A macromolecule, usually a protein, that serves as a biological catalyst, changing the rate of a chemical reaction without being consumed by the reaction Lowering the EA needed for a reaction to begin The specific reactant that an enzyme acts on A substrate fits into a region of the enzyme Many enzymes require nonprotein helpers A cofactor is an organic molecule A chemical that interferes with an enzyme’s activity by Block substrates from entering the active site Binds to the enzyme somewhere other than the active site, preventing the substrate from binding The product may act as an inhibitor of one of the enzymes in the pathway that produced it
