3 types of Enzyme inhibition, inhibitor mode of action

Question 1

Inhibitor

Answer 1

A molecule that acts directly on enzyme to lower the rate of reaction

• Normal cellular inhibitor (product, feed-back)
• Toxins (nerve gas, venom, cyanide etc.)
• Drugs (penicillin etc.)

Normal inhibitor to reduce overproduction of a molecule
Toxins are induced externally which can be fatal
Drugs are taken in externally for treatment

Question 2

2 groups of inhibitor

Answer 2

Reversible and Non-reversible

Question 3

3 types of reversible inhibition

Answer 3

1. competitive
2. non-competitive
3. uncompetitive

Question 4

Reversible inhibition

Answer 4

On/off inhibition

Question 5

irreversible inhibition

Answer 5

Always on inhibition

Question 6

How to overcome reversible competitive inhibitor

Answer 6

Overcome it by removing it from the enzyme by 2 methods

Dialysis or dilution

Inhibitor is loosely bound to the enzyme by non-covalent bonds.

Question 7

Mechanism of competitive inhibitor

Answer 7

Inhibitor and substrate compete for the same active site. Inhibitor have the same shape as substrate. Increasing the S can outnumber the inhibitor.

This is reversible

Question 8

Mechanism of non-competitive inhibitor

Answer 8

Inhibitor and substrate do not compete for the same active site. Inhibitor have a different shape from substrate. Inhibitor will bind to a allosteric site and change the conformational shape of the enzyme. Non-competitive inhibitor can bind to enzyme before and after reaction.

Increasing S will not overcome its inhibition.

Question 9

Mechanism of uncompetitive inhibitor

Answer 9

Uncompetitive inhibitor can only bind to the ES complex.

Increasing the S favors its inhibition.

Question 10

Vmax and Km of competitive inhibitor vs no inhibitors

Answer 10

Vmax is not changed as there is still a substrate concentration where full enzyme activity can be achieved. Inhibitor can be diluted out by the substrate.

Km is increased as at lower substrate concentrations, inhibitor interferes with the binding between enzyme and inhibitor

Question 11

Vmax and Km of non-competitive inhibitors vs no inhibitors

Answer 11

Vmax is decreased and Km is unchanged.
Km is unchanged as increasing the concentration of the substrate does not reduce this type of inhibition.

Vmax is decreased as fewer functional enzymes leads to fewer available active sites and thus a smaller Vmax.

Question 12

Draw the Michaelis mentis graph for competitive inhibition

Answer 12

Same asymptote

Higher curve than normal

Question 13

Draw the Lineweaver burk graph for competitive inhibition

Answer 13

Cut at the same y intercept for competitive inhibitor

Competitive inhibitor cuts at a smaller x intercept

Question 14

Draw the eadie hofstee graph for competitive inhibition

Answer 14

Slope is much steeper for competitive inhibitor

Vmax, the y intercept cuts as the same point

Question 15

Draw the Michaelis mentis graph for non-competitive inhibition

Answer 15

Lower asymptote

Same level of Km

Question 16

Draw the Lineweaver burk graph for non competitive inhibition

Answer 16

Lower y intercept

Same x intercept

Question 17

Draw the eadie hofstee graph for non competitive inhibition

Answer 17

Same y intercept

Smaller x intercept

Question 18

irreversible inhibition

Answer 18

Cannot be overcome
Inhibitor is tightly bound to the amino acid residues at the active site of the enzyme, thereby permanently inactivating the enzyme.

Question 19

List 2 examples of irreversible inhibition

Answer 19

Nerve gas

Penicillin

Question 20

Penicillin mode of action

Answer 20

Action of penicillin
Penicillin (e.g. cephalosporin) covalently binds to the Ser amino acid in the transpeptidase active site, thereby irreversibly inhibiting the transpeptidase enzyme and preventing bacterial cell wall synthesis
Results in lysis of the bacteria cell

Question 21

Transpeptidase

Answer 21

An enzyme that makes cross-links between peptidoglycan chains in the bacterial cell wall

Question 22

Pencillin

Answer 22

Penicillin binds to a Ser amino acid in the transpeptidase active site and inhibits its action