Lecture 9 - Measuring and Comparing the Activities of Enzymes

Question 1

What does a progress curve do?

Answer 1

Measures the appearance of product or disappearance of substrate with time

Question 2

When is initial reaction velocity measured?

Answer 2

At/near time zero

Question 3

What happens if there is sufficient excess of substrate?

Answer 3

As the amount of enzyme increases, the rate of reaction increases

Question 4

With fixed amount of enzyme, what occurs when excess substrate is added

Answer 4

Curve increases linearly

Question 5

What happens to the curve when all active sites become occupied?

Answer 5

Rate of reaction stops increasing, previously linear curve starts to slope.

Question 6

Zero order kinetics:

Answer 6

Rate does not depend on substrate concentration

Question 7

First order kinetics:

Answer 7

Rate depends on substrate concentration

Question 8

What does Vmax equal to?

Answer 8

Maximum velocity possible, when there is infinite substrate.

Question 9

What does KM equal to?

Answer 9

Substrate concentration at which Velocity = Half Vmax

Question 10

The V vs [S] curve is described by?

Answer 10

The Michaelis-Menten equation

Question 11

What is the Michaelis-Menten equation?

Answer 11

Question 12

What are the assumptions for the Michaelis-Menten equation?

Answer 12

1. Product is not converted back to substrate.
2. Haldane’s stead state assumption (rate of enzyme substrate complex formation = rate of breakdown) [ES] / Time = 0
3. Measuring initial rates of reaction means that the substrate concentration does not significantly change over time.

Question 13

What is the name of the straight line plot?

Answer 13

Lineweaver-Burk plot.

Question 14

Plotting ___ and ___ gives the Lineweaver-Burk plot

Answer 14

1/V and 1/[S]

Question 15

What is on the X-axis on the Lineweaver-Burk plot?

Answer 15

1/[S]

Question 16

What is on the Y-axis on the Lineweaver-Burk plot?

Answer 16

1/V

Question 17

Y-intersection = ?

Answer 17

1/Vmax

Question 18

X-intersection = ?

Answer 18

-1/KM

Question 19

What is the slope equation?

Answer 19

KM / Vmax

Question 20

Low KM =

Answer 20

high affinity for that particular substrate.

Question 21

High KM =

Answer 21

low affinity for that particular substrate.

Question 22

KM = KD =

Answer 22

dissociation constant for that substrate pair.

Question 23

How Is binding and catalyses described?

Answer 23

An enzyme, E, converts a single substrate, S, to a single product P that is instantly released.

Question 24

What do the relative speeds of K1 and K-1 do?

Answer 24

Define how tightly substrate binds

Question 25

What is the rate of catalysis?

Answer 25

K2

Question 26

What does K2 relate to?

Answer 26

Energy of activation for the transition state

Question 27

KM = ? (equation)

Answer 27

k-1 / k1

Question 28

Is KM the same for each substrate?

Answer 28

No

Question 29

What does the turnover number kcat show?

Answer 29

Number of substrate molecules converted to product, per enzyme, per unit of time when E is saturated with [S]. Helps to define the activity of one enzyme molecule

Question 30

The ‘peak’ enzyme should have?

Answer 30

A high kcat and a low KM

Question 31

Kcat / KM is an overall measure of what?

Answer 31

Enzyme efficiency