Chapter 8 Notes

Question 1

Enzymes?

Answer 1

biological catalysts that speed up chemical reactions by several orders of magnitude

Question 2

Enzymes affect __ not reaction equilibria.

Answer 2

reaction rates

Question 3

Substrates?

Answer 3

reactants that bind enzymes

Question 4

__ change the barrier and speed up the reaction.

Answer 4

Enzymes

Question 5

Difference between delta-G and delta-G-prime?

Answer 5

delta-G: tells you if RxN will occur under these conditions

delta-G-prime: tells you under standard conditions if RxN goes to completion

Question 6

How do you find delta-G?

Answer 6

=Delta-G-Prime + RT ln Keq

Question 7

Keq (equilibrum constant) =

Answer 7

[products]/[reactants]

Question 8

Delta-G-Prime =

Answer 8

-RT ln Keq

Question 9

When RxNs will not proceed, what can you add to make them proceed?

Answer 9

more reactants or products

Question 10

Enzyme kinetics vs. enzyme thermodynamics?

Answer 10

enzyme kinetics: relates to speed of RxNs

enzyme thermodynamics: tells you whether a reaction can occur

Question 11

What two things cause activation energy (if in the right orientation) and what facilitates activation energy?

Answer 11

temperature and concentration

enzymes

Question 12

How do enzymes stabilize the transition state?

Answer 12

by lowering the activation energy barrier through binding energy (this is how RxNs occur quickly)

Question 13

Describe the lock and key model.

Answer 13

binding of substrate to enzyme happens at the active site; no enzyme-substrate change; substrate fits exactly into enzyme at active site; complimentary shape on enzyme

Question 14

Describe the induced-fit model.

Answer 14

enzyme changes to fit substrate at active site; binding of substrate induces structure changes in the enzyme

Question 15

Describe the conformational selection model.

Answer 15

selection for conformational substrates for function; pre-knowledge of dynamic properties can be used in drug design; substrate selects for conformation at the active site (fluctuating active sites); enzyme can go back to original state; RNA can act as a biological enzyme

Question 16

How can the effect of enzymes on reaction rates be calculated?

Answer 16

by changing initial concentrations of substrates with time

Question 17

What is the core of enzyme kinetics?

Answer 17

reactant is being consumed/product formed per unit of time

Question 18

How do you measure RxN rates?

Answer 18

using initial velocity since reactants will have different values

Question 19

What are the two assumptions of the Michaelis-Menten Equation?

Answer 19

1) formation of a specific ES complex is a necessary intermediate in catalysis 2) The ES complex eventually achieves a steady state

Question 20

What is the Michaelis-Menten equation?

Answer 20

Vo = Vmax ([S] / (Km + [S]))

Question 21

Forward rate vs. reverse rate?

Answer 21

forward rate: formation of ES complex

reverse rate: breakdown of ES complex

Question 22

When is a double reciprocal (Lineweaver-Burk) plot used instead of a hyperbolic MM curve?

Answer 22

when extracting kinetic parameters

Question 23

Difference between Lineweaver-Burk and MM?

Answer 23

Plot 1/Vo vs. 1/[S] in Lineweaver-Burk rather than Vmax vs. [S]

Question 24

Which is preferred, MM or LB?

Answer 24

LB because it is harder to plot MM hyperbolic curves

Question 25

Km =

Answer 25

Michaelis Constant = (K1 + K2) / K1

Question 26

What does the Kcat/Km depend on?

Answer 26

pH, temperature, and certain conditions

Question 27

In cells, __ value reflects the cellular concentration of substrates and is equal to the dissociation constant (Kd) of ES complex.

Answer 27

Km

Question 28

Kcat?

Answer 28

catalytic turnover number; how much product an enzyme can form when at maximum efficiency

Question 29

When Km is high = __ affinity for reactants.

Answer 29

low

Question 30

When Km is low = __ affinity for reactants.

Answer 30

high