Enzyme inhibition

Inhibitors

Substances that bind to an enzyme and reduce its activity.

Reversible inhibitors

Bind temporarily to an enzyme via weak bonds

Irreversible inhibitors

Bind permanently to an enzyme via strong bonds.

Competitive inhibitors

Compete with the substrate to bind to the active site

Non-competitive inhibitors

Bind to an allosteric site on the enzyme which changes the shape of the active site.

What is the effect of increasing substrate concentration in the presence of competitive inhibitors

The same Vmax can be reached at higher concentrations of substrate as there will be more frequent collisions between the active site and substrate.

What is the effect of increasing substrate concentration in the presence of non-competitive inhibitors

A lower Vmax is reached, as the substrate cannot bind to the inhibited enzymes.

End-product inhibition

When the final product in a metabolic pathway can act as a reversible inhibitor of an enzyme near the beginning of the pathway.

How is end-product inhibition an example of negative feedback

An increase in the concentration of the end product, will decrease the rate of reaction and so decreases its concentration.

Why is the end-product a reversible inhibitor

So that it can be quickly reversed and the rate of reaction increased when the end product concentration decreases.

Why is an enzyme at the start of a metabolic pathway inhibited

To avoid wasting resources making unnecessary intermediates.

Other ways of controlling metabolism

Covalent modification

Compartmentalisation

Controlling the synthesis of enzymes

Covalent modification

Enzymes are synthesised in an inactive form, and are activated when needed.

Compartmentalisation (as a way of controlling metabolism)

Membranes control which substances enter or leave cell or organelle.

How do multi-enzyme complexes increase enzyme efficiency

They maintain the substrate in the vicinity of the next enzyme in the metabolic pathway and reduce diffusion time.

What occurs to the Vmax when irreversible inhibitors are present.

Decreases over time as more enzymes become inactivated.

What is the main use of irreversible inhibitors

Poisons (ingested) and venoms (injected)