Chapter 6 - Enzymes and Enzyme Regulation

Abstract

Chemical reactions within cells and tissues that are thermodynamically favorable and thus occur without input of energy from other sources may occur too slowly to be useful to a living organism. Similarly, reactions that can occur are unlikely to be those needed by the organism. Enzymes both guide the chemical reactions within an organism and determine the speed at which the reactions occur. Guidance is achieved by making biochemical reactions and pathways more favorable by coupling reactions together; speed is determined by the concentrations of the chemical reactants and the ability of the enzyme to reduce the activation energy required for transforming one substance (substrate) into another (product). Which substance is transformed and the product of the transformation is the result of the structure of the active site of an enzyme and the participation of cofactors that participate with the enzyme in the chemical reaction. Sites on enzymes different from the active site, regulatory (allosteric) sites, bind other molecules to regulate the efficiency of the enzyme in catalyzing its specific biochemical reaction. Substances similar and dissimilar in structure to an enzyme’s substrate can inhibit the enzyme and act to control the enzyme’s activity and throughput in a biochemical pathway.