�鶹Լ��

Enzymes control metabolic pathways. The enzymes change the substrate at each step in the metabolic pathway in order to get the final product at the end.

There are different types of metabolic pathways – some are anabolic and some are catabolic.

• Anabolic – this type of pathway requires energy and is used to build up large molecules from smaller ones (biosynthesis).
• Catabolic – this type of pathway releases energy and is used to break down large molecules into smaller ones (degradation).

An example of an anabolic reaction is photosynthesis, where plants make glucose molecules from different raw materials.

An example of a catabolic reaction is the process of food digestion, where different enzymes break down food particles so they can be absorbed by the small intestine.

Metabolic pathways can be reversible or irreversible. Almost all pathways are reversible.

If a specific enzyme or substrate isn’t available in a pathway then sometimes an end product can still be made using an alternative route (another metabolic pathway). This might take longer but still results in the end product that is needed.

Enzymes are vital proteins involved in metabolic pathways. Some enzymes can be found embedded within the cell membrane. Other proteins found embedded within the membrane act as:

• pumps - for example the sodium potassium pump that pumps sodium out of the cell and potassium into the cell.
• pores - which allow ions of a particular size to pass through the membrane.