Starch, glycogen and cellulose

Cellulose
1. Made from monomers of beta glucose
  1. In Beta glucose, the OH group is above rather than below the ring
  2. Therefore to form glycosidic bonds, each molecule must be rotated by 180 degrees
2. It therefore forms straight, unbranched chains
3. Chains run parallel to one another, allowing hydrogenn 'bonds' to form cross-linkages between adjacent chains
4. Sheer overall number of hydrogen bonds gives cellulose considerable strength
5. Cellulose are grouped togethwe to form microfibrils
6. Microfibrils are arranged in parallel groups called fibres
7. In cell walls it exerts an inward pressure to prevent cells bursting, and this stops more water entering the cell
Starch
1. Main role of starch is energy storage
2. Suited to function
  1. Insoluable so doesnt draw water into the cells by osmosis
  2. Insoluable so doesnt easily diffuse out of cells
  3. Compact, so lots of it can be stored in a small place
  4. When hydrolysed it forms alpha glucose which is easily transported and readily used in respiration
3. Never found in animal cells - glycogen is used
4. Found in many parts of a plant in the form of small grains
5. Large amounts occur in seeds and storage organs, such as potato tubers
6. Important food component and major energy source in most diets
7. Chains of alpha glucose monosaccharides linkied by glycosidic bonds
8. Unbranched chain is wound into a tight coil making the molecule compact
Glycogen
1. Similar structure to starch
  1. Has shorter chains
  2. More highly branched
2. Major carbohydrate storage product of animals
3. Stored as small granuals mainly in the muscles and the liver
4. Suited for storage in the same way starch is
5. As it is made up of smaller chains, it is even more readily hydrolysed
6. Found in animals, but never plants

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Starch, glycogen and cellulose

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	Created by Beth Ritchie about 10 years ago