Metabolic Pathways

Metabolic pathways are integrated and controlled pathways of enzyme catalysed reactions within a cell They can have reversible steps, irreversible steps and alternative routes

Reactions within metabolic pathways can either be anabolic or catabolic Anabolic reactions build up large molecules from small molecules and require energy Catabolic reactions break down large molecules into smaller molecules and release energy

Metabolic pathways are controlled by the presence or absence of particular enzymes, and the regulation of the rate of reaction of key enzymes

During an enzyme controlled reaction the substrate molecule(s) attaches to the active site on the enzyme. The substrate molecule(s) have high affinity for the active site The active site changes shape to better fit the substrate after the substrate binds - this is called an induced fit This lowers the activation energy required for the reaction to occur The subsequent products have a low affinity allowing them to leave the active site

Some metabolic reactions are reversible and the presence of a substrate or the removal of a product will drive a sequence of reactions in a particular direction