Enzyme Inhibitors in a Snap! Unlock the full A-level Biology course at bit.ly/2I9DVh4 created by Adam Tildesley, Biology expert at SnapRevise and graduate of Cambridge University.
The key points covered of this video include:
1. Enzyme reaction rates
2. The effect of temperature
3. The effect of pH
4. Enzyme and substrate concentrations
Enzyme Inhibition
We have seen how enzymes can be activated by cofactors. Enzymes can also be deactivated by molecules called inhibitors. Inhibitions are any molecule that reduces or stop a reaction. Adding a small concentration of an inhibitor will reduce the rate of reaction. If an excess of an inhibitor is added to a solution then the reaction may be prevented completely.
Competitive Inhibitors
One type of inhibitor is called a competitive inhibitor. It fits into the active site of an enzyme instead of the substrate. These inhibitor form a physical barrier that prevents the formation of enzyme-substrate-complexes. Because both inhibitor and substrate can fit into the active site they compete with each other for the enzyme.
Non-Competitive Inhibitors
The other type of inhibitors is non-competitive inhibitors. Non-competitive inhibitors bind to a separate part of an enzyme called its allosteric site. Binding of a non-competitive inhibitor causes a conformational change in the enzyme. This change alters the shape of the enzyme's active site so that it is not complementary with its substrate. Because these inhibitors do not bind to the active site they do not compete with substrates - hence their name.
Comparing Enzyme Inhibitors
Competitive and non-competitive inhibitors work in different ways. Non-competitive inhibitors have a powerful inhibition effect. Competitive inhibitors have a less powerful inhibition effect. A graph of both inhibitor effects is a good way to compare the two. Most competitive inhibitors bind reversibly. Most non-competitive inhibitors bind permanently. This table summarises the differences between competitive and non-competitive inhibitors.
End-Product Inhibition
We have already seen how enzymes can work together to complete metabolic processes. Most of the time a cell will only want a certain amount of a molecule being produced. In some cases, one of the products acts as an inhibitor to another enzyme in the pathway. When the inhibitor non-competitive and the last product in the pathway it is called end-product inhibition. If the concentration of the final product is high, then more inhibition will occur. Greater inhibition will lead to a decrease in the amount of end product being produced. Inhibition also decreases if the concentration of the end product decreases. This is an example of a negative feedback loop which ensures the concentration of a product stays roughly constant.
Summary
Enzyme activity can be reduced or stopped with inhibitors
Non-competitive inhibitors bind to allosteric sites and have a strong inhibition effect
Competitive inhibitors bind to active sites and have a weaker inhibition effect
End-product inhibition relies on non-competitive inhibition to keep the concentration of metabolic products roughly constant in a cell