Chapter 14- Enzyme Inhibition

Question 1

Inhibitors are substances that interfere with ______ by _______ enzymatic reactions

Answer 1

catalysis
slowing or halting

Question 2

Two classes of inhibitors:

Answer 2

• Reversible
• Irreversible

Question 3

Reversible inhibitors use _____ bonds that form ____ but break _____

Answer 3

weak
rapidly
easily

Question 4

Which type of inhibitor does not permanently disable the enzyme?

Answer 4

reversible inhibitors

Question 5

Reversible inhibitors come to an equilibrium with the enzyme to form ____

Answer 5

enzyme inhibitor complex (EI)

Question 5

Irreversible inhibitors are known as:

Answer 5

enzyme inactivators

Question 5

Irreversible inhibitors combine with enzymes through _____

Answer 5

strong (usually) covalent bond

Question 5

An enzyme is ___ when paired with an irreversible inhibitor

Answer 5

permanently disabled

Question 6

irreversible inhibitors are ______ dependent

Answer 6

time

Question 7

for irreversible inhibitors, you cannot apply____

Answer 7

Michaelis-Menton kinetics

Question 8

Depending on their nature, reversible inhibitors will effect____ or _____

Answer 8

Km
Vmax

Question 9

Km and Vmax are measured in _______ which gives the ____

Answer 9

presence of inhibitor
apparent Km or Vmax

Question 10

Competitive inhibitors _____ with substrate binding

Answer 10

compete

Question 11

The substrate and competitive inhibitor are typically ____

Answer 11

mutually exclusive

Question 12

Competitive inhibitors typically binds ____- to the enzyme

Answer 12

reversibly

Question 13

The winner of the competition between competitive inhibitors and substrates depends on the ______

Answer 13

the concentration of each.

Question 14

Competitive inhibitors bind to _____ but not to _____

Answer 14

free enzyme
ES complex

Question 15

Competitive inhibitors will _____ Km, because ____

Answer 15

increase
because there is no affinity for S when EI has been made which reduces affinity and increases Km

Question 16

Competitive inhibitors will ___ Vmax, because ____

Answer 16

not change
Vmax is the velocity of very high [S] which means inhibitor will not inhibit the enzyme bc it is out competed and doesn’t slow down the rxn

Question 17

Uncompetitive inhibitor is ____ of binding to free E

Answer 17

incapable

Question 18

Uncompetitive inhibitors only bind to the _____

Answer 18

ES complex

Question 19

How do uncompetitive inhibitors inactivate the enzyme?

Answer 19

causes structural distortion of the active site

Question 20

Effect of low [S] on uncompetitive inhibitors

Answer 20

inhibitor cannot bind bc most enzyme are free, making the inhibitor ineffective

Question 21

Effect of high [S] on uncompetitive inhibitors

Answer 21

Inhibitor can bind bc most E is in ES complex, making the inhibitor effective.

Question 22

Effect of high [Inhibitor] on competitive inhibitors

Answer 22

able to bind because [S] is out-competed which reduces [free Enzyme]

Question 23

Effect of high [S] on competitive inhibitor

Answer 23

S out-competes inhibitor which makes it ineffective

Question 24

Uncompetitive inhibitor effect on Km, why??

Answer 24

Decreases Km
effectively reduces [ES] which pulls the equilibrium towards [ES]. This increases the amount of S that binds to E which increases the affinity

Question 25

uncompetitive inhibitor effect on Vmax. Why?

Answer 25

Decrease Vmax
inhibitor effective at high [S], effectively reduces [ES] and [E]. Vmax= K2[E]

Question 26

Competitive inhibition effect on Lineweaver Burke plot:

Answer 26

• No incr in Km
• No change in Vmax

Question 27

Uncompetitive inhibition effect on Lineweaver Burke plot:

Answer 27

Both Km and Vmax are decreased
leading to parallel lines

Question 28

Noncompetitive inhibitors can bind to ___

Answer 28

either E or ES

Question 29

Noncompetitive inhibitors will bind to _____

Answer 29

a site remote from the active site

Question 30

Noncompetitive inhibitors prevent E from ___

Answer 30

turning substrate into product

Question 31

With noncompetitive inhibitors, EI and ESI are ____

Answer 31

un reactive

Question 32

Two classes of mixed inhibitors

Answer 32

1. pure noncompetitive
2. Mixed noncompetitive

Question 33

Pure noncompetitive inhibitors

Answer 33

binding of I does not affect S binding (rare case)

Question 34

Mixed noncompetitive inhibitors

Answer 34

binding of inhibitor reduces affinity of S for E (or ES)

Question 35

How does pure noncompetitive inhibition affect Km and Vmax?

Answer 35

• Km is unchanged
• Vmax is decreased

Question 36

Why do pure noncompetitive inhbitors decrease Vmax?

Answer 36

reduces [ES] and [E] which reduces the total amount of enzyme, slowing the reaction

Question 37

How does mixed noncompetitive inhibitors affect Km?

Answer 37

when K1<K1’ then Km increases
when K1>K1’ then Km decreases

Question 38

How do mixed noncompetitive inhibitors affect Vmax?

Answer 38

Vmax is decreased in both cases of K1 and K1’