B2.5 Proteins - Their Functions And Uses

B2.5 Proteins - Their Functions And Uses

1. B2.5.1 Proteins

   • Proteins have many functions, both inside and outside the cells of living organisms. Proteins, as enzymes, are now used widely in the home and in industry.
     • Protein molecules are made up of long chains of amino acids. These long chains are folded to produce a specific shape that enables other molecules to fit into the protein. Proteins act as structural components of tissues such as muscles, hormones, antibodies and catalysts.
       • Catalysts increase the rate of chemical reactions. Biological catalysts are called enzymes. Enzymes are proteins.

2. B2.5.2 Enzymes

   • The shape of an enzyme is vital for the enzyme's function. High temperatures change the shape.
     • Different enzymes work best at different pH values.
       • Some enzymes work outside the body cells. The digestive enzymes are produced by specialised cells in glands and in the lining of the gut. The enzymes then pass out of the cells into the gut where they come into contact with food molecules. They catalyse the breakdown of large molecules into smaller molecules.
         • The enzyme amylase is produced in the salivary glands, the pancreas and the small intestine. This enzyme catalyses the breakdown of starch into sugars in the mouth and small intestine.
           • Protease enzymes are produced by the stomach, the pancreas and the small intestine. These enzymes catalyse the breakdown of proteins into amino acids in the stomach and the small intestine.
             • Lipase enzymes are produced by the pancreas and small intestine. These enzymes catalyse the breakdown of lipids (fats and oils) into fatty acids and glycerol in the small intestine.
               • The stomach also produces hydrochloric acid. The enzymes in the stomach work most effectively in these acid conditions.
                 • The liver produces bile, which is stored in the gall bladder before being released into the small intestine. Bile neutralises the acid that was added to food in the stomach. This provides alkaline conditions in which enzymes in the small intestine work most effectively.
                   • Some microorganisms produce enzymes that pass out of the cells. These enzymes have many uses in the home and in industry.
                     • At home, biological detergents may contain protein-digesting and fat-digesting enzymes (proteases and lipases) and these detergents are more effective at low temperatures than other types of detergents.
                       • In industry, proteases are used to 'pre-digest' the protein in some baby foods, carbohydrases are used to convert starch into sugar syrup and isomerase is used to convert glucose syrup into fructose syrup, which is much sweeter and therefore can be used in smaller quantities in slimming foods.
                         • In industry, enzymes are used to bring about reactions at normal temperatures and pressures that would otherwise require expensive, energy-demanding equipment. However, most enzymes are denatured at high temperatures and many are costly to produce.