Enzymes are special proteins that cause reactions to happen in the body without raising the temperature. they are considered organic catalysts. since they are proteins, their are made of chains of amino acids which in turn are controlled by sequences of DNA called genes located on chromosomes. Each enzyme is specific for one reaction. Each enzyme has a specific active site which binds to a specific substrate (substance in the environment). If this binding does not occur, the enzyme will not function. Enzymes can break down large molecules (as in digestion) or they can build up small molecules into larger ones (as in assimilation of body parts from the raw materials). Since enzymes are proteins, they have a specific 3-D structure. Since they are made of amino acids, each amino acid consists of a central Carbon atom with a hydrogen attached, as well as an amino group and a carboxyl group and one different group called the "R" group.