Block 2 - Enzyme Kinetics and Inhibition Flashcards Preview

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Flashcards in Block 2 - Enzyme Kinetics and Inhibition Deck (15):
1

What is the velocity of a reaction?

The disappearance of [reactant] or the formation of [product] per unit time, and is a function of the concentration of the reactant.

2

Describe the differences between zero order, first order, and second order reactions?

0, 1, and 2 indicated the power to which the substrate is taken in the equation. When the power is 0, it implies that the substrate has no effect on the reaction rate. When the power is 1, it implies that as the substrate increases by a factor r, the reaction rate will increase by a factor r. When the power is 2, it implies that as the substrate increases by a factor of r, the reaction rate will increase by r^2.

3

At very low [S], what pseudo-order reaction rate is occuring? Why?

Peusdo-first order because as substrate increases, reaction rate increases equally.

4

At very high [S], what is the pseaudo-order reaction rate? Why?

Pseudo-zero order because since most/all enzymes are filled and we have approached or reached Vmax, the reaction rate cannot increase any further and is therefore not relying on an increase in [S] to increase.

5

What is Km? What is the difference between enzymes with a low Km and high Km?

Km equals the substrate concentration at (1/2)Vmax. Enzymes with a low Km have a high affinity to their substrate, as opposed to enzymes with a high Km which have a low affinity for their substrate.

6

What are two implications of having a low Km?

Less substrate is required to reach half Vmax.
Formation of ES is more rapid that breakdown of ES.

7

What is the turnover number? What equation can be used to calculate it?

Turnover number is Kcat (k3), and is also the rate limiting step. If Vmax and [Etotal] are known, Kcat can be calculated.

8

What is a Lineweaver-Burk plot? Why is it used?

It is a transformation of the Michaelis-Menten plot and is used since Vmax cannot be accurately deduced from the Michaelis-Menten plot.

9

The x-intercept of a Lineweaver-Burk plot is a negative reciprical of what value?

Km

10

The y-intercept of a Lineweaver-Burk plot is a negative reciprocal of what value?

Vmax

11

What is competitive inhibition? What enzyme site is involved? Is Km and/or Vmax affected?

The inhibitor competes with the substrate for the active site and is typically structurally similar to the substrate. The inhibitor can only bind to free enzyme. Km is increased by a factor of alpha but Vmax remains the same.

12

What is noncompetitive inhibition? What enzyme site is involved? Is Km and/or Vmax affected?

Non-competitive inhibitors do not bind to the active site and therefore can bind to free enzyme or enzyme-substrate complexes. Vmax is decreased by a factor of alpha but Km remains the same.

13

What often acts as a noncompetitive inhibitor in the body by interacting with the -SH groups on enzymes?

Many heavy metal ions such as Hg or Pb

14

What is uncompetitive inhibition? What enzyme site is involved? Is Km and/or Vmax affected?

Uncompetitive inhibitors only bind to the ES complex, therefore they do not compete with the substrate for the active site. Both Km and Vmax are decreased

15

How is catalytic efficiency calculated? Is a higher or lower value better?

Kcat/Km, higher is better.