1.4.3 - Enzyme inhibition

Question 1

what are enzyme inhibitors?

Answer 1

substances that slow down enzymes or stop them from working

Question 2

what is reversible inhibition?

Answer 2

inhibition of the action of an enzyme by an inhibitor that does not permanently affect the functioning of the enzyme and can be removed from the enzyme

• often used to control reaction rates within a cell
• common feature of metabolic pathways

Question 3

what is irreversible inhibition?

Answer 3

inhibition of the action of an enzyme that is permanent and can’t be undone

• it is never used within cells to control the rate of reactions
• tends to occur more slowly than other forms of inhibition
• e.g cyanide and mercury

Question 4

what are the 2 main forms of reversible inhibition?

Answer 4

competitive inhibition

non-competitive inhibition

Question 5

what is competitive inhibition?

Answer 5

inhibition in which the inhibitor molecule is similar in shape to the substrate molecule and competes with it for the active site of the enzyme

• affected by both inhibitor and substrate concentrations
• it forms an enzyme / inhibitor complex

Question 6

what is non-competitive inhibition?

Answer 6

inhibition in which the inhibitor does not compete for the active site but forms a complex with the enzyme or enzyme / substrate complex and changes the shape of the active site so it can no longer catalyse the reaction

• affected only by concentration of inhibitor
• these inhibitors do not bind to the active site

Question 7

what is the process of irreversible inhibition?

Answer 7

• inhibitor combines with the enzyme by permanent covalent bonding to one of the groups vital for catalysis to occur
• changes the shape and structure in such a way it cannot be reversed
• the enzyme is inactivated permanently

Question 8

what are regulatory enzymes?

Answer 8

enzymes that have a site separate to the active site where another molecule can bind to have either an activating or inhibitory effect

• brings about non-competitive inhibition
• found in complex metabolic pathways (e.g photosynthesis and respiration)

Question 9

what is end-product inhibition?

Answer 9

a control system in many metabolic pathways in which an enzyme at the beginning of the pathway is inhibited by one of the end products of the reaction
- feedback control gives a simple and effective way of controlling the rate of several reactions at once