How is an enzyme specific for a particular type of molecule?

Enzymes are protein molecules responsible for the catalysis-the increase in the rate of a reaction- of reactions taking place within our body. They are able to catalyse many reactions by their high specificity for substrates. They get this high specficity from their active site. The active site varies in shape and size between enzymes. Substrates fit into these sites of the enzymes like a key fits into a lock. The most important key note to take from this then is that enzymes are specific for substrates based on their active site which ensures only the correct substrate can enter for a reaction to take place.  The key points: 1. Enzymes are not free to react with all substrates available in the vicinity of it.  2. They are specfic to subtrates through their active site 3. The active site is a region on the enzyme which varies between enzymes making them specific for certain substrates and reactions 4. These active sites differ from one another by size and shape 5. Only the correct substrate will enter the active site 6. This can be sumarised as a substrate acting as a key to the active site i.e. the lock