Enzyme Inhibitors 4.3 Flashcards
Reaction Pathways
Reactions don’t normally happen by themselves, they happen in a series of reactions called a reaction pathway. This has to be closely regulated as it is enzyme controlled.
Inhibitor
A molecule that stops an enzyme from carrying out its function, or it can slow it down
Competitive Inhibition
This is when a molecule that has a similar shape to the substrate of an enzyme can bind to the enzymes active site which stops the substrate from binding so, therefore, the enzyme cannot carry out its function
Why is it called competitive inhibition?
It’s called competitive because the substrate and inhibitor are competing with each other to bind to the active site of the enzyme. If you increase your level of inhibitor, they will be more likely to bind so the rate of the reaction will slow down a lot.
How to reduce the inhibitor?
If you increase the concentration of the substrate enough, there will be more substrate binding to the enzyme than the inhibitors so you can still get to the Vmax. It can also be reversible if the inhibitors detach.
Examples of competitive inhibitors
Statin is an example. It’s a drug given to inhibit the synthesis of cholesterol. Another is aspirin which inhibits the synthesis of pain chemicals.
Non-competitive Inhibition
The inhibitor will bind to the allosteric site which is an alternative place apart from the active site. It will alter the tertiary structure of the enzyme so the active site will change shape and no longer be complementary to the substrate.
Why is it called non-competitive inhibition?
It’s called non-competitive because it doesn’t compete with the substrate to bind to the active site, instead it alters the enzyme’s structure so is irreversible.
Can you stop the inhibitor?
Even if you increase the concentration of the substrate or enzyme, you cannot overcome it. You can further decrease the rate of reaction by adding more inhibitor.
Examples of non-competitive inhibitors
Insecticides and herbicides inhibit acetylcholinesterase which is involved in nerve impulse transmission so can cause death.
Can also be PPIs (proton pump inhibitors) which stop hydrogen ions being pumped in the stomach to make it less acid so you don’t form ulcers
End product inhibition
When the product of a reaction is used to inhibit the enzymes that took part in that reaction. This is negative feedback and is an example of non-competitive reversible inhibition.
Examples of end-product inhibition
An enzyme PFK can be used to break down molecules in respiration and ATP inhibits it. So when ATP is high, it stops the reaction so no waste products are made by the breakdown of glucose. When the ATP is used up, there is no ATP to bind to the PFK so it will keep breaking down glucose and make more ATP
