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BIOMOLECULES, , , , , , . INTRODUCTION, , Complex organic compounds which govern the common, activities of the living organisms are called biomolecules., Living systems are made up of various complex biomolecules, like carbohydrates, proteins, nucleic acids, lipids, etc. In, addition, some simple molecules like vitamins and mineral, salts also play an important role in the functions of organisms., , 2. CARBOHYDRATES, , Carbohydrates are primarily produced by plants and form a, very large group of naturally occurring organic compounds., Some common examples are cane sugar, glucose, starch etc., Most of them have a general formula, CH, O. and were, considered as hydrates of carbon from where the name, carbohydrate was derived. For example, the molecular formula, of glucose (C 6H,,0,) fits into this general formula, C (H,0),., But all the compounds which fit into this formula may not be, classified as carbohydrates. Rhamnose, C,H,,0, is a, carbohydrate but does not fit in this definition. Chemically,, the carbohydrates may be defined as optically active, polyhydroxy aldehydes or ketones or the compounds which, produce such units on hydrolysis. Some of the carbohydrates,, which are sweet in taste, are also called sugars. The most, common sugar, used in our homes is named as sucrose, whereas the sugar present in milk is known as lactose., , 2.1 Classification of Carbohydrates, , Carbohydrates are classified on the basis of their behaviour, on hydrolysis. They have been broadly divided into, following three groups :, , 2.1.1 Monosaccharides, , A carbohydrate that cannot be hydrolysed further to give, simpler units of polyhydroxy aldehyde or ketone is called a, monosaccharide. Some common examples are glucose,, fructose, ribose, etc., , Monosaccharides are further classified on the basis of, number of carbon atoms and the functional group present, in them. Ifa 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, , Different types of Monosaccharides, , , , Carbon ee Aldehyde Ketone, FNC) Term =, 3 Triose Aldotriose Ketotriose, 4 Tetrose Aldotetrose | Ketotetrose, 5 Pentose | Aldopentose | Ketopentose, 6 Hexose | Aldohexose | Ketohexose, 7 Heptose | Aldoheptose | Ketoheptose, , , , , , 2.1.2 Oligosaccharides, , Carbohydrates that yield two to ten monosaccharide units,, on hydrolysis, are called oligosaccharides. They are further, classified as disaccharides, trisaccharides, tetrasaccharides,, etc., depending upon the number of monosaccharides, they, provide on hydrolysis. Amongst these the most common are, disaccharides. The two monosaccharide units obtained on, hydrolysis of a disaccharide may be same or different. For, example, sucrose on hydrolysis gives one molecule each of, glucose and fructose whereas maltose gives two molecules, of glucose only., , 2.1.3 Polysaccharides, , Carbohydrates which yield a large number of monosaccharide, units on hydrolysis are called polysaccharides. Some common, examples are starch, cellulose, glycogen, gums, etc., Polysaccharides are not sweet in taste, hence they are also, called non-sugars., , 2.1.4 Reducing and Non-Reducing Sugars, , The carbohydrates may also be classified as either reducing, , or non-reducing sugars. All those carbohydrates which, reduce Fehling’s solution and Tollens’ reagent are referred, , to as reducing sugars. All monosaccharides whether aldose, or ketose are reducing sugars., , In disaccharides, if the reducing groups of monosaccharides, ie., aldehydic or ketonic groups are bonded, these are nonreducing sugars e.g. sucrose. On the other hand, sugars in, which these functional groups are free, are called reducing, sugars, for example, maltose and lactose.

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(F), , Note., , my, , Reaction with phenylhydrazine (formation of osazone), , CHO CH=N—NH—Ph, , CH—OH — 3ph—NH—NH, oe, ee, , be sE5, in, , CH,OH wars, , Glucosazone, , One mole consumes three moles of PANHNH,, to form osazone. 2 moles give hydrazone group, ; and one is used to oxidise CHOH group to, , =O., , 3.3 Configuration in Monosaccharides, , Glucose is correctly named as D(+)-glucose. ‘D’ before the, name of glucose represents the configuration whereas ‘(+)’, represents dextrorotatory nature of the molecule. It may be, remembered that ‘D’ and ‘L’ have no relation with the optical, activity of the compound. The meaning of D- and, L— notations is given as follows. The letters ‘D’ or ‘L’ before, the name of any compound indicate the relative configuration, ofa particular stereoisomer. This refers to their relation with, a particular isomer of glyceraldehyde. Glyceraldehyde, contains one asymmetric carbon atom and exists in two, enantiomeric forms as illustrated., , CHO CHO, won onto, CH,OH CH,OH, , (+)-Glyceraldehyde (-)-Glyceraldehyde, , All those compounds which can be chemically correlated to, (+) isomer of glyceraldehyde are said to have D-configuration, whereas those which can be correlated to (-) isomer of, glyceraldehyde are said to have L-configuration. For, assigning the configuration of monosaccharides, it is the, lowest asymmetric carbon atom (as shown below) which is, compared. As in(+) glucose, -OH on the lowest asymmetric, carbon is on the right side which is comparable to (+), glyceraldehyde, so it is assigned D-configuration. For this, comparison, the structure is written in a way that most, oxidised carbon is at the top., , 1 hg, H—t+— OH Cc, H—+— OH HOH, Ho-}+-H | —»HO—+H |__.HO, H—+- on H—*+o, s H—~_ou, , CHO, , , , H—;—0H, CHO HO—+—-H, non H—;— OH, CH,OH H—+— On, D-~+)-Glyceraldehyde, CH,OH, D-(+)-Glucose, , 3.4 Cyclic Structure of Glucose, , , , Glucose is found to exist in two different crystalline forms which, are named as a and f. The o-form of glucose (m.p. 419 K) is, obtained by crystallisation from concentrated solution of glucose, at 303 K while the B-form(m_p. 423 K) is obtained by crystallisation, from hot and saturated aqueous solution at 371 K., , Both a-D-glucose and B-D-glucose undergo mutarotation, in aqueous solution. Although the crystalline forms of aand B-D (+)-glucose are quite stable in aqueous solution, but each form slowly changes into an equilibrium mixture of, both. This is evident from the fact that the specific rotation, of a freshly prepared aqueous solution of a-D(+)-glucose, falls gradually from +111° to +52.5° with time and that of, f-D(+)-glucose increases from +19.2° to 52.5°. Thus,, , a-D(+)-Glucose —— Equilibrium mixture, , eek = + 111°, , (al; [a]y™ = + $2.5°, , |, , B-D(+)-Glucose, , [a}o"* = + 19.2°, , This spontaneous change in specific rotation of an optically, active compound with time, to an equilibrium value, is called, mutarotation., , It was found that glucose forms a six-membered ring in which, —OH at C-S is involved in ring formation. This explains the, absence of -CHO group and also existence of glucose in, two forms as shown below. These two cyclic forms exist in, equilibrium with open chain structure.

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The two cyclic hemiacetal forms of glucose differ only in, , the configuration of the hydroxyl group at C ,, called anomeric, carbon (the aldehyde carbon before cyclisation). Such, isomers, L.e., a-form and B-form, are called anomers. The six, membered cyclic structure of glucose is called pyranose, structure (a— or B-), in analogy with pyran. Pyran is acyclic, organic compound with one oxygen atom and five carbon, atoms in the ring. The cyclic structure of glucose is more, correctly represented by Haworth structure., , , , , , , , OH, B-D-(+)-Glucopyranose, , H OH H, , a-D-(+)-Glucopyranose, , , , , , 3.4.1 How to draw a Haworth Projection, , Aring of 6 atoms (5 ‘C’ and | *O’) is drawn in which ‘O’ atom, is placed at right hand top corner as shown below, , +—oO, 4 l, 3 2, Carbon atom at the right hand side of oxygen is given number, 1. Then other carbon atoms are given numbers 2, 3 ......... in, , a clockwise fashion. Groups attached to a carbon in Fischer, projection lying on the right hand side of that carbon are, placed below the ring and on the left hand side are placed, above the ring. But CH,OH group of carbon 5 is placed, above the plane of ring by convention, , , , , , , , , , , , 6, H—C-OH CH,OH, H—=—-OH, ee, HOH =, H—*+0H, H 5 2, H OH, *CH,OH, , Haworth Projection, of a-D-Glucose, , a-D-Glucose, , , , 4. FRUCTOSE (KETOHEXOSE), , Fructose also has the molecular formula C,H,,0, and on, the basis of its reactions it was found to contain a ketonic, functional group at carbon number 2 and six carbons in, straight chain as in the case of glucose. It belongs to, D-series and is a laevorotatory compound. It is appropriately, , written as D-(—)-fructose. Its open chain structure is as shown, , pes, , *~c=0, , 3, , HO—C—H, , H—cC—OH, , s|, H—C—OH, , “CH,OH, , Fructose, , It also exists in two cyclic forms which are obtained by the, ee %, addition of -OH at C5 to the ye group. The ring,, , thus formed is a five membered ring and is named as furanose, with analogy to the compound furan. Furan is a five membered, cyclic compound with one oxygen and four carbon atoms., , , , , , , , , , , , , , , , , , C, Furan, 1 2 2 1, HOH,C—C—OH HO—C—CH,OH, HO--H O HoH O, H—+—OH H—+— OH, H— H—, 6 6, CH,OH CH,OH, , a-D-(—)-Fructofuranose §-D-(—-)-Fructofuranose, , The cyclic structures of two anomers of fructose are, represented by Haworth structures as given., , oO oO, , 6 1 6, HOH,C CH,OH HOH,C, , , , OH H, , B-D-(--)-Fructofuranose, , OH H, , a-D-(--)-Fructofuranose