Bell Task – complete the following Rate Rate Substrate Conc. Temperature Rate Rate pH Enzyme conc.

Inhibitors It is possible for some other molecule to bind to an active site or other part of enzyme This could inhibit enzyme function.

Competitive Inhibitors Inhibitor binds briefly to the active site The inhibitor is similar to the substrate The inhibitor and the substrate compete for the active site

What affects competitive inhibition? If there is more substrate than inhibitor, the substrate easily binds to active site and the enzyme function unaffected If there is more inhibitor than substrate, it is less likely for the substrate to meet active site and the enzyme function is inhibited

Competitive = Reversible Can be reversed by adding more substrate

Competitive inhibition: example Ethylene glycol is a toxic substance that is converted in the body to oxalic acid. Oxalic acid can cause permanent damage to the kidney. The active site of the enzyme that converts ethylene glycol to oxalic acid also accepts ethanol.

Competitive inhibition Ethanol is an antidote to cure ethylene glycol poisoning. It is a competitive inhibitor. If the poisoned person is given a large dose of ethanol, the ethanol acts a competitive inhibitor, slowing down the reaction of the enzyme of ethylene glycol for long enough to allow the ethylene glycol to be excreted.

Competitive inhibition: example Methanol poisoning occurs because methanol is oxidized to formaldehyde and formic acid which attack the optic nerve causing blindness.

Ethanol is an antidote Ethanol is given as an antidote for methanol poisoning because ethanol competitively inhibits the oxidation of methanol. Ethanol is oxidized in preference to methanol and consequently, the oxidation of methanol is slowed down so that the toxic by-products do not have a chance to accumulate.

Non- Competitive 2 possibilities: Inhibitor binds to different parts of the enzyme – not the active site Inhibitor binds permanently to active site

Binding to other sites Disrupts arrangement of H bonds and hydrophobic interactions Distorts 3-D shape of active site No longer fits substrate

Irreversible or Reversible This depends on how long the inhibitor binds for. Irreversible if inhibitor is bound permanently Reversible if inhibitor is bound temporarily

Example – non competitive Antibiotic penicillin is a non-competitive inhibitor Binds permanently to the active site of an enzyme, produced by bacteria. Penicillin prevents the substrate from binding to the active site. This enzyme is essential for the production of bacterial cell walls. This stops bacteria from reproducing as new bacterial walls are not formed.

Bacterial cell

Inhibition: lethal or useful Inhibition can be lethal e.g. antifreeze example In many situations inhibition is essential Enzymes in most reactions need to be controlled so they don’t constantly churn out product.

End-product inhibition One way to prevent excess product forming is to use the end product of a reaction as an inhibitor. As enzyme is converted to product, the reaction is slowed down as the product binds to the enzyme and prevents the substrate binding.

End-product inhibition It is non-competitive because the end product , does not bind to the active site but to another part of the enzyme. It is reversible because as the amount of the end product fall it does no longer bind to the enzyme and the enzyme regain activity

Medicines: is this true? Those that kill germs are irreversible. Antidotes are competitive or non-competitive but reversible. Those that treat a condition (heart problems, poisoning are reversible)