Lock-and-key model (enzyme)

The lock and key structure in biochemistry is a theory on why enzymes catalyse reactions. This theory states that all enzymes and substrates (the object which the enzyme act on) have specified structures (active site) and chemical properties. The substrate fits into the enzyme's active site, and they react. The substrate is broken down, and then the enzyme can act on the next substrate. This can be done as quickly as 32 million particles per second. The induced fit model is an expansion.

This means that, like only a certain and correctly sized and shaped key can fit into a certain lock, only a certain substrate (key) can fit into a certain active site (or key hole) in the enzyme(lock). This model was replaced with the latter induced fit model, in this model the enzyme changes shape in the active site to adapt to the form of the substrate.

Part of this is the idea of competitive inhibition, where an inhibitor competes with the substrate for the active site. Non-competitive inhibition is a form of inhibition, where the inhibitor binds to an allosteric site of an enzyme which is not near the active site. The binding of the inhibitor to the allosteric site results in the alterations in the shape of the enzyme, resulting in a distorted active site that does not function properly.

The binding of a non-competitive inhibitor is usually temporary. Poisons are inhibitors that bind irreversibly. For example, penicillin inhibits an enzyme needed by bacteria to build the cell wall.

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