inhibitors

Question 1

What is an inhibitor?

Answer 1

A substance which slows the rate of reaction down on an enzyme- controlled reaction

Question 2

What is a competitive inhibitor?

Answer 2

A molecule which has a similar shape to the substrate of an enzyme, allowing for it to bind to the active site and block it and therefore stop the reaction. This is called an enzyme-inhibitor complex

Question 3

What is a non-competitive inhibitor?

Answer 3

An inhibitor which binds to another site on the enzyme called the allosteric site. This still causes the active site to change shape so that the substrate molecule can no longer fit, but it does not compete with the substrate.

Question 4

What is end product inhibition?

Answer 4

• where the final end product in a metabolic pathway acts as a regulator
• when the amount of end product is high, it binds non-competitively to an enzyme in the pathway, blocking further production of itself

Question 5

Why are some medical drugs classed as enzyme inhibitors?

Answer 5

• An antiviral drug uses a reverse transcriptase inhibitor to prevent viral DNA from replicating
• penicillin inhibits transpeptidase which forms the protein to synthesis bacterial cell walls

Question 6

What does a metabolic poison do and give an example of an inhibitor involved in respiration?

Answer 6

• they interfere with metabolic reactions in cells
• cyanide is a non competitive inhibitor of cytochrome C oxidase

Question 7

what is a reversible inhibitor?

Answer 7

stops or reduces enzyme activity temporarily

Question 8

what is an irreversible inhibitor?

Answer 8

forms covalent bonds and inhibits permanently

Question 9

explain one way in which oxygen could act as an inhibitor (2 marks)

Answer 9

oxygen could act as a reversible inhibitor and bind to the active site

Question 10

explain the effects if enzyme, substrate conc and competitive inhibitors on the rate of enzyme controlled reactions (9 marks)

Answer 10

• increase in substrate conc = increase in enzyme activity, more successful collisions, more substrate available for active site
  – however, eventually slows down as all available sites will be saturated
• increase in enzyme conc = more successful collisions, increases rate of reaction, greater likelihood of enzyme substrate complex formation
• inhibitor = enters active site so substrate cannot bind, reaction rate is reduced