hydrolysis :- • Monosaccharides • Oligosaccharides • Polysaccharides Biomolecules, Polymers and 06 Chemistry in Everyday Life
NEET : Chemistry [ 156 ] www.allendigital.in  Digital Monosaccharides • A carbohydrate that cannot be hydrolysed further to give simpler unit of polyhydroxy aldehyde or ketone is called a monosaccharide. • About 20 monosaccharides are known to occur in nature. Example: glucose, fructose, ribose, etc. Monosaccharides are further classified on the basis of number of carbon atoms and the functional group present in them. If a monosaccharide contains an aldehyde group, it is known as an aldose and if it contains a keto group, it is known as a ketose. Number of carbon atoms constituting the monosaccharide is also introduced in the name as is evident from the examples given in table. No. of Carbon Atoms Aldose (these contain aldehyde functional group) Ketose (these contain ketone functional group) 3 Aldotriose = Glyceraldehyde Ketotriose = Dihydroxy ketone 4 Aldotetrose = Erythrose Ketotetrose = Erythrulose 5 Aldopentose = Ribose Ketopentose = Ribulose 6 Aldohexose = Glucose Ketohexose = Fructose 7 Aldoheptose = Manohaptose Ketoheptose = Sedoheptulose Oligosaccharides • Carbohydrates that yield two to ten monosaccharide units on hydrolysis, are called oligosaccharides. • They are further classified as disaccharides, trisaccharides, tetrasaccharides etc. depending upon the number of monosaccharides which provide on hydrolysis. Example: sucrose (glucose + fructose), maltose (glucose + glucose) etc. Polysaccharides Carbohydrates which yield a large number of monosaccharide units on hydrolysis are called polysaccharides. Some common examples are starch, cellulose, glycogen, etc. Polysaccharides are not sweet in taste, hence they are also called non-sugars. The carbohydrates may also be classified as either reducing or non-reducing sugars. Reducing sugars 1. They reduce Fehling solution and Tollen’s reagent 2. All monosaccharides & disaccharides in which aldehydic and ketonic groups are free, behave as reducing sugars. Example : Glucose, Fructose, Maltose & lactose. Non-reducing sugars 1. They do not reduce Fehling’s solution and Tollen’s reagent. 2. All polysaccharides & disaccharides in which aldehydic or ketonic groups are bonded behave as non-reducing sugars. Example : Sucrose, Starch, Glycogen
Biomolecules, Polymers and Chemistry in Everyday Life  Digital www.allendigital.in [ 157 ] Monosaccharides Glucose 1. Laboratory Method From Sucrose (Cane sugar) On hydrolysis of sucrose, the sign of rotation changes from dextro (+) to laevo (–), so sucrose is called invert sugar. 2. Commercial Method From Starch (C6H10O5)n + H2O H + nC6H12O6 Starch Glucose 393 K; 2-3 atm Chemical reactions of Glucose (a) Reaction with NH2OH CHO (CHOH)4 NH2OH CH2OH CH=N—OH (CHOH)4 CH2OH Glucose oxime (b) Reaction with HCN CHO (CHOH)4 HCN CH2OH CH (CHOH)4 CH2OH Glucose cyanohydrin OH CN (c) Oxidation Oxidation of glucose to six carbon carboxylic acid (gluconic acid) indicates that the carbonyl group is present as an aldehydic group. (i) Oxidation with Br2 water CHO (CHOH)4 Br2 water CH2OH COOH (CHOH)4 CH2OH Gluconic acid (ii) Oxidation by Tollen’s Reagent, Fehling solution and Benedict’s solution CHO (CHOH)4 Tollen’s reagent CH2OH COOH (CHOH)4 CH2OH Gluconic acid + Ag Silver mirror C12H22O11 + H2O H2SO4 or HCl C6H12O6 + C6H12O6 Sucrose Glucose Fructose 'd' +66.5° 'd' +52.5° '' –92.4°
NEET : Chemistry [ 158 ] www.allendigital.in  Digital CHO (CHOH)4 Fehling / Benedict Sol. CH2OH COOH (CHOH)4 CH2OH Gluconic acid + Cu2O Red precipitate Oxidation of glucose to six carbon containing di carboxylic acid indicates the presence of primary Alcohol group. (iii) Oxidation by conc. HNO3 CHO (CHOH)4 Oxidation by HNO3 CH2OH COOH (CHOH)4 COOH Saccharic acid Oxidation by HNO3 COOH (CHOH)4 CH2OH Glucose Gluconic acid (d) Acetylation of glucose with acetic anhydride gives glucose penta acetate which confirms the presence of five –OH groups CHO (CHOH)4 Acetic anhydride CH2OH CHO (CH–O—C—CH3)4 CH2–O–C–CH3 Glucose penta acetate O O (e) Reaction with Phenyl Hydrazine (Osazone formation) When carbohydrates react with excess of phenyl hydrazine then osazone is formed CHO H—C—OH + 3Ph—NH—NH2 Glucosazone HO—C—H H—C—OH H—C—OH CH2OH CH=N—NH—Ph HO—C—H H—C—OH H—C—OH CH2OH C=N—NH—Ph + NH3 + Ph—NH2 + H2O Open chain structure of Glucose The exact spatial arrangement of different –OH groups was given by Fischer after studying many other properties. Glucose is correctly named as D(+)-glucose. The meaning of D– and L– notations is given as follows. CHO CH2OH H OH D – (+) – Glyceraldehyde CHO CH2OH HO H L – (–) – Glyceraldehyde Structure of Glucose Open chain structure Cyclic Structure