C.7.4

Describe the concept of the active site in enzyme structure.
The action of an enzyme is specific. This means that a particular enzyme can only catalyze one particular reaction.

The active site is the part of an enzyme (E) that reacts with the substrate (S). The active site is the place on the enzyme where the substrate (reactant/s) reacts to form products. The product then leaves the enzyme.

Step 1: Enzyme reacts with the substrate at the active site E + S --» ES Step 2: After the reaction has occured the product leaves the enzyme EP ---» E + P

The enzyme if a **biological catalyst**. The active site where the substrate binds provides an alternative pathways for the reaction that has a lower activation energy.

In lock and key model, the shape of active site is fixed so that only a particular substrate can fit, and hence react.
 * __Lock and Key model__**

The active site does not necessarily have a fixed and rigid shape, but can change its shape to allow for a better fit between substrate and enzyme. This increase the surface area between the substrate and enzyme.
 * __Induced fit model__**

http://ghs.gresham.k12.or.us/science/ps/sci/ibbio/chem/notes/chpt8/activesite.gif