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Enzymes and Activation Energy • The diagram, to the right, shows hypothetical relationships between temperature and enzyme activity for a human and for a thermophilic (heat loving) bacteria. • Notice the optimum (best) activity level for each enzyme matches the environment that the enzyme has to work in. • Human enzymes generally work best at our temperature (37°C) while the thermophilic bacteria's enzyme works best at a higher temperature. • Indeed some of these thermophilic organisms live quite nicely at the boiling point of water. • Enzymes and activation energy • All chemical reactions require some amount of energy to get them started. • This energy is called activation energy. • The way enzymes operate is by effectively lowering the amount of activation energy required for a chemical reaction to start. • Sometimes this happens because enzymes might weaken a covalent bond within a substrate molecule. • In other cases this lowering of activation energy seems to happen because the enzyme holds the substrate molecules in a particular position that increases the likely that the molecules are going to react. • Energy hill diagrams are a good way to visualize the effect of enzymes on activation energy. • The diagram shows time on the horizontal (side-to-side) axis and the amount of energy in the chemicals involved in a chemical reaction on the vertical (up-and-down) axis. • The point if this diagram again is that without the enzyme, much more activation energy is required to get a chemical reaction to take place. kMc/ym 07 http://staff.jccc.net/pdecell/metabolism/enzymes/enzymes.html