Enzymes review

Enzyme

A biological catalyst (usually a protein)

Catalyst

A substance that speeds up a chemical reaction without being changed

Factors affecting enzyme activity

Enzyme activity can be affected by a variety of factors, such as temperature, pH, and concentration. Enzymes work best within specific temperature and pH ranges, and sub-optimal conditions can cause an enzyme to lose its ability to bind to a substrate. Temperature: Raising temperature generally speeds up a reaction, and lowering temperature slows down a reaction. However, extreme high temperatures can cause an enzyme to lose its shape (denature) and stop working. pH: Each enzyme has an optimum pH range. Changing the pH outside of this range will slow enzyme activity. Extreme pH values can cause enzymes to denature. Enzyme concentration: Increasing enzyme concentration will speed up the reaction, as long as there is substrate available to bind to. Once all of the substrate is bound, the reaction will no longer speed up, since there will be nothing for additional enzymes to bind to. Substrate concentration: Increasing substrate concentration also increases the rate of reaction to a certain point. Once all of the enzymes have bound, any substrate increase will have no effect on the rate of reaction, as the available enzymes will be saturated and working at their maximum rate.

Common mistakes and misconceptions

Enzymes are "specific." Each type of enzyme typically only reacts with one, or a couple, of substrates. Some enzymes are more specific than others and will only accept one particular substrate. Other enzymes can act on a range of molecules, as long as they contain the type of bond or chemical group that the enzyme targets. Enzymes are reusable. Enzymes are not reactants and are not used up during the reaction. Once an enzyme binds to a substrate and catalyzes the reaction, the enzyme is released, unchanged, and can be used for another reaction. This means that for each reaction, there does not need to be a 1:1 ratio between enzyme and substrate molecules.

Enzyme structure and function

Enzymes are catalysts. They are usually proteins, though some RNA molecules act as enzymes too. Enzymes lower the activation energy of a reaction - that is the required amount of energy needed for a reaction to occur. They do this by binding to a substrate and holding it in a way that allows the reaction to happen more efficiently. The part of the enzyme where the substrate binds is called the active site. Here, the enzyme changes shape slightly, fitting tightly with the substrate and forming the enzyme/substrate complex.

Active site

The part of the enzyme where the substrate binds

Substrate

The reactant molecule that an enzyme works on