Enzymes are proteins, and their functions are determined by their complex structure. The way enzymes work can also be shown by considering the energy changes that take place during a chemical reaction. We shall consider a reaction where the product has a lower energy than the substrate, so the substrate naturally turns into product (in other words the equilibrium lies in the direction of the product). Before it can change into product, the substrate must overcome an ‘energy barrier’ called the activation energy (EA). The larger the activation energy, the slower the reaction will be because only a few substrate molecules will by chance have sufficient energy to overcome the activation energy barrier.
How do enzymes affect the activation energy of the reactants?

(A) They lower the overall activation energy of reactants.


From the curve it is shown that the enzymes lower the activation energy of the reactants.

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