2.4 enzyme inhibition Flashcards
How does a competitive inhibitor stop enzyme substrate complexes forming?
Blocking the active site so substrate molecules can not bind
How is a competitive inhibitor able to block the active site?
It has a similar shape to the substrate molecules
What do the competitive inhibitor and substrate molecules have to do?
Compete for the active site
What does a competitive inhibitor do?
Prevents enzyme substrate complexes forming
What is the degree of inhibition dependant on?
The the relative concentrations of substrate and inhibitors
What will happen if there is a high concentration of competitive inhibitors?
- More of the active sites will be taken up (blocked)
- hardly any substrate will get to the enzyme
- lower rate of reaction
What will happen if there is a higher concentration of substrate than competitive inhibitor?
• increased chance of substrate getting to the active site
Are competitive inhibitors usually reversible or non reversible?
Reversible
What does a inhibitor being reversible or irreversible depend on?
The strength of the bonds between enzyme and inhibitor
If the inhibition is irreversible what are the bonds like?
- strong covalent bonds
* hard to remove inhibitor
If the inhibition is reversible what are the bonds like?
- weak hydrogen or weak ionic bonds
* weakness means inhibitor can be removed
Where to non competitive inhibitors bind to?
The enzymes allosteric site
What do non competitive inhibitors binding to the allosteric site cause?
Change in the enzymes tertiary structure
What effect does a change in the enzymes tertiary structure have?
Active sites shape is altered
If the active site of an enzyme changes shape what can no longer happen?
- The enzyme and substrate no longer bind
* enzyme can no longer catalase reactions
State what a Non competitive inhibitor does and the effect it has:
- binds to allosteric site
- changes tertiary structure
- alters shape of active site
- substrate can’t bind
- reactions can’t be catalysed
Do non competitive inhibitors change the active site permanently or temporarily?
Permanently
What effect does increasing substrate concentration have with a non competitive inhibitor?
No effect
Are non competitive inhibitors reversible or non reversible?
Both
Give examples of competitive inhibitors?
Stains
Aspirin
Are stains reversible or irreversible?
Reversible
What do stains do?
Inhibit the enzyme
Give an example of where stains are used:
In cholesterol synthesis to reduce blood cholesterol concentration, lowering the risk of heart disease
Is aspirin reversible or irreversible?
Irreversible
What does aspirin do?
- Inhibits the active site of cox enzymes
* prevents the synthesis of chemicals responsible for producing pain and fever
Give examples of non competitive inhibitors:
- organophosphates
* proton pump inhibitors
What are organophosphates?
A spray used as insecticide herbicides
What do organophosphates do?
Inhibit the enzyme acetyl cholinesterose which is used for nerve impulse transmissions
What do proton pump inhibitors do?
Block the enzyme responsible for secreting H+ ions into the stomach
What are proton pump inhibitors used for?
The treatment of long term indigestion
What medicinal drugs are enzyme inhibitors?
- some antiviral drugs e.g reverse transcriptase inhibitors
* some antibiotics e.g penicillin
What do reverse transcriptase inhibitors do?
Inhibit the enzyme reverse transcriptase which catalysed the replication of DNA, this prevents the virus from replicating
What does penicillin do?
- Inhibits the enzyme transpeptidase which catalysed the formation of proteins in bacteria cell walls
- this weakens the cell wall
- cell bursts bacteria dies
The metabolic poison cyanide is a inhibitor how does it work?
Inhibits enter cytochrome c oxidase an enzyme catalysing respiration reactions, cells that can’t respire die
What does the metabolic poison arsenic do?
Inhibits pyruvate dehydrogenase an enzyme catalysing respiration reactions
What is a metabolic pathway?
Product of 1st reaction involved in second reaction
What is product inhibition?
When product of one reaction inhibits enzyme of another
What is end product inhibition?
Where the last product of metabolic pathway inhibits the enzyme in first reaction
End product inhibition decreases rate of reaction and therefore product production so what happens?
Less inhibition
Causing activated enzymes
More reactions
More products
Why is end product inhibition useful?
Way of controlling the amount of end product made and controlling metabolic reactions
Give an example of end product inhibition
Phosphofructokinaise enzyme involved in glucose breakdown to make ATP
ATP inhibits the enzyme limiting ATP production
