Enzymes

Most enzymes are globular proteins

Active site: the region of an enzyme surface to which a specific set of substrates binds. Substrate: ( the reactant ) a molecule upon which an enzyme acts. A substrate molecule must fit precisely into an active site.

Cells employ enzymes to lower activation energies By bringing two substrates together in the correct orientation, or by stressing particular chemical bonds of a substrate, an enzyme lowers the activation energy required for new bonds to form.

Enzymes speed up the rate of chemical reactions Let us consider this reaction: CO2 + H2O H2CO3 carbon dioxide + water carbonic acid The reaction is very slow in the absence of an enzyme called carbonic anhydrase. Perhaps 200 molecules of carbonic acid are formed in an hour in a cell.

Under the same conditions, but with the presence of carbonic anhydrase, an estimated 600,000 molecules of carbonic acid form every second, thus the enzyme increases the reaction rate by more than 10 million times.

Enzymes are not consumed in the chemical reactions Because the enzyme itself is not changed or consumed in the reaction, only a small amount is needed, and it can be used over and over.

How Enzymes Work

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Enzymes are specific in their choice of substrate This specificity is due to the active site of the enzyme, which is shaped so that only a certain substrate will fit into it. Enzymes typically catalyze only one or a few chemical reactions.

Factors Affecting Enzyme Activity Temperature: Most human enzymes have temperature optima between 35 C and 40 C. pH: Most enzymes have a pH optimum; it usually lies in the range of pH 6 to 8.

Cofactors and Coenzymes The activity of enzymes is often facilitated by cofactors, which can be metal ions or other substances. Cofactors that are nonprotein organic molecules are called coenzymes