Lecture 9

Question 1

How do enzymes work as catalysts?

Answer 1

By providing an alternate path of lower activation energy

Question 2

What is a progress curve?

Answer 2

A curve displaying the measures of the appearance of produce (or disappearance of substrate) with time

Question 3

Where is velocity measured from on a progress curve?

Answer 3

From the linear proportion; initial velocity

Question 4

Why can the parabolic portion of a progress curve not be used to measure velocity?

Answer 4

There are too many unknowns

Question 5

What is the relationship between enzyme and velocity?

Answer 5

Linearly proportional

Question 6

What are the effects of an infinite substrate concentration?

Answer 6

Increases in a linear way however as all active sites within the enzyme become occupied, the ROR stops increasing = Vmax

Question 7

What order of reaction is the linear portion of the progress curve?

Answer 7

First order, rate is dependent upon substrate concentration

Question 8

What order of reaction is the parabolic portion of the progress curve?

Answer 8

Zeroth order, rate is not dependent on substrate concentration

Question 9

How can Vmax be increased?

Answer 9

By adding more enzyme and therefore more active sites

Question 10

What is the Michaelis constant?

Answer 10

Km; the substrate concentration required to generate half the Vmax

Question 11

What is the Michaelis-Menten equation?

Answer 11

V = Vmax [S] / Km + [S]

Question 12

What are the simplifying assumptions of Michaelis-Menten model?

Answer 12

Product is not converted back to substrate, Haldane’s steady-state assumption, only measuring initial ROR means that [S] does not change over time ( [S] > [E] )

Question 13

What is Haldane’s steady-state assumption?

Answer 13

The rate of ES complex formation is equal to the rate of its breakdown d[ES] / d t = 0

Question 14

What is the Lineweaver-Burk plot

Answer 14

Plotting the inverse of the Michaelis parabolic plot to get a linear plot

Question 15

What is the y-intercept of the Lineweaver-Burk plot?

Answer 15

1 / Vmax

Question 16

What is the x-intercept of the Lineweaver-Burk plot?

Answer 16

-1 / Km

Question 17

What is the slope of the Lineweaver-Burk plot?

Answer 17

Km / Vmax

Question 18

What are the units of Km

Answer 18

Concentration so; mmol / L

Question 19

What does a low Km relate to?

Answer 19

High affinity for bonding to that particular substrate

Question 20

What does a high Km relate to?

Answer 20

Low affinity for bonding to that particular substrate

Question 21

In a cell, what is the typical range of [S]?

Answer 21

Often around or below the Km value, meaning that rate control is effective and substrates aren’t queuing for active sites

Question 22

What is Kcat?

Definition

Answer 22

The turnover number; the number of substrate molecules converted to product, per enzyme, per time

Question 23

What conditions is Kcat measured under?

Answer 23

Enzyme is saturated with substrate

Question 24

What is Kcat?

Measure of…

Answer 24

The catalytic activity of an individual enzyme molecule

Question 25

What does k2 represent in terms of enzymes?

Answer 25

The rate of production of enzyme and product from ES (enzyme-substrate complex)

Question 26

What value is Kcat equivalent to?

Answer 26

k2

Question 27

What is the relationship between Kcat, Vmax and [E]?

Answer 27

Kcat = Vmax/[E]

Question 28

What are the relative values of Kcat and Km that an enzyme must have to be highly catalytically efficient?

Answer 28

High Kcat, low Km

Question 29

What ratio shows the efficiency of an enzyme?

Answer 29

Kcat/Km

Question 30

If Kcat/Km is high, what is the efficiency of an enzyme?

Answer 30

High efficiency

Question 31

If Kcat/Km is low, what is the efficiency of an enzyme?

Answer 31

Low efficiency