Lecture 9 - Enzyme Kinetics

Question 1

What is Enzyme Kinetics

Answer 1

How enzymes affect the rate of chemical reactions

Question 2

Michaelis Menten Equation

Answer 2

Vo = Vmax [S] / Km + [S]
Vo = initial velocity
Km = Michaelis Constant
- different for each enzyme and substrate
- affected by conditions such as pH, temp
[S] = substrate concentration
Vmax = maximum velocity of enzyme
- different for each enzyme and substrate
- also called limiting velocity

Question 3

What happens when the enzyme concentration decreases in a Michaelis Menten graph?

Answer 3

Vmax decreases

Km stays the same

Question 4

Lineweaver-Burk Plot

Answer 4

Reciprocal of v and [S]
Able to estimate Vmax from y-int
Able to estimate Km from x-int

Question 5

Significance of Km

Answer 5

Gives idea of concentration of substrate required to achieve Vmax and saturate the active site of the enzyme
Estimate affinity of enzyme for substrate
Approximate value of intracellular level of substrate

Question 6

Efficiency and Capacity of an Enzyme

Answer 6

Efficiency - how much is produced in a certain time

Capacity - how much substrate can be handled by enzyme

Question 7

Kcat

Answer 7

Turnover number
Measure of maximal catalytic activity of the enzyme
Amount of substrate converted to product per amount of enzyme in unit time when the enzyme is operating near Vmax
kcat = Vmax/[Et]
[Et] = total enzyme

Question 8

Enzyme Inhibition

Answer 8

Binds to enzyme and decreases its activity
Use of inhibitors helps us understand how enzymes work
Treatment of poisoning may be addressed by less toxic inhibitors

Question 9

Types of Enzyme Inhibition

Answer 9

Reversible and Irreversable

Question 10

Types of Reversible Enzyme Inhibition

Answer 10

Competitive 
- inhibitor binds at same site as substrate 
- affects only Km
Mixed 
- inhibitor binds at a site different from substrate
- affects Vmac or Km or both
- changes Vmax/Km
Uncompetitive
- Inhibitor binds to ES complex
- affects both Vmax and Km
- no change on Vmax/Km

Question 11

Types of Irreversible Enzyme Inhibition

Answer 11

Partial
Incomplete
Produces same graph of when the concentration of enzyme is lowered
- Same Km and higher 1/Vmax

Question 12

What distinguishes reversible inhibitors from irreversible inhibitors?

Answer 12

Reversible inhibitors are not covalently bound to enzymes but irreversible inhibitors are
There is an equilibrium between bound and unbound reversible inhibitors
There usually is very little reverse reaction for the binding of an irreversible inhibitor