Enzymes

Question 1

What is the name of an active enzyme which has a bound cofactor?

Answer 1

holoenzyme

Question 2

What is Km?

Answer 2

Km is an indicator of the affinity of the enzyme for its substrate. The higher the Km, the lower the affinity.

Question 3

What is the influence of non-competitive inhibitors (reversible) on Km and Vmax?

Answer 3

The Km value does not change - still need the same amount of substrate to reach 1/2 Vo.

The Vmax decreases because the enzyme is being “removed” by the inhibitor. So, in effect, you have less enzyme available.

Question 4

What does it mean when (S) = Km?

Answer 4

the rate of reaction is at half its maximal value

Question 5

Define Km

Answer 5

the concentration of substrate required to produced half of the maximum velocity (Vmax) in a given reaction

Question 6

How does free energy (delta G) relate to the spontaneity of a reaction?

Answer 6

a negative delta G is associated with a spontaneous reaction, with a lot of energy released.

Question 7

How does the presence of an irreversible inhibitor effect Km and Vmax?

Answer 7

no effect on Km

Vmax will decrease

Question 8

What is the difference between inducing and activating an enzyme?

Answer 8

inducing an enzyme means that you are increasing the genetic expression of an enzyme.

activating an enzyme causes an already existing enzyme to increase its output.

Question 9

How does the presence of a noncompetitive (reversible) inhibitor affect Km and Vmax?

Answer 9

no effect on Km

Vmax will decrease

Question 10

Can Km be altered by changing enzyme or substrate concentrations?

Answer 10

no

Question 11

List the three classes of enzyme inhibitors.

Answer 11

competitive (reversible), non-competitive (reversible), and irreversible

Question 12

What is delta G if a system is at equilibrium?

Answer 12

zero -> no net change can take place

Question 13

How can we tell if a reaction will occur spontaneously?

Answer 13

if delta G is negative, the reaction is exergonic and therefore spontaneous

Question 14

Enzyme A has a Km of 3 units for a certain reaction and enzyme B has a Km of 12 units for the same reaction. which enzyme has a greater affinity for the substrate is this reaction?

Answer 14

enzyme A

Question 15

What is “activation energy”?

Answer 15

the difference in free energy between transition state and substrate. AKA Gibb’s free energy of activation.

Question 16

If an enzyme has a very high Km, what does this mean?

Answer 16

the enzyme achieves a high rate of catalysis only at very high concentrations of substrate

Question 17

What is an apoenzyme?

Answer 17

an enzyme that requires a cofactor to be active

Question 18

how does the presence of a competitive (reversible) inhibitor affect Km and Vmax?

Answer 18

Km will increase

Vmax will stay the same

Question 19

How does the presence of an irreversible (inactivator) inhibitor affect Km and Vmax?

Answer 19

no effect on Km

Vmax will decrease

Question 20

Is Vmax affected by competitive inhibitors?

Answer 20

Vmax is unaffected because you retain the same amount of enzyme. the inhibitor can be overcome by higher substrate concentrations.

Question 21

The free energy of activation describes the ___ of the reaction.

Answer 21

the rate of reaction (largely unrelated to the delta G of the reaction)

Question 22

How does Km reflect the affinity between enzyme and substrate?

Answer 22

the lower the Km, the greater the affinity (enzyme for the substrate)