Structure of adenosine triphosphate (ATP), a central intermediate in energy metabolism

Metabolism is the chemical reactions which keep us alive. It happens in the cells of living organisms.

The chemical reactions are catalyzed by enzymes. Metabolism allows organisms to grow, reproduce, maintain their structures, and respond to their environments. The word ‘metabolism’ can also refer to digestion and the transport of substances into and between different cells.

Metabolism is usually divided into two categories:

• Catabolism breaks down organic matter and harvests energy by way of cellular respiration.
• Anabolism uses energy to build molecules such as proteins and nucleic acids.