This document discusses the classification and structure of carbohydrates. It defines carbohydrates as polyhydroxyaldehydes or polyhydroxyketones with the formula (CH2O)n. Carbohydrates are classified as monosaccharides, disaccharides, oligosaccharides, or polysaccharides depending on the number of monosaccharide units they contain. Examples like glucose, fructose, maltose, sucrose, starch, glycogen and cellulose are provided along with their structures. Reducing and non-reducing sugars are also defined.

2.  To learn,
1. Definition and classification of carbohydrates
2. Monosaccharides: examples with structure
3. Disaccharides: examples with structure
4. Polysaccharides: examples with structure
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3.  Carbohydrates – polyhydroxyaldehydes or
polyhydroxy-ketones of formula (CH2O)n, or
compounds that can be hydrolyzed to them.
 They are classified as
 Monosaccharide (Monomers): carbohydrates that
cannot be hydrolyzed to simpler carbohydrates; eg.
Glucose or fructose.
 Disaccharides (Dimers): carbohydrates that can be
hydrolyzed into two monosaccharide units; eg.
Sucrose, maltose
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4.  Oligosaccharides – carbohydrates that can be
hydrolyzed into a few monosaccharide units.alose
e.g. raffinose, stachyose
 Polysaccharides – carbohydrates that are are
polymeric sugars; eg Starch , cellulose.
 Homopolysaccharides: made up of number of
single monosaccharide units e.g. starch, cellulose
 Heteropolysaccharides: made up of more than one
type of monosaccharide units e.g. agar, pectin,
muccopolysaccharides
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5.  Aldose – polyhydroxyaldehyde, eg glucose
 Ketose – polyhydroxyketone, eg fructose
 Reducing sugar – a carbohydrate that is oxidized by
Tollen’s, Fehling’s or Benedict’s solution.
 Tollen’s: Ag+  Ag (silver mirror)
 Fehling’s or Benedict’s: Cu3+ (blue)  Cu2+ (red ppt)
 These are reactions of aldehydes and alpha-
hydroxyketones.
 All monosaccharides (both aldoses and ketoses) and
most* disaccharides are reducing sugars.
 Sucrose, is not a reducing sugar.
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6.  Glucose is the most important monosaccharide.
C
C OH
H
C H
HO
C OH
H
C OH
H
CH2OH
D-glucose
O
H
C H
HO
C OH
H
C OH
H
CH2OH
CH2OH
C O
D-fructose
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7.  D & L designations are based on the configuration about the
single asymmetric C in glyceraldehyde.
 For sugars with more than one chiral center, D or L refers to
the asymmetric C farthest from the aldehyde or keto group.
CHO
C
CH2OH
HO H
CHO
C
CH2OH
H OH
CHO
C
CH2OH
HO H
CHO
C
CH2OH
H OH
L-glyceraldehyde
D-glyceraldehyde
L-glyceraldehyde
D-glyceraldehyde
O H O H
C C
H – C – OH HO – C – H
HO – C – H H – C – OH
H – C – OH HO – C – H
H – C – OH HO – C – H
CH2OH CH2OH
D-glucose L-glucose
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8.  Disaccharides are carbohydrates which on hydrolysis
give two molecules of monosaccharides.
 Maltose-It is a cleavage product of starch, is a
disaccharide with α (1 4) glycosidic linkage
between C1 - C4 OH of 2 glucoses. It is a reducing
sugar.
H O
OH
H
OH
H
OH
CH2OH
H
O H
OH
H
OH
H
OH
CH2OH
H
O
H
H
1
2
3
5
4
6
1
2
3
4
5
6
maltose
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9.  Sucrose- Is a common table sugar, has a glycosidic
bond linking the anomeric hydroxyls of glucose &
fructose with the linkage is α (12). The full name of
sucrose is a-D-glucopyranosyl-(12)-b-D-
fructopyranose. It is a non reducing sugar.
 Lactose- Is a milk sugar, is composed of galactose &
glucose, with β (14) linkage from the anomeric OH
of galactose. Its full name is b-D-galactopyranosyl-(1
4)-a-D-glucopyranose. It is a reducing sugar.
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10.  Polysaccharides: Carbohydrates which on hydrolysis
give more than ten monosaccharide units are called as
polysaccharides.
 Polysaccharides are classified as;
 Homopolysaccharides: Polysaccharides which on
hydrolysis give number of units of same
monosaccharide. E.g. Starch, Glycogen, Cellulose etc.
 Heteropolysaccharides: Polysaccharides which on
hydrolysis give number of units of more than one
monosaccharide. E.g. heparin, agar, gum etc.
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11. H O
OH
H
OH
H
OH
CH2OH
H
O H
H
OH
H
OH
CH2OH
H
O
H
H H O
O
H
OH
H
OH
CH2OH
H
H H O
H
OH
H
OH
CH2OH
H
OH
H
H O
O
H
OH
H
OH
CH2OH
H
O
H
1
6
5
4
3
1
2
amylose
H O
OH
H
OH
H
OH
CH2OH
H
O H
H
OH
H
OH
CH2OH
H
O
H
H H O
O
H
OH
H
OH
CH2
H
H H O
H
OH
H
OH
CH2OH
H
OH
H
H O
O
H
OH
H
OH
CH2OH
H
O
H
O
1 4
6
H O
H
OH
H
OH
CH2OH
H
H H O
H
OH
H
OH
CH2OH
H
H
O
1
OH
3
4
5
2
amylopectin
Starch: It is made up of two units- Amylose and amylopectin.
Starch is storage of glucose in plants. Amylose is a glucose
polymer with α (14) linkages. Amylopectin is a glucose
polymer with mainly α (14) linkages, but it also has
branches formed by α (16) linkages.
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12. cellulose
H O
OH
H
OH
H
OH
CH2OH
H
O
H
OH
H
OH
CH2OH
H
O
H H O
O H
OH
H
OH
CH2OH
H
H O
H
OH
H
OH
CH2OH
H
H
OH
H O
O H
OH
H
OH
CH2OH
H
O
H H H H
1
6
5
4
3
1
2
Glycogen- the glucose storage polymer in animals is similar in
structure to amylopectin.
But glycogen has more α(16) branches.
The highly branched structure permits rapid glucose release
from glycogen stores, e.g., in muscle during exercise.
Cellulose- a major constituent of plant cell walls, consists of
long linear chains of glucose with β(14) linkages
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13. “In a day, when you don't come
across any problems - you can be
sure that you are travelling in a
wrong path”.
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