- Relatively small organic molecules
- Provide the building blocks for larger carbohydrates
- General formula = (CH20)n
- Name determined by the number of carbon atoms in the molecule
- All hexose sugars have the formula C6H1206 but differ in their molecular structure
- Usually exist as a ring of structures when dissolved in water
- Glucose exists as two isomers - alpha and beta form which result in considerable biological differences when they form polymers e.g. starch and cellulose
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- Consist of two monosaccharide units linked with the formation of a glycosidic bond and the elimination of water (condenstaion reaction)
- Formed by the joining of two similar of different monosaccharides
- Glucose + glucose = maltose
- Glucose + fructose = sucrose
- Glucose + galactose = lactose
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- Example of large, complex molecules (polymers)
- Formed from large numbers of monosaccharide units linked together by glycosidic bonds
- Starch - storage polysaccharide found in plants cells in the form of starch grains. Found in seeds and storage organs, e.g. potato tubers. Made up alpha-glucose molecules. Ideal storage molecule because it's compact. Insoluble and does not draw water by osmosis.
- Starch - made up of amylose and amylopectin. Amylose is unbranched and cols into a helix. Amylopectin is branched and fits inside amylose.
- Glycogen = main storage product in animals
- Starch and glycogen are readily hydrolysed to alpha-glucose which is insoluble and can then be transported to areas where energy is needed
- Cellulose = structural polysaccharide. Major component of plant cell walls
- Cellulose - many long parallel chains of beta-glucose cross-linked by H-bonds . Chain has adjacent glucose molecules rotated by 180 degrees allowing H-bonds to be formed between hydroxyl groups of adjacent parallel chains giving cellulose is stability
- Chitin - polysaccharide found in insects. Similar to cellulose but has amino acids added to form a mucopolysaccharide. Strong, waterproof and ligtweight. Forms exoskeleton of insects.
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