1
Disaccharides with
examples
2
DISACCHARIDES
When two monosaccharides are combined together
by glycosidic linkage, a disaccharide is formed. The
important disaccharides are
1. Sucrose
2. Maltose and isomaltose
3. Lactose.
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A disaccharide
• consists of two monosaccharides linked together.
• is formed when two monosaccharides combine in a
dehydration reaction.
Monosaccharides
Disaccharide
glucose + glucose
maltose + H
2
O
glucose + galactose
lactose + H
2
O
glucose + fructose
sucrose + H
2
O
The most common disaccharides are maltose, lactose,
and sucrose.
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Glycoside formation
Glycoside formation
or -OH group of cyclic monosaccharide
can form link with another one (or more).
glycosidic bond
sugar -O- sugar
oxygen bridge
O
H
OH
OH
H
H
H
OH
CH
2
OH
H
O
H
OH
H
OH
H
OH
H
OH
CH
2
OH
H
OH
O
H
OH
H
H
H
OH
CH
2
OH
H
O
H
OH
H
H
OH
H
OH
CH
2
OH
H
OH
o
+ H
2
O
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Glycosidic bonds
Glycosidic bonds
O
O
Type is based on the position of the C-1 OH
glycosidic bond
- linkage between a C-1
OH and a C-4 OH
glycosidic bond
- linkage between a C-1
OH and a C-4 OH
bonds
bonds
O
O
C-4 end can be either up or down depending
on the orientation of the monosaccharide.
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Glycosidic bonds
Glycosidic bonds
General format used to describe bond.
OH type carbon# of carbon# of
(
or ) first sugar second sugar
As we work through the next few examples
this will become clear.
For disaccharides
- the sugar is either
or
based on form of the
remaining C-1 OH.
(
)
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-Maltose
-Maltose
Malt sugar.
Not common in nature except in
germinating grains.
-D-glucose
-D-glucose
O
H
OH
H
H
H
OH
CH2OH
H
OH
O
H
OH
H
H
H
OH
CH2OH
H
OH
O
-D-glucose and
-D-glucose, (1
4) linkage.
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-Maltose
-Maltose
It is referred to as
-maltose because the
unreacted C-1 on
-D-glucose is in the
position.
O
H
OH
H
H
H
OH
CH2OH
H
OH
O
H
OH
H
H
H
OH
CH2OH
H
OH
O
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-Maltose
-Maltose
Uses for
-maltose
Ingredient in infant formulas.
Production of beer.
Flavoring - fresh baked aroma.
It is hydrolyzed the in body by:
maltose + H
2
O 2 glucose
maltase
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Cellobiose
Cellobiose
Like maltose, it is composed of two molecules of
D-glucose - but with a
(1 4) linkage.
H
O
OH
H
OH
H
OH
CH
2
OH
H
H
O
H
O
H
OH
H
OH
CH
2
OH
H
H
OH
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Cellobiose
Cellobiose
O
H
OH
H
H
H
OH
CH 2 OH
H
OH
O
H
OH
H
H
H
OH
CH 2 OH
H
OH
O
H
O
OH
H
OH
H
OH
CH
2
OH
H
H
O
H
O
H
OH
H
OH
CH
2
OH
H
H
OH
The difference in
the linkage results
in cellobiose
being unusable
We lack an enzyme
that can hydrolyze
cellobiose.
cellobiose
(1 4)
maltose,
(1 4)
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Lactose
Lactose
Milk sugar
- dimer of
-D-galactose and
either the
or - D-glucose.
-Lactose
O
OH
H
H
H
H
OH
CH2OH
H
OH
O
H
OH
H
H
H
OH
CH2OH
H
OH
O
-D-galactose
-D-glucose
(1 4) linkage,
disaccharide.
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Lactose
Lactose
We can’t directly use galactose. It must be
converted to a form of glucose.
Galactosemia
- absence of needed enzymes
needed for conversion.
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Lactose
Lactose
Lactase
Enzyme required to hydrolyze lactose.
Lactose intolerance
Lack or insufficient amount of the
enzyme.
If lactase enters lower (GI)Gastro intestinal,
it can cause gas and cramps.
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Sucrose
Sucrose
Table sugar - most
common sugar in all
plants.
Sugar cane and beet,
are up to 20% by
mass sucrose.
Disaccharide of
-glucose and
-fructose.
(1 2) linkage
CH
2
OH O
CH
2
OH
H
OH
H
H
OH
H
O
OH
H
H
OH
H
OH
CH
2
OH
H
O