4.3 : Enzyme Inhibitors Flashcards
What are inhibitors ?
Molecules that prevent enzymes from carrying out their normal function of catalysis ( or slow them down)
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.
Substrate and inhibitor molecules will complete with each other to bind to the active site. This reduces the number of substrate molecules binding to the active site in a given time and slows down rate of reaction.
Is competitive inhibition reversible or irreversible?
Most of the times it is reversible, except for some such as aspirin
What is the effect of competitive inhibition on rate of reaction?
It reduces rate of reaction
Doesn’t change the Vmax of the enzyme
If substrate concentration is increased enough, there will be so much more substrate than inhibitor, the original Vmax can still be reached.
Give some examples of competitive inhibition
Statins - used in cholesterol synthesis. Helps people reduce blood cholesterol concentration.
Aspirin - inhibits active site of COX enzymes, preventing synthesis of prostaglandins and thromboxane , the chemicals responsible for producing pain and fever.
How does non competitive inhibition work?
Inhibitor binds to the enzyme at a location other than the active site ( allosteric site ).
This causes the tertiary structure of the enzyme to change, mewing the active site changes shape.
The active site is no longer complementary in shape to the substrate. It cannot carry out its function and is inhibited.
What is the effect of non competitive inhibition on rate of reaction?
Increasing concentration of enzyme or substrate will not overcome effect of a non-competitive inhibitor.
Increasing the concentration of inhibitor will decrease rate of reaction as more active sites become unavailable.
Give some examples of non competitive inhibitors
Organophosphates - used an insecticide and herbicides. Inhibit acetyl cholinesterase, an enzyme necessary for nerve impulse transmission. This can lead to cramps, paralysis and even death if ingested.
Proton pump inhibitors ( PPIs ) - treat long term indigestion. Block enzyme system responsible for secreting hydrogen ions into stomach. Effective in reducing production of excess acid which can lead to stomach ulcers.
What is end product inhibition?
A 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 negative - feedback control mechanism for reaction. Excess products are not made and resources are not wasted.
Give an example of end product inhibition
When two phosphate groups are added to glucose, it breaks down. This is catalysed by PFK. It is competitively inhibited by ATP.
When ATP is 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 second phosphate group. Respiration resumes, leading to more production of ATP.
