Enzymes are proteins .
Like other proteins, enzymes consist of long chains of amino acids held together by peptide bonds. They are present in all living cells, where they perform a vital function by controlling the metabolic processes whereby nutrients are converted into energy and fresh cell material. Furthermore, enzymes take part in the breakdown of food materials into simpler compounds. Some of the best known enzymes are those found in the digestive tract where pepsin, trypsin and peptidases break down proteins into amino acids, lipases split fats into glycerol and fatty acids, and amylases break down starch into simple sugars. Enzymes are catalysts Enzymes are capable of performing these tasks because, unlike food proteins such ascase in egg albumin, gelatine or soya protein, they are catalysts.