Energy Flow in Cells - 9 Regulating Metabolism – Activation Energy, Catalysts and Enzymes We need to be able to control the chemical reactions that occur in our cells and tissues, and we need to be able to do the chemical reactions of metabolism within the temperature, pressure and concentrations of molecules that are found within our cells. Many of our metabolic reactions occur in pathways that must be tightly regulated or our cells cannot function. Much regulation of metabolism depends on the use of catalysts, substances that affect the rate of reactions. Catalysts An alternative to increasing the heat energy needed to activate a chemical reaction is to stress the bonds of the reactants to make them easier to break. Substances that can do this are called catalysts. A catalyst affects the bonds of the reactants in a way to reduce the activation energy needed to break the bonds, thus facilitating the rate of the chemical reaction. Characteristics
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