2.1.4 Enzymes - Enzyme inhibitors Flashcards
How are enzymes activated?
Enzymes are activated by cofactors, or inactivated with inhibitors.
What are inhibitors?
Inhibitors are molecules that prevent enzymes from carrying out their normal function of catalysis (or slow them down).
What is competitive inhibition?
The substrate and the inhibitor have a similar shape, this means that they are competing to fit into the active site.
If the inhibitor fits into the active site then this blocks the substrate from entering the active site, preventing the enzyme from catalysing the reaction. The enzyme cannot carry out its function and is said to be inhibited.
Most competitive inhibitors bind temporarily therefore it is reversible.
What is the effect of competitive inhibitors on the rate of reaction?
A competitive inhibitor reduces the rate of reaction for a given concentration of substrate, but it doesn’t change the Vmax of the enzyme it inhibits (since it is a potential value).
What is an example of competitive inhibition?
Statins – used in the synthesis of cholesterol.
Aspirin – irreversible inhibits the active site of COX enzymes, preventing the synthesis of prostaglandins and thromboxane, the chemicals responsible for producing pain and fever.
What is non-competitive inhibition?
Enzyme has an active site and an allosteric site. The inhibitor binds to the allosteric site. The binding of the inhibitor causes the tertiary structure of the enzyme to change, therefore the active site changes shape (and so does the function of the enzyme). This results in the active no longer having a complementary shape to the substrate so it is unable to bind to the enzyme. The enzyme cannot carry out its function and is said to be inhibited.
What is the effect of non-competitive inhibitors on the rate of reaction?
Increasing the concentration of inhibitors, decreases the rate of reaction further as more active sites become unavailable. However, increasing the concentration of enzyme or substrate will not overcome the effect of a non-competitive inhibitor.
Non-competitive inhibitors do not reach Vmax value.
What is end-product inhibition?
Is the term used for enzyme inhibition that occurs when the product of a reaction acts as an inhibitor to the enzyme that produces it.
Similar to negative-feedback.
(Binds to the active site or allosteric site and prevents any further reactions from occurring).
