2.4 enzyme inhibition

Question 1

How does a competitive inhibitor stop enzyme substrate complexes forming?

Answer 1

Blocking the active site so substrate molecules can not bind

Question 2

How is a competitive inhibitor able to block the active site?

Answer 2

It has a similar shape to the substrate molecules

Question 3

What do the competitive inhibitor and substrate molecules have to do?

Answer 3

Compete for the active site

Question 4

What does a competitive inhibitor do?

Answer 4

Prevents enzyme substrate complexes forming

Question 5

What is the degree of inhibition dependant on?

Answer 5

The the relative concentrations of substrate and inhibitors

Question 6

What will happen if there is a high concentration of competitive inhibitors?

Answer 6

• More of the active sites will be taken up (blocked)
• hardly any substrate will get to the enzyme
• lower rate of reaction

Question 7

What will happen if there is a higher concentration of substrate than competitive inhibitor?

Answer 7

• increased chance of substrate getting to the active site

Question 8

Are competitive inhibitors usually reversible or non reversible?

Answer 8

Reversible

Question 9

What does a inhibitor being reversible or irreversible depend on?

Answer 9

The strength of the bonds between enzyme and inhibitor

Question 10

If the inhibition is irreversible what are the bonds like?

Answer 10

• strong covalent bonds

* hard to remove inhibitor

Question 11

If the inhibition is reversible what are the bonds like?

Answer 11

• weak hydrogen or weak ionic bonds

* weakness means inhibitor can be removed

Question 12

Where to non competitive inhibitors bind to?

Answer 12

The enzymes allosteric site

Question 13

What do non competitive inhibitors binding to the allosteric site cause?

Answer 13

Change in the enzymes tertiary structure

Question 14

What effect does a change in the enzymes tertiary structure have?

Answer 14

Active sites shape is altered

Question 15

If the active site of an enzyme changes shape what can no longer happen?

Answer 15

• The enzyme and substrate no longer bind

* enzyme can no longer catalase reactions

Question 16

State what a Non competitive inhibitor does and the effect it has:

Answer 16

• binds to allosteric site
• changes tertiary structure
• alters shape of active site
• substrate can’t bind
• reactions can’t be catalysed

Question 17

Do non competitive inhibitors change the active site permanently or temporarily?

Answer 17

Permanently

Question 18

What effect does increasing substrate concentration have with a non competitive inhibitor?

Answer 18

No effect

Question 19

Are non competitive inhibitors reversible or non reversible?

Answer 19

Both

Question 20

Give examples of competitive inhibitors?

Answer 20

Stains

Aspirin

Question 21

Are stains reversible or irreversible?

Answer 21

Reversible

Question 22

What do stains do?

Answer 22

Inhibit the enzyme

Question 23

Give an example of where stains are used:

Answer 23

In cholesterol synthesis to reduce blood cholesterol concentration, lowering the risk of heart disease

Question 24

Is aspirin reversible or irreversible?

Answer 24

Irreversible

Question 25

What does aspirin do?

Answer 25

• Inhibits the active site of cox enzymes

* prevents the synthesis of chemicals responsible for producing pain and fever

Question 26

Give examples of non competitive inhibitors:

Answer 26

• organophosphates

* proton pump inhibitors

Question 27

What are organophosphates?

Answer 27

A spray used as insecticide herbicides

Question 28

What do organophosphates do?

Answer 28

Inhibit the enzyme acetyl cholinesterose which is used for nerve impulse transmissions

Question 29

What do proton pump inhibitors do?

Answer 29

Block the enzyme responsible for secreting H+ ions into the stomach

Question 30

What are proton pump inhibitors used for?

Answer 30

The treatment of long term indigestion

Question 31

What medicinal drugs are enzyme inhibitors?

Answer 31

• some antiviral drugs e.g reverse transcriptase inhibitors

* some antibiotics e.g penicillin

Question 32

What do reverse transcriptase inhibitors do?

Answer 32

Inhibit the enzyme reverse transcriptase which catalysed the replication of DNA, this prevents the virus from replicating

Question 33

What does penicillin do?

Answer 33

• Inhibits the enzyme transpeptidase which catalysed the formation of proteins in bacteria cell walls
• this weakens the cell wall
• cell bursts bacteria dies

Question 34

The metabolic poison cyanide is a inhibitor how does it work?

Answer 34

Inhibits enter cytochrome c oxidase an enzyme catalysing respiration reactions, cells that can’t respire die

Question 35

What does the metabolic poison arsenic do?

Answer 35

Inhibits pyruvate dehydrogenase an enzyme catalysing respiration reactions

Question 36

What is a metabolic pathway?

Answer 36

Product of 1st reaction involved in second reaction

Question 37

What is product inhibition?

Answer 37

When product of one reaction inhibits enzyme of another

Question 38

What is end product inhibition?

Answer 38

Where the last product of metabolic pathway inhibits the enzyme in first reaction

Question 39

End product inhibition decreases rate of reaction and therefore product production so what happens?

Answer 39

Less inhibition
Causing activated enzymes
More reactions
More products

Question 40

Why is end product inhibition useful?

Answer 40

Way of controlling the amount of end product made and controlling metabolic reactions

Question 41

Give an example of end product inhibition

Answer 41

Phosphofructokinaise enzyme involved in glucose breakdown to make ATP
ATP inhibits the enzyme limiting ATP production