AS Biology Enzymes

Globular proteins that act as biological catalysts.

• Either a single molecule with a complementary shape or more than one molecule that joins together to make a complementary shape, can fit into the active site. These substrate molecules form temporary bonds with the amino of the active site to produce an enzyme substrate complex. When the reaction has taken place, the products are released, leaving the enzyme unchanged.

It has been found that the active site is often flexible. when the substrate enters the active site, the enzyme molecule changes shape slightly, fitting more closely around the substrate. Only a specific substrate will induce the changes in shape of an enzymes active site.

The energy needed to break bonds and start a reaction.

The specific shape of the enzymes active site and of the complementary substrate is such that electrically charged groups on their surfaces interact. The attraction of the oppositely charged groups may distort the shape of the substrate and assist in the breaking of bonds or in formation of new bonds. In some cases the active site may contain amino acids with acidic side chains; the acidic environment created within the active site may provide conditions favourable for the reaction