Kreb's Cycle

Question 1

Which statement about the oxidative decarboxylation of pyruvate in aerobic conditions in animal cells is CORRECT?

Answer 1

One of the products of the reactions of the pyruvate dehydrogenase complex is a thioester of acetate.

Question 2

Which reaction of the citric acid cycle requires a water molecule?

a) formation of citrate
b) succinyl-CoA to succinate
c) fumarate to malate
d) All of the answers are correct

Answer 2

All of the answers are correct

Question 3

Which statement about NAD + and NADH is TRUE?

Answer 3

NADH inhibits the pyruvate dehydrogenase complex.

Question 4

Which statement is NOT true of the reaction catalyzed by the pyruvate dehydrogenase complex?

Answer 4

Biotin participates in the decarboxylation.

Question 5

How much carbon dioxide is produced from the complete aerobic catabolism of one molecule of 2-phosphoglycerate via catabolic pathways?

Answer 5

3 CO2

Question 6

The glyoxylate cycle is:

Answer 6

a means of using acetate for both energy and biosynthetic precursors

Question 7

Which enzyme catalyzes a reversible reaction under normal cellular conditions?

Answer 7

succinate dehydrogenase

Question 8

Covalent modification is one way the activity of specific enzymes can be regulated. Which enzyme is NOT regulated in this way?

Answer 8

a-ketoglutarate dehydrogenase

Question 9

Which enzyme in the citric acid cycle has a standard free energy that is large and positive?

Answer 9

malate dehydrogenase

Question 10

Which statement about the oxidative decarboxylation of pyruvate in animal cells is CORRECT?

Answer 10

It only occurs under aerobic conditions.

Question 11

Which enzymatic activity would be decreased by thiamine deficiency?

Answer 11

a-ketoglutarate dehydrogenase complex

Question 12

In mammals, what process does NOT occur during the citric acid cycle?

Answer 12

net synthesis of oxaloacetate from acetyl-CoA

Question 13

Which three of the choices listed are possible sources for acetyl-CoA that enters the citric acid cycle?

1. oxidative decarboxylation of pyruvate
2. B-oxidation of fatty acids
3. catabolism of certain amino acids
4. citrate
5. carboxylation of pyruvate

Answer 13

Oxidative decarboxylation of pyruvate
B-oxidation of fatty acids
Catabolism of certain amino acids.
1,2 and 3.

Question 14

Which cofactor is required for the conversion of fumarate to succinate?

Answer 14

FADH2

Question 15

Which citric acid cycle intermediate is chiral?

Answer 15

Malate

Question 16

Which statement is FALSE with respect to the pyruvate dehydrogenase complex?

Answer 16

The proximity of the catalytic enzymes in the cluster slows down the overall rate.

Question 17

Which cofactors associated with the pyruvate dehydrogenase complex are classified as prosthetic groups?

1) TPP
2) lipoate
3) CoA-SH
4) NAD +
5) FAD

Answer 17

1,2 and 5

TPP, Lipoate, FAD

Question 18

Which high-energy bond is associated with the succinyl-CoA synthetase reaction?

a) acyl phosphate
b) thioester
c) phospho-histidine
d) mixed anhydride
e) All of the answers are correct.

Answer 18

E) All of the answers are correct.

Question 19

Entry of acetyl-CoA into the citric acid cycle is DECREASED when:

Answer 19

the ratio of [ATP]/[ADP] is high.

Question 20

During seed germination, the glyoxylate pathway is important to plants because it enables them to:

Answer 20

carry out the net synthesis of glucose from acetyl-CoA.

Question 21

Why is flux through the citric acid low in the resting state?

Answer 21

Flux through the cycle is low due to low local concentrations of NAD+ because of a diminished rate of oxidative phosphorylation.

Question 22

The glyoxylate cycle in germinating seeds is a pathway that has some similarity to the citric acid cycle. It uses the carbon-based products from the catabolism of fatty acids as the precursors for gluconeogenesis. How can the glyoxylate cycle accomplish this?

Answer 22

Its reactions bypass the decarboxylation steps of the citric acid cycle.

Question 23

What process occurs in the citric acid cycle?

Answer 23

formation of a mixed anhydride (acyl phosphate)

Question 24

Conversion of 1 mol of acetyl-CoA to 2 mol of CO 2 and CoA via the citric acid cycle results in the net production of:

Answer 24

1 mol of FADH2.

Question 25

Which combination of cofactors is involved in the conversion of pyruvate to acetyl-CoA?

Answer 25

TPP, lipoic acid, and NAD+