How Does An Enzyme Work?

Enzymes speed up reactions by lowering their activation energy, which is the energy required to jumpstart a chemical reaction. This enables the reactant molecules to reach the transition state quicker by absorbing enough energy to break their bonds and become unstable. Another name for the reactant molecules is substrates. Substrates are what the enzyme acts on, and they bind to the enzyme to form enzyme-substrate complexes. There is a restricted region on an enzyme molecule to which a substrate will bind and where catalysis occurs. This region, usually an indention or pocket, is called the active site. The active site is formed by some of the enzyme protein's amino acids, and has a particular configuration, which attributes to an enzyme's specificity. An enzyme must have a compatible fit between the shape of its active site and the shape of its substrate in order to carry out the chemical reaction. As temperature increases, the rate of an enzyme-catalyzed reaction increases as well. However, once the enzyme exceeds its optimal temperature, denaturing takes place, which means their protein structure breaks down and the enzyme is deactivated.

Just as an enzyme has an optimal temperature, it also has an optimal pH at which it is most active. There are a few exceptions, but pH values that optimize a majority of enzymatic activities fall in the range of pH 6-8, which is around neutral on the pH scale. A pH lower or higher than an enzyme's optimal pH results in denaturation of the protein.

As long as the reaction is not limited by substrate availability, increasing the amount of enzymes will sufficiently increase the rate at which substrates are converted to products. Similarly, adding substrates to the reaction when the enzyme concentration is kept constant also boosts the rate at which the enzyme works. However, there is a maximum to be reached. At the maximum, all enzymes become occupied by a substrate; therefore, increasing substrate concentration beyond maximum will no longer increase reaction rate.

For example, the substrates of the enzyme catecholase are oxygen and catechol, and the products formed by the reaction of these two reactants are benzoquinone and water. During the reaction, catechol is oxidized and oxygen is reduced. Benzoquinone molecules link together to form chains that create brown pigments, which is apparent when peeled fruits and vegetables turn brown when exposed to air.
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