Cracking the AP Biology Exam

4

Cellular Energetics

ENZYMES

Most chemical reactions do not occur haphazardly in the cell. To help control the chemical reactions essential for life, cells rely on enzymes. These proteins help “kick-start” reactions and speed them up once they get rolling, enabling cells to get the most out of the energy sources available to them. Officially, this boils down to the following definition:

Enzymes are organic catalysts; they speed up the rate of a reaction without altering the reaction itself.

That is, they catalyze them without being changed in the reaction themselves. Before we discuss precisely how this works, let’s review some of the different types of reactions that can occur within a cell.