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 pathways.
- Reactions within metabolic pathways can 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.
Enzyme Action
- Induced fit occurs when the active site changes shape to better fit the substrate after the substrate binds.
- Induced fit lowers activation energy required for the reaction as the substrate is more closely bound to the active site.
- The 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 rate of enzyme reaction can be affected by substrate concentration.
- As the substrate concentration increases, the enzyme reaction increases until all of the active sites are occupied by the substrate.
- At this point, adding more substrate makes no difference to the reaction rate.
- 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.
Types of inhibition
- 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.
