Enzymes

Enzymes are globular proteins that catalyse the many thousands of metabolic reactions taking place within cells and whole organisms. The molecules that participate in these enzyme-catalysed reactions are called metabolites, and cellular metabolism as a whole consists of interconnected chains and cycles of such reactions - including respiration, photosynthesis, protein synthesis and many other pathways. These reactions fall into two broad categories: anabolic reactions build up larger organic molecules from smaller ones (for example, synthesising proteins from amino acids, or polysaccharides from simple sugars), while catabolic reactions break larger molecules down into smaller ones (for example, digesting complex food, or breaking down sugar during respiration). Enzymes may also be classified by where they act: extracellular enzymes are secreted out of the cell and work extern …