Q: Which of the following reactions is catalyzed by pyruvate carboxylase in gluconeogenesis?

$$\text{pyruvate} + \text{HCO}_3^- + \text{ATP} \rightarrow \text{oxaloacetate} + \text{ADP} + \text{P}_i$$

Question 1

Which of the following best describes the role of UDP-glucose in glycogen biosynthesis?

Accepted Answer

UDP-glucose donates glucose units to glycogen via the enzyme glycogen synthase.

Question 2

Which enzyme catalyzes the conversion of glucose-1-phosphate to glucose-6-phosphate during glycogen breakdown?

Accepted Answer

Phosphoglucomutase

Question 3

During fasting, which enzyme activity of the bifunctional enzyme controlling fructose-2,6-bisphosphate levels is favored, and which hormone is primarily responsible?

Accepted Answer

Phosphatase activity; glucagon

Question 4

Which of the following reactions is catalyzed by pyruvate carboxylase in gluconeogenesis?

Accepted Answer

$$	ext{pyruvate} + 	ext{HCO}_3^- + 	ext{ATP} ightarrow 	ext{oxaloacetate} + 	ext{ADP} + 	ext{P}_i$$

Question 5

Which metabolite directly connects glycolysis, gluconeogenesis, and the pentose phosphate pathway?

Accepted Answer

Glucose-6-phosphate

Question 6

What is the main function of NADPH produced in the oxidative phase of the pentose phosphate pathway?

Accepted Answer

To provide reducing power for biosynthetic reactions and protection against oxidative stress

Question 7

Which enzyme is responsible for the first committed and irreversible step of the pentose phosphate pathway?

Accepted Answer

Glucose-6-phosphate dehydrogenase

Question 8

How does high cellular AMP concentration affect glycolysis and gluconeogenesis?

Accepted Answer

Stimulates glycolysis and inhibits gluconeogenesis

Question 9

Which of the following best explains why the phosphorylated form of glycogen synthase is inactive?

Accepted Answer

Phosphorylation causes a conformational change that reduces its affinity for UDP-glucose.

Question 10

Which of the following is a product of the oxidative decarboxylation step in the pentose phosphate pathway?

Accepted Answer

Ribulose-5-phosphate, CO$$_2$$, and NADPH

Question 11

A patient with a deficiency in glucose-6-phosphate dehydrogenase is likely to experience which of the following symptoms under oxidative stress?

Accepted Answer

Increased susceptibility to hemolytic anemia due to reduced NADPH production

Question 12

Which of the following best describes the role of transketolase in the pentose phosphate pathway?

Accepted Answer

Transfers two-carbon units in the non-oxidative phase

Question 13

Which hormone promotes the dephosphorylation of the bifunctional enzyme, leading to increased levels of fructose-2,6-bisphosphate?

Accepted Answer

Insulin

Question 14

Which of the following is a direct substrate for glycogen phosphorylase during glycogenolysis?

Accepted Answer

Glycogen

Question 15

Which of the following best explains the reciprocal regulation of phosphofructokinase (PFK) and fructose-1,6-bisphosphatase (FBPase) by AMP?

Accepted Answer

AMP stimulates PFK and inhibits FBPase, promoting glycolysis and inhibiting gluconeogenesis.

Question 16

Which of the following best describes the fate of ribulose-5-phosphate in the non-oxidative phase of the pentose phosphate pathway?

Accepted Answer

It is converted to ribose-5-phosphate and intermediates of glycolysis.

Question 17

Which of the following best explains why gluconeogenesis is energetically expensive for the cell?

Accepted Answer

It requires the hydrolysis of multiple high-energy phosphate bonds (ATP and GTP) for each glucose synthesized.

Question 18

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

Accepted Answer

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

Question 19

A patient with a deficiency in biotin would have impaired activity of which gluconeogenic enzyme?

Accepted Answer

Pyruvate carboxylase

Question 20

Which of the following best describes the effect of glucagon on glycogen synthase?

Accepted Answer

Glucagon signaling leads to phosphorylation and inactivation of glycogen synthase.

Carbon Pathways: Glycogen Metabolism, Gluconeogenesis, and the Pentose Phosphate Pathway

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