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Starch, Glycogen & Cellulose
[email protected]…read more

Slide 2

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· Plants store sugars for later use in the form of storage
polysaccharides ­ Starch ­ in seeds & storage organs (potato
· An important component of food & a major energy source
· Made up of chains of -glucose monomers linked by glycosidic
bonds that are formed by condensation reactions.
· The unbranched chain is wound into a coil (helix) making it
· Stains deep blue with iodine solution.…read more

Slide 3

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The main role of starch is energy storage, something it is specially
suited for because:
· being insoluble, it does not tend to draw H2O into cells by
· it also does not easily diffuse out of the cells.
· being compact, a lot of it can be stored in a small space.
· when hydrolyzed it forms -glucose, which is both easily
transported & readily used in respiration.
· Starch is never found in animal cells. Instead a similar
polysaccharide, called glycogen, serves the same role.…read more

Slide 4

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· Very similar in structure to starch ­ but has shorter chains and is
more highly branched.
· Major storage polysaccharide in animal cells ­ Animal starch
· Stored as small granules mainly in muscles and liver.
· More readily hydrolyzed to -glucose (because of smaller chains).
· Glycogen is found in animal cells but never in plant cells.…read more

Slide 5

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· Made of monomers of -glucose rather than -glucose.
· In the -glucose units, the positions of the ­H group and the ­OH
group on a single carbon atom are reversed.
· The ­OH group is above, rather than below, in -glucose.
· This means that to form a glycosidic links, each -glucose
molecules must be rotated by 1800.
· The result is that the ­CH2OH group on each alternates between
being above and below the chain.…read more

Slide 6

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Cellulose molecules are grouped together to form microfibrils
which are arranged in parallel groups called fibres.…read more

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