Metabolism

In a nutshell

Metabolism is all of the chemical reactions that happen inside an organism. These reactions are controlled by enzymes. The reactions can build up molecules or break them down.

Building up molecules

Some chemical reactions can build up molecules.

Example

Glucose is an example of a sugar molecule. Lots of glucose molecules can be joined together to form starch, glycogen and cellulose. Starch is a storage molecule in plant cells, glycogen is the equivalent storage molecule in animal cells and cellulose strengthens the plant cell wall.

Example

Lipids are made from three fatty acids and one molecule of glycerol. Glucose is used to make the glycerol which combines with the three fatty acids.

Example

Glucose can be used to make proteins. Sugar molecules will join nitrate ions to form amino acids. Lots of amino acids join together to form proteins.

Breaking down molecules

Some chemical reactions can break down molecules.

Example

Respiration is the process of breaking down glucose into carbon dioxide and water. This process transfers energy to other metabolic reactions in the body such as protein synthesis.

Example

Urea is formed through the breakdown of excess proteins. The urea is then excreted in urine.