Test 3

Question 1

How does a catalyst increase the rate of reaction?

Answer 1

it allows reacting molecules to more easily form the transition state

Question 2

Which of the following amino acids would be most likely found in the active site of an enzyme that uses acid-base catalysis

Answer 2

Histidine

Question 3

In an enzyme mechanism that generates a negative energy charge in the transition state, which of the following would be most effective to have in the active site of the enzyme?

Answer 3

Transition metal cation

Question 4

If the Asp of the chymotrypsin active site was mutated to another amino acid, which of the following would be considered an invisible mutation in that it is least likely to impact the function of the enzyme?

Answer 4

Asp –> Glu

Question 5

During the first half of the chymotrypsin mechanism where the acyl-enzyme intermediate is formed, what role does His play?

Answer 5

general base then general acid

Question 6

When the transition state is formed, what is the specific interaction observed between Asp and His that helps stabilize the transition state?

Answer 6

low-barrier hydrogen bond

Question 7

A plot of velocity versus substrate concentration for a simple enzyme-catalyzed reaction produces a _______. This indicates that at some point, the enzyme is _____.

Answer 7

Hyperbolic curve; saturated with substrate

Question 8

How is the enzyme-catalyzed reaction affected by the addition of more enzyme?

Answer 8

Velocity will increase

Question 9

Which of the following must be true if the steady state assumption is to be used?

Answer 9

d[ES]/dt = 0

Question 10

An extremely efficient enzyme has a _____ Km and a _____ Kcat.

Answer 10

small; large

Question 11

Enzyme studies were conducted for tryosinase enzyme in the presence and absence of the inhibitor dodecyl gallate, as illustrated in the plots below. What is the value of the Km in the ABSENCE inhibitor?

Answer 11

For Lineweaver plot, Km is calculated from the x-intercept. Hence Km = 1mM

Question 12

An inhibitor of aldehyde dehydrogenase was designed. The Michaelis-Menten plot of the enzyme activity without and with two different concentrations of inhibitor is below. What is the Km and Vmax values for each of the assay samples based off the Michaelis-Menten plot?

Answer 12

VMax doesn’t change, Km is 1/2 of Vmax on the line

Question 13

A positive deltaG means what for spontaneity?

Answer 13

Unfavorable; unspontaneous

Question 14

A negative deltaG means what for spontaneity?

Answer 14

Spontaneous reaction

Question 15

What is glyceraldehyde-3-phosphate dehydrogenase doing in this reaction? (Glycolysis)

Answer 15

Catalyzing the reaction

Question 16

If this reaction was carried out at 25C, what would be the equilibrium constant for the reaction be? Remember -DeltaG = RT ln K, R =8.315 J/mol X K

Answer 16

Change the delta G to JOULES instead of KJ; so -6300 J/mol = 8.315 J/mol (298K) lnK
Solving for K: Keq = 0.078

Question 17

What are coupled reactions? Illustrate with an example.

Answer 17

Whenever a thermodynamically UNFAVORABLE reaction (deltaG Positive) is paired with favorable reaction (deltaG negative) or in other words spontaneous reaction drives the overall non-spontaneous one. Example Hexokinase reaction.

Question 18

Which of the following represents the net products of glycolysis from ONE molecule of glucose?

Answer 18

2 pyruvate, 2 NADH, 2 ATP

Question 19

With a deltaG of -16.7 kJ/mol, the reaction catalyzed by hexokinase is considered to be

Answer 19

Metabolically irreversible

Question 20

Which of the following enzymes requires ATP as a substrate?

Answer 20

phosphofructokinase

Question 21

What enzyme catalyzes the major regulatory step of glycolysis?

Answer 21

phosphofructokinase

Question 22

Which of the following is a potent activator of phosphofructokinase in mammals?

Answer 22

fructose-2,6-biphosphate

Question 23

The enzyme responsible for the synthesis of fructose-2,6-biphosphate is ____.

Answer 23

phosphofructokinase-2

Question 24

Triose phosphate isomerase catalyzes a reaction that is most similar to _____.

Answer 24

phosphoglucose isomerase

Question 25

What is the name for the process that produces ATP from ADP in glycolysis?

Answer 25

substrate-level phosphorylation

Question 26

What is the greatest driving force for the reaction catalyzed by pyruvate kinase?

Answer 26

tautomerization of enol pyruvate to pyruvate

Question 27

Which of the following contains a high energy bond that is used for a substrate-level phosphorylation in glycolysis?

Answer 27

1,3-biphosphoglycerate

Question 28

What regulatory enzyme of glycolysis is skipped during fructose metabolism?

Answer 28

phosphofructokinase

Question 29

What coenzyme is required for the conversion of pyruvate to oxaloacetate?

Answer 29

biotin

Question 30

What would occur if both phosphofructokinase and fructose bisphosphatase were active simultaneously?

Answer 30

a futile cycle

Question 31

Gluconeogenesis is most active in the ____>

Answer 31

Liver

Question 32

Fructose-2,6-bisphosphate is an activator of ____ and an inhibitor of ____.

Answer 32

phosphofructokinase; fructose bisphosphatase

Question 33

Which of the following correctly relates the order of intermediates during the synthesis of glycogen?

Answer 33

glucose –> glucose-6-phosphate–>glucose-1-phosphate —> UDP-glucose —>glycogen

Question 34

In glycogen synthesis, what is the intermediate between glucose-1-phosphate and glycogen?

Answer 34

UDP-Glucose

Question 35

The main enzyme of glycogen catabolism is _____, which catalyzes a ____ reaction.

Answer 35

glycogen phosphorylase; phosphoroylsis

Question 36

The conversion of glucose-1-phosphate to UDP-glucose has a deltaG near zero. Which of the following reactions is coupled with the above to drive it to completion?

Answer 36

Hydrolysis of PPi

Question 37

Fructose-2,6-bisphosphate

Answer 37

is an indicator of high cellular glucose concentration

Question 38

Which of the following enzymes is an oxidoreductase?

Answer 38

Glyceraldehyde-3-phosphate dehydrogenase

Question 39

Which of the following enzymes catalyzes an irreversible process?

Answer 39

Pyruvate Kinase

Question 40

Which of the following is the ketogenic amino acid?

Answer 40

Lysine

Question 41

Which of the following enzymes will catalyze committed step in glycolysis?

Answer 41

Phosphofructokinase 1