Enzymes – speed up the rate of chemical reactions Substrates – molecules which react with enzymes Only one small part of an enzyme, called the active site, reacts with the substrate(s). Active site may undergo a slight change in shape in order to fit with the substrate The enzyme is not changed by the reaction (active site returns to its original state), and it is free to act again. E1 E2 E3 E4 E5 E6 A → B → C → D → E → F → G
