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Biomolecules28
Chapter
CD CARBOHYDRATES 0 Carbonyl group present Is an aldehyde Is confi~ed by d
c&asslficatlon ofCarbohydrates:
A. Monosaccharldes: A carbohydrate that cannot be
hydrolysed further to give simpler unit of polyhydroxy
aldehyde or ketone. Examples: Glucose, fructose,
arabinose etc.
the given reaction ·
CHO
I
(CHOH)4
I
CH20H
Br2
COOH
I
I
CH20H
·
H • (CHOH)4 (Gluconic acid)
20
a Acetylation of glucose gives glucose pentaacetate which
H~
H
H---~
~~
OH
o_:ir~~-:~
=8~ H
H 5
~
..
H
H~---
'
CH20H CH20H CH20H
e. Ollgosacchartdes: These carbohydrates yield two to ten confirms presence of five OH groups 8
a-D-(+)-glucose p.D-(+)-glucose
monosaocharide units on hydrolysis. They are further CHO CHO O
clasSified as disaccharides, trisaccharides etc. (ttiOH)4 Aceti~
~hyd~e I
(6HO - 8-
CH3 ) 4 o a and p forms of glucose are called anomers. Six
c. Polysaccharides: They yield a large number of I 0 membered cyclic structure of glucose is called pyranose
monosaccharide units on hydrolysis. CH2 0H . CH 0 CH3
2
-8·- structure
Example: Starch, Cellulose etc. o Glucose and gluconic acid is oxidised to saccharic acid
Monosaccharides: by nitric acid. This indicates presence of primary -OH
group
0 If a monosaccharide contains an aldehyde group, it is
knoWn as an aldose and if contains a keto group, it is CHO COOH COOH
I I
called ketose (tHOH) Oxidation (CHOH) Oxidation (CHOH)4
4 4
• I I I
(a) Glucose: It is an aldohexose· CH20H COOH CH20H OH
H OH H
Saccharic acid Gluconic
Structure of glucose acid a-D-(+)-Glucopyranose p.D-(+) -Glucopyranose
Glucose has been assigned the structure
o Fischer suggested following configuration of D(+) (b) Fructose
CHO
I glucose CHO o Fructose is a ketohexose
(CHOH)4 on the basis of following evidences:
H~i~O . o Following structures have been assigned to this molecule
u
I
CH20H 1 CH 0H
H OH 2 e 1 e
H OH I HOH2C O CH2 0H HOH2~ C H
o Its molecular formula is found to be C8_H 120a.
5 2 5 2
2C=O
$
o On prolonged heating with HI, it forms n-hexane, HO H H HO H HO
CH2_0 H H 4
OH H OH H CH2 0H
suggesting carbons are linked in straight chain. H s OH
4
J • 4 3 1
Cyclic Structure of Glucose
o Presence of carbonyl group is con_ firmed by the following
o The given observations could not explain chain structure 8
CH20H OH H OH H -
reactions. ~(-}-fructose a-~(-}-Fructofuranose ~0-(-}-Fructofuranose
ofglucose
,;CN (i) It does not react with NaHS03 or Schiff's reagent '
CH Tests of Glucose and Fructose
CH=N-OH
I 'OH
HCN
CHO
I
(ii) Pentaacetate of glucose does not react with NH20H.
Both _glucose and fructose reduce Tollen's reagent and
(CHOH)4 (CHOH)_. NH20H • (tHOH)_. (iii)Glucose exist in two different crystalline forms, a and p
I I I Fehling's solution. They are also called reducing sugars.
CH20H CH20H forms.
CH20H
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