A substrate is a molecule acted upon by an enzyme. A substrate is loaded into the active site of the enzyme, or the place that allows weak bonds to be formed between the two molecules. Substrate may also refer to the surface on which an organism moves. The substrate is changed by the reaction and, in this case, two products are made. A reactant and substrate have the same meaning (see: Wikipedia). For example, Glucose and glycogen are the substrates for aerobic and anaerobic glycolysis.