Starch, Glycogen & Cellulose

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Ellianna Gibbs L6.03
Starch, Glycogen and Cellulose
Starch
A polysaccharide found in parts of a plant in the form of small grains.
It forms a large component of food and is the energy source in most diets. Starch is made
up of chains of -glucose monosaccharides linked by glycosidic bonds formed by
condensation reactions.
The unbranched chain is wound into a tight coil that makes the molecule very compact.
Starch is suited for energy storage because:
It's insoluble and doesn't draw water into cells.
It doesn't easily diffuse out of cells.
It's compact so a lot can be stored in a small space.
When hydrolysed it forms -glucose which is easily transported and readily used in transpiration.
Glycogen
This is similar to starch but has shorter chains and is more highly branched in animals it is
stored as small granules mainly in the muscles and liver.
Cellulose
This differs from starch and glycogen as it's made of monomers and -glucose. The main
reasons for difference in the structure and function is that in the -glucose units the
position of the ­H and the ­OH group are reversed. In the -glucose the ­OH group is
above the ring.
Cellulose has straight unbranched chains that run parallel to one another; following
hydrogen bonds to form cross-linkages between adjacent chains.
The cellulose molecules are grouped to form microfibrils which are arranged in parallel
groups called fibres.
Cellulose is a major component of plant cell walls and provides rigidity. The wall also
prevents the cell from bursting as water enters by osmosis. IT exerts an inward pressure
that stops further influx of water.
-glucose is linked by glycosidic bonds formed by condensation to form
cellulose.

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