Carbohydrates

  • Organic compounds containing carbon, hydrogen and oxygen 
  • Made of a chain of monomers
  • Polymers are longer chains of repeating monomer units 
  • Basic monomer unit is called a monosaccharide
  • Two monosaccharides combine to for a disaccharide
  • Many monosaccharides combine to form a polysaccharide
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Monosaccharides

  • 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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Disaccharides

  • 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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Polysaccharides

  • 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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