Q: Which of the following reactions is catalyzed by an enzyme that is present in the liver but absent in muscle and brain, thus allowing gluconeogenesis to be completed only in certain tissues?

$$\text{Glucose-6-phosphate} + \text{H}_2\text{O} \rightarrow \text{Glucose} + \text{P}_i$$

Question 1

Which enzyme catalyzes the conversion of pyruvate to oxaloacetate in gluconeogenesis, and what coenzyme is required for this reaction?

Accepted Answer

Pyruvate carboxylase; requires biotin as a coenzyme

Question 2

During vigorous exercise, muscle cells convert pyruvate to lactate. What is the primary purpose of this conversion?

Accepted Answer

To regenerate NAD$$^+$$ for glycolysis to continue under anaerobic conditions

Question 3

Which of the following reactions is catalyzed by an enzyme that is present in the liver but absent in muscle and brain, thus allowing gluconeogenesis to be completed only in certain tissues?

Accepted Answer

$$	ext{Glucose-6-phosphate} + 	ext{H}_2	ext{O} ightarrow 	ext{Glucose} + 	ext{P}_i$$

Question 4

Which of the following best explains why gluconeogenesis is not simply the reverse of glycolysis?

Accepted Answer

Glycolysis is highly exergonic overall, so the reverse pathway would be endergonic and not spontaneous

Question 5

Which molecule acts as an allosteric activator of pyruvate carboxylase, signaling a high-energy state and promoting gluconeogenesis?

Accepted Answer

Acetyl-CoA

Question 6

In the Cori cycle, what is the fate of lactate produced in muscle during anaerobic glycolysis?

Accepted Answer

It is transported to the liver, converted back to pyruvate, and then to glucose

Question 7

Which enzyme catalyzes the conversion of oxaloacetate to phosphoenolpyruvate in gluconeogenesis, and what nucleotide triphosphate is consumed in this reaction?

Accepted Answer

Phosphoenolpyruvate carboxykinase; GTP

Question 8

Which of the following statements about the regulation of glycolysis and gluconeogenesis is correct?

Accepted Answer

When glycolysis is active, gluconeogenesis is inhibited, and vice versa, to prevent a futile cycle

Question 9

Which of the following is a key regulatory enzyme in glycolysis that is replaced by a different enzyme in gluconeogenesis?

Accepted Answer

Phosphofructokinase (PFK-1) is replaced by fructose-1,6-bisphosphatase

Question 10

Which vitamin is required as a coenzyme for carboxylation reactions in gluconeogenesis, and what is its biochemical role?

Accepted Answer

Biotin; acts as a carrier of activated CO$$_2$$

Question 11

Which of the following best describes the thermodynamic feasibility of gluconeogenesis?

Accepted Answer

It is made exergonic by coupling to the hydrolysis of 4 ATP and 2 GTP per glucose synthesized

Question 12

Which of the following is a correct statement about the fate of NADH produced during glycolysis under anaerobic conditions in muscle?

Accepted Answer

NADH is oxidized by lactate dehydrogenase, regenerating NAD$$^+$$

Question 13

Which of the following best explains why fat catabolism cannot generate glucose?

Accepted Answer

Fatty acid breakdown yields acetyl-CoA, which cannot be converted to glucose in animals

Question 14

Which of the following is a regulatory effect of fructose-2,6-bisphosphate in liver cells?

Accepted Answer

It activates phosphofructokinase-1 and inhibits fructose-1,6-bisphosphatase

Question 15

Which of the following steps in gluconeogenesis occurs in the endoplasmic reticulum?

Accepted Answer

Conversion of glucose-6-phosphate to glucose by glucose-6-phosphatase

Question 16

Which of the following best describes the transport of oxaloacetate from the mitochondria to the cytosol during gluconeogenesis?

Accepted Answer

Oxaloacetate is reduced to malate, transported to the cytosol, and then oxidized back to oxaloacetate

Question 17

Which of the following is a correct equation for the reaction catalyzed by lactate dehydrogenase?

Accepted Answer

$$	ext{Pyruvate} + 	ext{NADH} + 	ext{H}^+ ightarrow 	ext{Lactate} + 	ext{NAD}^+$$

Question 18

Which of the following best describes the role of ATP in the regulation of glycolysis and gluconeogenesis?

Accepted Answer

High ATP inhibits glycolysis and activates gluconeogenesis

LEC 19 Glycolysis, Fermentation, and Gluconeogenesis: Pathways and Regulation

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