2-4 Chemical Reactions and Enzymes Metabolism: All living need to carry out chemical reactions in order to stay alive. Energy is released or absorbed whenever chemical bonds are formed or broken in a chemical reaction. • Exergonic Reaction: any chemical reaction that releases energy. – Sometimes occur spontaneously – Sometimes energy is needed to start an exergonic reaction. – Activation Energy: the energy needed to get a chemical reaction started. 2-4 Chemical Reactions and Enzymes Examples of exergonic reactions 2-4 Chemical Reactions and Enzymes 2-4 Chemical Reactions and Enzymes • Many of the chemical reactions • Enzymes: proteins that speed up the in cells have activation energy chemical reactions of that is too high and occur to cells. slow in order for the cell to (Enzymes are survive. biological catalysts) • To overcome this problem cells make catalysts: a substance that speeds up the rate of a chemical reaction by lowering the activation energy. 2-4 Chemical Reactions and Enzymes • Explain how the enzyme affects the chemical reaction. • Does the enzyme have any affect on the product of the reactants?