Metabolic pathways

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

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.

Induced fit occurs when the active site changes shape to better fit the substrate after the substrate binds.

substrate molecule(s) have a high affinity for the active site and the subsequent products have a low affinity allowing them to leave the active site.

(The binding of the enzyme to its substrate also lowers the activation energy of the reaction (amount of energy needed to make a reaction happen). If an enzyme is present, the amount of energy needed to make a product is lowered. As the products are made, they are no longer specific to the active site (they have a low affinity to the enzyme) and so are released.) Context You need to understand that when an enzyme binds to a substrate it lowers the activation energy for the reaction. that’s all.

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.

Competitive inhibitors bind at the active site preventing the substrate from binding. Competitive inhibition can be reversed by increasing substrate concentration.

Non-competitive inhibitors bind away from the active site but change the shape of the active site preventing the substrate from binding. Non-competitive inhibition cannot be reversed by increasing substrate concentration.

Feedback inhibition occurs when the end- product in the metabolic pathway reaches a critical concentration. The end-product then inhibits an earlier enzyme, blocking the pathway, and so prevents further synthesis of the end-product.