Enzymes : mechanisms and kinetics

Question 1

How does enzyme work

Answer 1

work by reducing the energy barrier or free energy of activation (∆G) by bringing the substrates to closer to the enzyme at the active site.

Question 2

what are the factors influencing the rx rates?

Answer 2

1. pH
2. Enzyme concentration
3. Substrate concentration
4. Stability of the enzyme substrate complex
5. Concentration of the products
6. Temperature
7. ionic strength

Question 3

what is the effect of ionic strength on the rxn rate

Answer 3

low salt concentration can help enzyme but high concentrations will force the enzyme to go in solution and decrease the rxn rate

Question 4

what is the end-point method?

Answer 4

End point assay in which substrate is incubated with the enzyme for a fixed period of time. The reaction is stopped and the amount of product formed or substrate used is estimated.

Question 5

What are the disadvantages of end point method

Answer 5

• over time the enzyme lose activity
• there is a substrate depletion
• products may inhibit enzymes

Question 6

What are the advantages of initial rate method

Answer 6

it is a true measure of the rate of the enzyme activity because no product has formed to cause inhibition and the substrate concentration is at the maximum.

Question 7

what are the three phases of enzyme reactions?

Answer 7

A transient phase or pre-steady phase
B steady state phase
C exhaustation phase or post steady phase

Question 8

in the post steady phase, the rxn rate is ____

Answer 8

decreasing

Question 9

in the pre-steady phase, the rxn rate is ___

Answer 9

increasing

Question 10

In the steady phase, the rxn rate is ____

Answer 10

constant

Question 11

in the pre-steady phase

Answer 11

k1 > k2 + k3

Question 12

in the steady phase

Answer 12

k1 = k2 + k3

Question 13

in the post-steady phase

Answer 13

k2 + k3 > k1

Question 14

What is the michealis menten equation of V0

Answer 14

V0 = Vmax * [S] / Km + [S]

Question 15

What is the lineweaver - burke plot

Answer 15

1/V0 = Km / Vmax * 1/[S] + 1/Vmax

Question 16

What is the Km ?

Answer 16

the substrate concentration at which the V0 is equal to half of the Vmax. Km is the ratio of k2 + k3 / k1. So when km is high the affinity for the enzyme is low because there is more breakdown than formation. When the Km is low, it means that the affinity is high.

Question 17

Lower is the Km, better is _____

Answer 17

the affinity of the enzyme to the substrate

Question 18

What is the Vmax ?

Answer 18

Vmax is the maximum rate of a reaction. it is rached when the enzyme is saturated.

Question 19

What does the Vmax / km ratio measures

Answer 19

the catalytic efficiency

Question 20

What type of enzyme inhibition is this : Strong covalent bond at the active site of the enzyme.

Answer 20

irreversible

Question 21

What type of enzyme inhibition is this : : non-covalent interaction

Answer 21

reversible

Question 22

What are the three type of reversible inhibition?

Answer 22

1. competitive
2. non competitive
3. uncompetitive

Question 23

Describe competitive inhibition and give an example

Answer 23

the inhibtor will bind at the active site and prevent the binding of the substrate.
ex : inhibition of succinate dehydrogenase by malonate

Question 24

Describe non-competitive inhibition and give an example

Answer 24

can act as both competitive inhibitor and uncompetititive becuse the inhibitor binds to a site other than the active site.
ex : inhibition of the Rx rate by the pH

Question 25

Describe uncompetitive inhibition and give an example

Answer 25

The inhibitor binds to a site that is only available after the substrate has bound to the active site.
ex : inhibition of invertse by high sucrose concentration