2.1.4 Enzymes – Inhibitors Flashcards
(13 cards)
What does enzyme specificity mean?
The shape of the active site of an enzyme is complementary to one type of substrate. This substrate is the correct shape to fit the active site and form an enzyme-substrate complex. Any other substrate will not fit.
What is an inhibitor and what does it do?
An inhibitor is a substance that will slow down or stop the action of an enzyme (it inhibits it). It can do this by affecting the way the substrate binds to an enzyme, or the enzyme’s turnover.
What does a competitive inhibitor do?
A competitive inhibitor has a similar shape to an enzymes substrate and so physically competes with the substrate for access to the enzyme’s active site.
How does a competitive inhibitor compete with a substrate?
The competitive inhibitor binds to the active site forming an enzyme-inhibitor complex. The enzyme does not change the shape of the inhibitors and it reduces the number of free active sites therefore slowing the rate of product formation.
What is it called if an inhibitor binds to an enzyme irreversibly?
An inactivator.
What does a non-competitive inhibitor do?
Non-competitive inhibitors do not resemble the shape of the substrate and do not enter the active site. They disrupt the tertiary structure of the enzyme preventing the formation of enzyme-substrate complexes.
How does a non-competitive inhibitor inhibit an enzyme?
It binds to the enzyme at a different location than the active site which is called the allosteric site. It disrupts the tertiary structure by causing the active site to distort so that it is no longer complementary to the substrate. This can be reversible or irreversible.
How can you reduce the effect of a competitive, reversible inhibitor?
You can increase the concentration of substrate so that it is more likely that a substrate molecule collides with the enzyme rather than an inhibitor.
Would increasing the concentration of substrate reduce the effect of a non-competitive reversible inhibitor?
Increasing the substrate concentration would not have a large effect, the maximum rate of reaction would still be reduced.
How can inhibitors be useful in metabolic pathways?
Many metabolic processes have sequences of enzyme-catalysed reactions with the product of one reaction becoming the substrate of the next. The product of the last reaction normally binds to the first enzyme in the reaction which temporarily inhibits the enzyme and prevents accumulation of too much end product.
What happens in a metabolic pathway when the product is in demand again?
When the end product is in demand again the molecule with detach from the first enzyme allowing the pathway to run again. This is an example of negative feedback.
Give two examples of competitive inhibitors?
- Penicillin- this is an irreversible competitive inhibitor which inhibits enzymes involved in the production of bacterial cell walls.
- Arabinose- this is a reversible competitive inhibitor. It competes with glucose for the active site of the glucose oxidase enzyme.
Give two examples of non-competitive inhibitors?
- Digitalis is a non-competitive inhibitor which can be extracted from the foxglove plant. It binds to the enzyme ATPase and increases contractions of the cardiac muscle.
- Cyanide is an irreversible inhibitor of the enzyme cytochrome oxidase which is involved in respiration. It prevents the cells from producing ATP and causes them to die.
