80 WJEC Biology AS Level - Marianne Izen - 2nd Edition (1.4 Enzymes And Biological Reactions) Flashcards
What is enzyme inhibition?
Enzyme inhibition is the decrease in rate of an enzyme-controlled action by another molecule, an inhibitor.
An inhibitor combines with an enzyme and prevents it forming an enzyme-substrate complex.
What is the shape of a competitive inhibitor?
Competitive inhibitors have a molecular shape complementary to the active site and similar to that of the substrate, so they compete for the active site.
Describe an example of competitive inhibition.
In the mitochondrial matrix, a reaction in the Krebs cycle is catalysed by the enzyme succinic dehydrogenase
Malonic acid has a similar shape to succinic acid and so they compete for the active site of succinic dehydrogenase.
Increasing the concentration of the substrate, succinic acid, reduces the effect of the inhibitor, because the more substrate molecules present, the greater their chance of binding to active sites, leaving fewer available for the inhibitor.
But if the inhibitor concentration increases, it binds to more active sites and so the reaction rate is slower.
Draw a diagram explaining competitive inhibition
What should you do if you are given concentrations of substrate and competitive inhibitor?
Inhibitor (Key-Term)
A molecule or ion that binds to an enzyme and reduces the rate of the reaction the enzyme catalyses.
Competitive inhibition (Key-Term)
Reduction of the rate of an enzyme-controlled reaction by a molecule or ion that has a complementary shape to the active site, similar to the substrate, and binds to the active site, preventing the substrate from binding.
What is end-product inhibition?
Why is it important?
End-product inhibition occurs when a product of a series of reactions inhibits an enzyme that acts earlier in the series so it slows down the whole sequence of reactions.
This is an important way of controlling cell metabolism.
Is the competitive inhibitor permanently bound to the active site?
The competitive inhibitor is not permanently bound to the active site, so when it leaves, another molecule can take its place.
This could be substrate or inhibitor, depending on their relative concentrations.
What happens as the concentration of competitive inhibitor increases?
As the concentration of competitive inhibitor increases, the rate of reaction decreases.
