Lecture 9

Question 1

What is Km?

Answer 1

a concentration expressed in molarity

Question 2

What does Km measure?

Answer 2

measure of substrate concentration required for effective catalysis

Question 3

What do high Km values mean?

Answer 3

you require high substrate concentrations for effective catalysis

Question 4

What do low Km values mean?

Answer 4

enzyme has a higher affinity for the substrate

Question 5

Km is graphically defined as

Answer 5

the substrate concentration required to achieve half of an enzyme’s Vmax

Question 6

What is Vmax?

Answer 6

rate of reaction expressed as some amount per unit time

Question 7

What does Vmax measure?

Answer 7

measures how fast an enzyme can catalyze a reaction at full-speed (meaning all enzyme molecules are saturated with substrate)

Question 8

How is Vmax measured?

Answer 8

measured with a specific enzyme concentration, under specific conditions

Question 9

What does Kcat (turnover number)?

Answer 9

measure of how many substrate molecules are converted per enzyme molecule, per second

Question 10

What are the blood glucose levels in the liver before and after eating a snack?

Answer 10

4.4 mM before, 10 mM after

Question 11

What are the blood glucose levels in the limbs before and after eating a snack?

Answer 11

4.4 mM before, 6.6 mM after

Question 12

Glucokinase is found in

Answer 12

the liver

Question 13

Hexokinase is found

Answer 13

in the limbs

Question 14

Which body structure gets glucose first?

Answer 14

limbs

Question 15

What are the seven factors that influence enzyme-catalyzed reactions?

Answer 15

[E]; [S]; temperature; pH; ionic strength; cofactor concentration; inhibitor/activator concentrations

Question 16

Write out the Michaelis-Menten equation.

Answer 16

write out slide 10

Question 17

What are the four assumptions of the Michaelis-Menten equation.

Answer 17

[E] remains constant; [ES] formation is rapid and remains constant; [S] and other cofactor concentrations is much greater than [E]; reaction proceeds in one direction

Question 18

When do we measure reaction rate?

Answer 18

at a time when substrate depletion is not limiting the reaction

Question 19

LDH catalyzes which reaction? Write it out.

Answer 19

write out slide 24

Question 20

Write out slide 25.

Answer 20

write out

Question 21

Write out Beer-Lambert’s equation, and identify each component.

Answer 21

write out slide 28

Question 22

Beer-Lambert’s equation breaks down at

Answer 22

high concentrations

Question 23

How do we calculate ΔA340nm/min?

Answer 23

record reading at t=0, t=5, find the difference, and then multiply by 12

Question 24

What is the difference between a continuous time course assay and a fixed-time course assay?

Answer 24

Continuous assays are most convenient, with one assay giving the rate of reaction with no further work necessary; Discontinuous assays are when samples are taken from an enzyme reaction at intervals and the amount of product production, or substrate consumption, is measured in these samples

Question 25

Under what conditions would a fixed-time course assay be inappropriate?

Answer 25

If you don’t know concentration range of salt over which a protein of interest will elute; fixed time course assay is bad for doing enzyme kinetic Michaelis-Menten plots

Question 26

Write out the Lineweaver-Burk equation and identify the x and y intercepts.

Answer 26

write out

Question 27

What is the physiological role of LDH enzyme and the NAD+ cofactor?

Answer 27

LDH converts NAD+ to NADH; NADH has an absorbance value that can be measured at 340 nm

Question 28

Under what condition(s) is the conversion of pyruvate to lactate reversible?

Answer 28

pH 8.8 makes reaction reversible; under aerobic conditions, the NADH would be converted back to NAD+ by the electron transport chain; Since that set of reactions can only happen aerobically, the LDH reaction accomplishes the same end under anaerobic conditions