Enzymes and Metabolism

Metabolism is the sum of all the chemical reactions in a cell, and almost every one of those reactions is controlled by an enzyme. This lesson explains how enzymes work, what affects their activity, how they can be inhibited, and how metabolism harvests energy through cell respiration.

Enzymes as biological catalysts

Enzymes are biological catalysts, almost always proteins, that speed up chemical reactions without being used up. They work by lowering the activation energy, the energy barrier that must be overcome for a reaction to proceed. Each enzyme has a specific region called the active site whose shape is complementary to a particular substrate. When the substrate binds, it forms an enzyme–substrate complex. The older lock and key model pictured a rigid active site, but the more accur