BCCB2000 Lecture 19 Questions

Question 1

The anaplerotic reactions related to the citric acid cycle allow the cycle to be: A. a source of biosynthetic precursers B. the major pathway for generation of ATP C. a source of ATP if oxygen is available D. always based on six-carbon molecules E. controlled allosterically by ATP

Answer 1

A. a source of biosynthetic precursers

Question 2

A deficiency in thiamine causes the disease beriberi. Which might you expect to have a higher than normal blood concentration in an individual with this condition? A. glucose B. isocitrate C. pyruvate D. oxaloacetate E. acetyl CoA

Answer 2

C. pyruvate

Question 3

True or False? The mechanism of pyruvate dehydrogenase complex is an example of metabolite channeling.

Answer 3

True

Question 4

Which of the following cofactors is required for the conversion of succinate to fumarate in the citric acid cycle? A. ATP B. biotin C. FAD D. NAD+ E. NADP+

Answer 4

C. FAD

Question 5

True or False? The overall goal of the citric acid cycle is to oxidize pyruvate, form reduced coenzymes, and produce ATP.

Answer 5

True

Question 6

The citric acid cycle oxidizes pyruvate, and some of the pathway intermediates are starting materials for many biosynthetic pathways. This means the citric acid cycle is ________. A. amplifying B. amphiteric C. amphibolic D. anaplerotic

Answer 6

C. amphibolic

Question 7

True or False? The citric acid cycle may be viewed as a multi-step catalyst simply because it returns to its original state after each round of reactions.

Answer 7

True

Question 8

The TCA cycle involves the following: A. eight enzyme catalysed steps, the production of 2 NADH, the production of 1 FADH2, and the production of 1 GTP B. eight to nine enzyme catalysed steps, the production of 3NADH, the production of 1 FADH2, and the production of 1 GTP C. eight enzyme catalysed steps, the production of 3 NADH, the production of 2 FADH2, and the production of GTP D. ten enzyme catalysed steps, the production of 2 NADH, the production of 1 FADH2, and the production of GTP E. eight enzyme catalysed steps, the production of 2 NADH, the production of 2 FADH2, and the production of GTP

Answer 8

B. eight to nine enzyme catalysed steps, the production of 3NADH, the production of 1 FADH2, and the production of 1 GTP

Question 9

Which of the following is not an intermediate of the citric acid cycle? A. oxaloacetate B. citrate C. α-ketoglutarate D. succinyl-CoA E. acetyl-CoA

Answer 9

E. acetyl-CoA

Question 10

Most of the energy released in citric acid cycle reactions is conserved in ________. A. GTP B. ATP C. NADH D. ADP

Answer 10

C. NADH

Question 11

Which of the following enzymatic activities would you expect to be decreased by thiamine deficiency? A. succinate dehydrogenase B. isocitrate dehydrogenase C. fumarase D. pyruvate dehydrogenase E. malate dehydrogenase

Answer 11

D. pyruvate dehydrogenase

Question 12

True or False? The carbon atoms that enter the citric acid cycle via acetyl CoA are the same ones released as carbon dioxide during one round of the citric acid cycle.

Answer 12

False

Question 13

The role of the Krebs Cycle is to: A. generates energy directly from acetoacetylCoA, provides NADH for the electron transport chain, and provides energy in the form of ATP from substrate level phosphorylation B. generates energy directly from pyruvate, provides NADPH for the electron transport chain, and provides energy in the form of ATP from substrate level phosphorylation C. generates energy directly from acetyl CoA, provides NADH for the electron transport chain, and provides energy in the form of GDP from substrate level phosphorylation D. generates energy directly from acetyl CoA, provides NADPH for the electron transport chain, and provides energy in the form of ADP from substrate level phosphorylation E. generates energy directly from acetyl CoA, provides NADH for the electron transport chain, and provides energy in the form of GTP from substrate level phosphorylation

Answer 13

E. generates energy directly from acetyl CoA, provides NADH for the electron transport chain, and provides energy in the form of GTP from substrate level phosphorylation

Question 14

Which of the following is not required for the oxidative decarboxylation of pyruvate to form acetyl-CoA? A. NAD+ B. lipoic acid C. ATP D. CoA-SH E. FAD

Answer 14

C. ATP

Question 15

In eukaryotes the enzymes of the citric acid cycle are found in the ________. A. cytosol B. mitochondria C. nucleus D. endoplasmic reticulum

Answer 15

B. mitochondria

Question 16

In mammals, each of the following occurs during the citric acid cycle except: A. metabolism of acetate to carbon dioxide and water. B. oxidation of acetyl-CoA. C. formation of α-ketoglutarate. D. net synthesis of oxaloacetate from acetyl-CoA. E. generation of NADH and FADH2.

Answer 16

D. net synthesis of oxaloacetate from acetyl-CoA.

Question 17

Few genetic differences in the enzymes of the TCA cycle are known or reported because: A. no one has studied mutations in the enzymes of the TCA cycle B. the enzymes are not susceptible to mutations C. there are too few mutations in these stable enzymes D. mutations of enzymes in the TCA cycle would be incompatible with life E. mutations are difficult to detect in TCA enzymes

Answer 17

D. mutations of enzymes in the TCA cycle would be incompatible with life

Question 18

True or False? ATP is consumed by the pyruvate dehydrogenase complex during the synthesis of acetyl CoA.

Answer 18

False

Question 19

Which combination of cofactors is involved in the conversion of pyruvate to acetyl-CoA? A. NAD+, biotin, and TPP B. TPP, lipoic acid, and NAD+ C. pyridoxal phosphate, FAD, and lipoic acid D. biotin, FAD, and TPP E. biotin, NAD+, and FAD

Answer 19

B. TPP, lipoic acid, and NAD+

Question 20

The arrangement of subunits in the PDH(pyruvate dehydrogenase) complex ensures that ________. A. ATP is formed B. the product of one enzyme is delivered to the next in turn C. the dihydrolipoamide arm can react with NAD+ D. acetyl CoA enters into the series of reactions

Answer 20

B. the product of one enzyme is delivered to the next in turn

Question 21

True or False? The citric acid cycle is an anaerobic pathway that occurs in the mitochondria of eukaryotes.

Answer 21

False

Question 22

True or False? Pyruvate translocase is specific for transporting pyruvate across the inner mitochondrial membrane.

Answer 22

True

Question 23

A research student isolates all the enzymes of the TCA cycle and adds oxaloacetate and acetyl CoA. The student also adds the appropriate energy precursors, cofactors, and water. Which of the following will most likely not be a direct product of the experiment? A. ATP B. GTP C. NADH D. CO2 E. FADH2

Answer 23

A. ATP

Question 24

Carbons from acetyl CoA are transferred to the citric acid cycle. Which round of the citric acid cycle could possibly release a carbon atom originating from this acetyl CoA? A. first round B. second round C. third round D. fourth round

Answer 24

B. second round

Question 25

Which is not produced by the citric acid cycle? A. NADH B. FMN C. CO2 D. GTP

Answer 25

## Footnote B. FMN

Question 26

Pyruvate translocase is a protein that transports ________. A. pyruvate and H+ in opposite directions B. only pyruvate C. pyruvate and H+ in the same direction D. pyruvate and CO2 in opposite directions

Answer 26

## Footnote C. pyruvate and H+ in the same direction

Question 27

Which cofactor is not used by the pyruvate dehydrogenase complex? A. lipoamide B. thiamine pyrophosphate C. FAD D. QH2

Answer 27

## Footnote D. QH2

Question 28

The conversion of 1 mol of pyruvate to 3 mol of CO2 via pyruvate dehydrogenase and the citric acid cycle also yields _____ mol of NADH, _____ mol of FADH2, and _____ mol of ATP (or GTP). A. 3; 2; 0 B. 4; 2; 1 C. 4; 1; 1 D. 3; 1; 1 E. 2; 2; 2

Answer 28

## Footnote C. 4; 1; 1