Carbohydrates

AS Biology

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Starch

Starch is the storage of energy in plants and is made up of 2 polymers/polysaccharides of alpha-glucose: Amylose and Amylopectin.
Amylose is a long, un-branched chain and has 1,4 glycosidic bonds. It has a coiled structure which makes it quite compact, which makes it really good for storage because it can be fit into a small space.
Amylopectin is a long, branched chain and has 1,4 and 1,6 glycosidic bonds. The side branches allow the enzymes to get at the glycosidic bonds easily, therefore the glucose can be released quickly.
Starch is insoluble in water, so it doesn't cause water to enter cells by osmosis. Which therefore makes it good for storage.

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Glycogen

Glycogen is the main energy storage in animals and fungi. Animal cells can get energy from glucose aswell, but the excess glucose is stored as glycogen.
It has a similar structure to amylopectin but glycogen has more and shorter side branches which means that the glucose stored can be released quickly.
It is a very compact molecule which makes it good for storage.
It is also insoluble in water, so cells don't swell due to osmosis.
It is a fairly large molecule, so lots of energy can be stored.
In humans, glycogen is stored in the liver and muscles.

Similarities between glycogen & amylopectin:
1. Consist of 1,4 & 1,6 Glycosidic bonds
2. Branched
3. Made of alpha-glucose molecules

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Cellulose

Cellulose is the constituent of cell walls. In the diet it is known as the dietary fibre, or as a non-starch polysaccharide. Up to 10,000 glucose molecules form a straight chain without branches.
It has a 1,4 glycosidic bond

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