Unit 3 - Lecture Quizzes

Question 1

The African naked mole-rat’s (Heterocephalus glaber) social and subterranean lifestyle generates a hypoxic niche. Under experimental conditions, naked mole-rats tolerate hours of extreme hypoxia and survive 18 minutes of total oxygen deprivation (anoxia) without apparent injury. During anoxia, the naked mole-rat switches to anaerobic metabolism fueled by fructose, which is actively accumulated and metabolized to lactate in the brain. Global expression of the GLUT5 fructose transporter and high levels of ketohexokinase were identified as molecular signatures of fructose metabolism.

Assume fructose 1-phosphate is the dominant pathway in naked mole rats, how could fructose metabolism promote resistance to anoxia?

a) Fructose metabolism avoids feedback inhibition of glycolysis via phosphofructokinase.
b) Fructose metabolism provides alternative fuel source for naked mole rats’ survival in anoxia.
c) Fructose metabolism hyperactivates pyruvate kinase by the accumulated fructose 1,6 bisphosphate.
d) Fructose metabolism yields more ATP for naked mole rats’ survival in anoxia.

Answer 1

a) Fructose metabolism avoids feedback inhibition of glycolysis via phosphofructokinase.

Question 1

Which of the following statements best describes the Warburg effect?

a) The enhanced glucose uptake and utilization by cancer cells even in the presence of oxygen.
b) The preferential utilization of fatty acids instead of glucose by cancer cells.
c) The conversion of lactate into pyruvate as a metabolic adaptation in cancer cells.
d) The reduced reliance on glycolysis for energy production by cancer cells.

Answer 1

a) The enhanced glucose uptake and utilization by cancer cells even in the presence of oxygen.

Question 2

Which metabolite cannot be directly converted from pyruvate?

a) Acetaldehyde
b) Acetyl CoA
c) Ethanol
d) Lactate

Answer 2

c) Ethanol

Question 3

Which step in glycolysis is reversible?

a) 1,3 bisphosphoglycerate + ADP –> 3-phosphoglycerate + ATP
b) Glucose + ATP –> glucose 6-phosphate + ADP
c) Fructose 6-phosphate + ATP –> fructose 1,6-bisphosphate + ADP
d) Phosphoenolpyruvate + ADP –> pyruvate + ATP

Answer 3

a) 1,3 bisphosphoglycerate + ADP  3-phosphoglycerate + ATP

Question 4

The overall reaction of GNG is:

a) Pyruvate + 2ATP + GTP + NADH –> Glucose
b) 2Pyruvate + 6ATP + 2NADH –> Glucose
c) Pyruvate + 3ATP + NADH –> Glucose
d) 2Pyruvate + 6ATP + NADH –> Glucose

Answer 4

b) 2Pyruvate + 6ATP + 2NADH –> Glucose

Question 5

What will happen to GNG if a starved person becomes drunk? (Challenging!)

a) Decrease entry of lactate into GNG because the lactate dehydrogenase reaction will be pushed towards the formation of lactate.
b) Increased entry of lactate into GNG because the lactate dehydrogenase reaction will be pushed towards the formation of pyruvate.
c) Decrease entry of lactate into GNG because the lactate dehydrogenase reaction will be pushed towards the formation of pyruvate.
d) Increased entry of lactate into GNG because the lactate dehydrogenase reaction will be pushed towards the formation of lactate.

Answer 5

a) Decrease entry of lactate into GNG because the lactate dehydrogenase reaction will be pushed towards the formation of lactate.

Question 6

Which molecule cannot be derived from pyruvate directly?

a) Lactate
b) Phosphoenolpyruvate
c) Alanine
d) Acetyl CoA

Answer 6

b) Phosphoenolpyruvate

Question 7

What are some the substrates (s) and products (P) of the TCA cycle?

a) S = Acetyl CoA, NADH, GDP; P = NAD+, GTP, CO2.
b) S = oxaloacetate, NAD+, GDP; P = NADH, GTP, and malate.
c) S = Acetyl-CoA, NAD+, GDP; P = NADH, GTP, CO2.
d) S = Acetyl CoA, NAD+, GTP; P = NADH, GDP, Oxaloacetate

Answer 7

c) S = Acetyl-CoA, NAD+, GDP; P = NADH, GTP, CO2.

Question 8

If you begin with a dihydroxyacetone phosphate (DHAP), how many ATP, NADH, FADH2, and CO2 do you end up with at the end of TCA cycle?

a) 3 CO2, 5 NADH, 3 ATP, and 1 FADH2
b) 2 CO2, 5 NADH, 2 ATP, and 1 FADH2
c) 3 CO2, 6 NADH, 5 ATP, and 1 FADH2
d) 2 CO2, 4 NADH, 3 ATP, and 1 FADH2

Answer 8

a) 3 CO2, 5 NADH, 3 ATP, and 1 FADH2

Question 9

If you start with one molecule of glucose, by the end of TCA cycle, how many ATP, NADH, FADH2 would you have produced?

a) 4 ATP, 8 NADH, 2 FADH2
b) 3 ATP, 7 NADH, 1 FADH2
c) 3 ATP, 5 NADH, 1 FADH2
d) 4 ATP, 10 NADH, 2 FADH2

Answer 9

d) 4 ATP, 10 NADH, 2 FADH2

Question 10

Theoretically, if fumarate is fed into mitochondria, how many ATP molecules should be produced by the end of electron transport chain?

a) 2.5
b) 1.5
c) 3
d) 5

Answer 10

2.5

Question 11

If the following half-reactions are combined, what is the reductional potential for the spontaneous reaction?

oxaloacetate- + 2H+ + 2e- –> malate- E= -0.166
NAD+ + H+ + 2e- –> NADH E= -0.315

a) -0.481 V
b) -0.149 V
c) 0.0523 V
d) 0.149 V

Answer 11

d) 0.149 V

Question 12

If alanine is fed to cells that are actively carrying out aerobic respiration, how many ATP molecules will cells produce at the end of electron transport chain?

a) 12.5
b) 25
c) 10.5
d) 13.5

Answer 12

a) 12.5

Question 13

If alanine is fed to cells in the presence of cyanide, how many ATP molecules will cells produce at the end of electron transport chain? Assuming no feedback inhibition.

a) 2.5
b) 1
c) 1.5
d) 0

Answer 13

b) 1

Question 14

Why was there a rise in body temperature in the individuals affected by DNP?

a) In the presence of DNP, pyrogen is produced to trigger fever.
b) In the presence of DNP, the activity of the mitochondria is increased in order to produce more ATP.
c) In the presence of DNP, the proton motive force is dissipated as heat.
d) In the presence of DNP, mitochondria are inhibited, resulting the increased rate of anaerobic respiration.

Answer 14

c) In the presence of DNP, the proton motive force is dissipated as heat.

Question 15

All of the following molecules play a role in carbohydrate metabolism, but one of them is also essential in fat catabolism. What is it?

a) Citrate
b) Pyruvate
c) Succinate
d) Acetyl CoA

Answer 15

d) Acetyl CoA

Question 16

How many ATP molecules are produced when C6:0 fatty acid is catabolized?

a) 40
b) 42
c) 38
d) 36

Answer 16

d) 36

Question 17

Why would diversifying the fat sources by including odd-chain fatty acids improve a person’s overall metabolic health? Assume this person is on a high fat diet, such as blubber.

a) Odd-chain fatty acids when broken down provide intermediates that can replenish the TCA cycle and glucoconeogenesis.
b) Odd-chain fatty acids provide less energy than the blubber fat, thus accelerating the clearance of the blubber fat in the person’s body.
c) Odd-chain fatty acids when broken down provide glycerol that can be used in glycolysis or gluconeogenesis.
d) Odd-chain fatty acids provide is rich in omega-3 fatty acids and vitamin D, which are lacking from blubber.

Answer 17

a) Odd-chain fatty acids when broken down provide intermediates that can replenish the TCA cycle and glucoconeogenesis.

Question 18

How many ATP molecules are produced when C5:0 fatty acid is catabolized? (Assuming succinyl CoA goes through TCA cycle)

a) 22
b) 24
c) 14
d) 16

Answer 18

d) 16

Question 19

What is the reason for liver’s inability to use ketone bodies?

a) Liver misses CoA transferase.
b) Liver misses 3-hydroxybutyrate dehydrogenase.
c) Liver misses ketothiolase.
d) Liver misses HMG-CoA reductase.

Answer 19

a) Liver misses CoA transferase.

Question 20

Which of the following is NOT a condition required for ketogenesis?

a) Prolonged fasting/starvation
b) Increased lipolysis and fatty acid oxidation
c) Insulin signaling
d) Depletion of oxaloacetate

Answer 20

c) Insulin signaling

Question 21

All of the following molecules play a role in carbohydrate metabolism, but one of them is also essential in fat acid synthesis. What is it?

a) Pyruvate
b) Acetoacetate
c) Citrate
d) Succinate

Answer 21

c) Citrate

Question 22

FADH2 is a common reducing factor that is reoxidized in ETC to produce ATP. Which enzyme does not produce FADH2?

a) Succinate dehydrogenase
b) Mitochondrial glycerol-3-phosphate dehydrogenase
c) Malic enzyme
d) Acyl-CoA dehydrogenase

Answer 22

c) Malic enzyme

Question 23

To synthesize C12:0 fatty acid, how many NADPH molecules are added?

a) 12
b) 14
c) 8
d) 10

Answer 23

d) 10

Question 24

Which of the following is not a component of the pentose phosphate pathway?

a) NADH
b) CO2
c) NADPH
d) Erythrose 4-phosphate

Answer 24

a) NADH

Question 25

In addition to pentose phosphate pathway, which other pathway produces NADPH for fatty acid synthesis?

a) Glycolysis
b) Malic enzyme involved in citrate shuttling
c) Citric acid cycle
d) Gluconeogenesis

Answer 25

b) Malic enzyme involved in citrate shuttling

Question 26

We have previously seen that cancer cells alter glucose metabolism to meet the needs of rapid cell growth. Cancer cells may also take advantage of fatty acid synthesis.

Which statement about the role of FAS in cancer is wrong:

a) FAS provides signaling molecules for cancer proliferation.
b) FAS provides substrates for protein acylation, which may promote cancer proliferation.
c) FAS provides structural molecules for cancer proliferation.
d) FAS provides intermediates for glucose and glycogen synthesis.

Answer 26

d) FAS provides intermediates for glucose and glycogen synthesis.

Question 27

Which of the following metabolites can be directly used to make alanine?

a) Lactate
b) Acetyl CoA
c) Oxaloacetate
d) Pyruvate

Answer 27

d) Pyruvate

Question 28

To synthesize a hexapeptide made of alanine, how many glucose molecules do you need?

a) 5
b) 3
c) 4
d) 6

Answer 28

b) 3

Question 29

During lecture 22 - gluconeogenesis, we mentioned that amino acids Leu and Lys cannot be used to make glucose. What is the reason?

a) Leu and Lys are too large.
b) Leu and Lys are broken down to acetoacetate.
c) Leu and Lys are hydrophobic amino acids.
d) Leu and Lys are essential amino acids.

Answer 29

b) Leu and Lys are broken down to acetoacetate.