Enzyme inhibitors 4.3 Flashcards
what are inhibitors
inhibitors are molecules that prevent enzymes from carrying out their normal function of catalysis ( or slow them down).
what are the 2 types of inhibition
competitive and non-competitive
how does competitive inhibition work
-A molecule or part of a molecule that has a similar shape to the substrate of an enzyme can fit into the active site of the enzyme
-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
why is it called ‘competitive’ inhibition
Substrate and inhibitor molecules present in a solution will compete with each other to bind to the active sites of the enzymes catalysing the reaction.
This will reduce the number of substrate molecules binding to active sites in a given time and slows the rate of reaction.
For this reason such inhibitors are called competitive inhibitors and the degree of inhibition will depend on the relative concentrations of substrate, inhibitor and enzymes
Does competitve inhibition permenantly change the structure of the enzyme
Most competitive inhibitors only bind temporarily to the active site of the enzyme, so their effect is reversible. However there are some exceptions such as aspirin
how does competitive inhibition effect the rate of reaction
A competitive inhibitor reduces the rate or reaction for a given concentration of substrate, but it does not change the Vmax of the enzyme it inhibits.
if the substrate concentration is increased enough there will be so much more substrate than inhibitor that the original Vmax can till be reached
how does non-competative inhibition work
-The inhibitor binds to the enzyme at a location other than the active site, This alternative site is called an allosteric site
-The binding of the inhibitor causes the tertiary structure of the enzyme to change, meaning the active site changes shape
-This results in the active site no longer having a complementary shape to the substrate so its it unable to bind to the enzyme
-The enzyme cannot carry out its function and it is said to be inhibited
what is an allosteric site
The allosteric site is a site that allows molecules to either activate or inhibit (or turn off) enzyme activity. It’s different than the active site on an enzyme, where substrates bind.
why is non-competitve inhibition non-competitve
As the inhibitor does not compete with the substrate for the active site it is called a non-competitive inhibitor
what is the effect of non-competitive inhibition on the rate of reaction
- decreases rate of reaction
- increasing concentration of enzyme/substrate will not increase rate
- Increasing concentration of inhibitor will decrease rate further
whats the difference between the graph produced by competitve and non-competitve inhibitors
what Is meant by end-product inhibition
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. This serves as a negative-feedback control mechanism for the reaction
what type of inhibitor is an end-product inhibitor
it is an example of non-competitive reversible inhibitor
what is an example of an end-product inhibitor and what is the biology behind the reaction
ATP
the first step involves the addition of 2 phosphate groups to the glucose molecule. The addition of the 2nd phosphate group, which results in the initial breakdown of the glucose molecule, is catalysed by the enzyme phosphofructokinase.
This enzyme is competitively inhibited by ATP
Give an example of how an end-product inhibitor acts as a negative-feedback control mechanism
-When the levels of ATP are high, more ATP binds to the allosteric site on PFK, preventing the addition of the second phosphate group to glucose. Glucose is not broken down and ATP is not produced at the same rate
-As ATP is used up, less binds to PFK and the enzyme is able to catalyse the addition of a 2nd phosphate group to glucose. Respiration resumes, leading to the production of more ATP
