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Six facts about carbohydrates

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  • Carbohydrates contain carbon, oxygen and hydrogen.

  • Carbohydrate monomers are called monosaccharides e.g. glucose and fructose.

  • Two monomers are joined by a glycosidic bond to form a disaccharide e.g. sucrose.

  • Carbohydrate polymers e.g. starch, glycogen and cellulose are formed from many monomers joined by glycosidic bonds.

  • The bonds between the monomers in disaccharides and polysaccharides can be broken by hydrolysis .

  • Carbohydrates are important sources and stores of chemical energy. There are chemical tests to indicate if they are in food.

A condensation reaction forms a bond between a carbon atom from each sugar. A glycosidic bond is broken by the addition of water. Hydrolysis can be carried out by warming with an acid or by an enzyme. Reducing sugars (e.g. glucose) give a yellow or red colour change when heated with Benedicts reagent. Non-reducing sugars do not produce the colour change unless they are first hydrolysed with acid.