Biology - Carbohydrates

Monosaccarides, Polysaccharides and Disaccharides.

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Function of carbohydrates:

1) Glucose produces energy in the cell for respiration

2) Starchs (plants) and glycogen (animals) provide a store of energy. Insoluble therefore osmitically inactive. Easily hydrolised to yield energy. Compact does not take up too much space.

3) Provides a carbon skeleton for the synthesis of other molecules.

4) Cellulose provides support, by giving strength to plant cell walls making them rigid and preventing the cell bursting.

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Triose C=3 C3H6O3 Examples: Intermediate in photosynthesis and respiration.

Petose C=5 C5H105 Examples: Ribose, Deoxyribose and ATP.

Hexose C=6 C6H12O6 Examples: Glucose - energy in respiration. Fructose - found in milk. (Reducing Sugar)

These exist as isomers i.e. same formulas, different structures.

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Maltose: Found in germinating cereals. Glucose + Fructose (Reducing Sugar)

Sucrose: Found in plants, Sugar cane and Sugar Beet. Glucose + Fractose (Non Reducing Sugar).

Lactose: Found in mammalian milk Glucose + Galactose (Reducing Sugar)

Test for reducing sugars: hydrolised by heating with dilute Hcl, neutralises with Sodium Hydrogen Carbonate, then heat with benedicts so the colour goes from blue to orange.

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Storage Hexosan e.g. Starch and Glycogen

Structural Hexosan e.g. Cellulose

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It's a mixture of two polysaccharides: Amylose and Amylopectin.

Amylose is not branched. It's a helix held in place by Hydrogen bonds.

Amylopectin is branched and shape is maintained by Hydrogen bonds.

Both are spiral and compact molecules, insoluble, ideal storage molecules and osmotically intact.

Glycogen in animals only has similar structure to starch, but is more branched.

Test for Starch: Iodine changes colour from brown to dark blue in the presence of starch.

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Unlike Starch it is very strong.

Beta glucose molecules linked by Beta 1-4 glycosidic links.

Everyalternate glucose unit rotates/ flips 180 degrees.

As a reult cell wall has TENSIBLE strength to support the cell and to stop it bursting when it swells. Cell wall is freely permeable.

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