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Cytology

Lactose (milk sugar) during lactation. It is derived from the
This is found exclusively in the milk condensation of galactose and glucose
of mammals and in the milk products. linked by 1, 4 - glycosidic bond (Figure
Lactose is the only carbohydrate of milk 1.23).
which is synthesised by mammary glands

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Figure 1.23: Chemical combination between galactose and glucose to form lactose
Figure 1.24 Chemical combination between galactose and glucose to form lactose
Polysaccharides (multi-sugars) monosaccharides, linked together by
Polysaccharides are polymer carbohydrate glycosidic bonds. They are large molecules
molecules, composed of long chains of which are often insoluble in water and exist
monosaccharide units bound together by in non-crystalline form.
glycosidic bonds. On hydrolysis, they
give their constituent monosaccharides. Starch
They range in structure, from linear to Starch is a polymer of hexose sugar (α
highly branched molecules. Examples glucose) that can be extracted as a white
of polysaccharides include storage powder. It is a major storage carbohydrate of
polysaccharides such as starch and glycogen plants, and it is a product of photosynthesis.
as well as structural polysaccharides such Chemically, starch is a polymer of repeated
as cellulose and chitin. Starch is the main a-glucose units that are bonded together
storage form of polysaccharides in plants. by glycosidic bonds. This polysaccharide
It is made up of two polymers, amylose is a mixture of two substances; amylose
and amylopectin while in animals and and amylopectin. Amylose unit is a linear,

fungi, glycogen is the main storage form helical chain which consists of around 500
of polysaccharides. In plants, cellulose is to 20,000 monosaccharides connected by a
a structural constituent of their cell walls (1-4) glycosidic bonds between the glucose
while in fungi and most arthropods, chitin units. Amylopectin differs from amylose in
is the structural constituent of the cell wall being highly branched, and has short side
and exoskeleton, respectively. chains of about 30 glucose units, linked
with α (1-6) glycosidic bonds in addition
Properties of polysaccharides to 1,4-glycosidic bonds (Figure 1.24).
Polysaccharides are complex carbohydrate Amylopectin molecules may contain up
polymers, consisting of several to two million glucose units.

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