Active Sites

Because of secondary and tertiary structures, proteins adopt specific shapes. The spot at which two molecules with specific shapes fit together to interact is called the active site. This active site is the basis of the lock and key model. The active site is called active because interaction of the molecules in this way usually results in some chemical change or reaction.

Below is a representation of a small molecule (green helix) interacting with a large molecule (gray globular shape with yellow, orange and red colors) in the active site. The colored regions indicate where the large molecule touches the small one.