Question 1

Which of the following best describes the role of a second messenger in a G-protein coupled receptor (GPCR) signaling pathway?

Accepted Answer

It transmits the signal from the cell surface receptor to intracellular targets, amplifying the response.

Question 2

A patient is given a drug that irreversibly inhibits phosphodiesterase in liver cells. What is the most likely immediate effect on the G-protein signaling pathway?

Accepted Answer

Accumulation of cAMP, resulting in prolonged activation of downstream effectors.

Question 3

Which of the following best explains why ATP hydrolysis is commonly used to drive energetically unfavorable reactions in metabolism?

Accepted Answer

ATP hydrolysis releases a large amount of free energy ($$\Delta G^\circ' \u003c 0$$), which can be coupled to unfavorable reactions.

Question 4

Which enzyme catalyzes the rate-limiting step of glycolysis, and what is the key metabolite that regulates its activity?

Accepted Answer

Phosphofructokinase-1 (PFK-1); regulated by fructose-2,6-bisphosphate (F2,6BP)

Question 5

Which of the following statements about the pentose phosphate pathway (PPP) is CORRECT?

Accepted Answer

The oxidative arm of the PPP generates NADPH and ribose-5-phosphate.

Question 6

Which of the following best describes the fate of pyruvate under anaerobic conditions in muscle cells?

Accepted Answer

Pyruvate is converted to lactate to regenerate NAD$$^+$$ for glycolysis.

Question 7

Which of the following is a key difference between NADH and NADPH in cellular metabolism?

Accepted Answer

NADH is primarily used in catabolic reactions for ATP production, while NADPH is used in anabolic reactions for biosynthesis.

Question 8

Which of the following best explains why separate enzymes are required for the irreversible steps of glycolysis and gluconeogenesis?

Accepted Answer

The irreversible steps of glycolysis have large negative $$\Delta G$$ values, so different enzymes are needed to catalyze the reverse reactions in gluconeogenesis.

Question 9

A patient with diabetes is treated with metformin. Which of the following best describes the mechanism of action of metformin?

Accepted Answer

It inhibits hepatic gluconeogenesis, decreasing glucose production in the liver.

Question 10

Which of the following statements about the TCA cycle is TRUE?

Accepted Answer

The TCA cycle is amphibolic, serving both catabolic and anabolic functions.

Question 11

Which of the following best describes the role of the malate-aspartate shuttle?

Accepted Answer

It transfers reducing equivalents (NADH) from the cytoplasm into the mitochondria for oxidative phosphorylation.

Question 12

Which of the following is the correct classification for the enzyme pyruvate kinase?

Accepted Answer

Transferase

Question 13

Which of the following best explains why glucose must be activated to UDP-glucose before being added to glycogen?

Accepted Answer

Activation to UDP-glucose provides the necessary energy and specificity for glycogen synthase to add glucose units to the growing polymer.

Question 14

Which of the following best describes the effect of insulin on glycolysis in liver cells?

Accepted Answer

Insulin increases the activity of phosphofructokinase-2 (PFK2), raising F2,6BP levels and stimulating glycolysis.

Question 15

Which of the following is a direct consequence of lactate accumulation in the blood during metformin-induced lactic acidosis?

Accepted Answer

Decreased blood pH due to increased proton concentration ($$[H^+]$$), leading to metabolic acidosis.

Question 16

Which of the following best describes the role of phosphorolysis in glycogen degradation?

Accepted Answer

It cleaves glucose units from glycogen by adding inorganic phosphate, producing glucose-1-phosphate.

Question 17

Which of the following is a key regulatory feature of the TCA cycle that ensures unidirectional (clockwise) flux?

Accepted Answer

Large negative $$\Delta G$$ values at key steps catalyzed by citrate synthase, isocitrate dehydrogenase, and $$\alpha-$$ketoglutarate dehydrogenase.

Question 18

Which of the following best describes an anaplerotic reaction in the context of the TCA cycle?

Accepted Answer

A reaction that replenishes TCA cycle intermediates, such as the conversion of pyruvate to oxaloacetate by pyruvate carboxylase.

Question 19

Which of the following best explains why the malate dehydrogenase reaction in the TCA cycle proceeds in the forward direction despite a positive standard free energy change ($$\Delta G^\circ' \u003e 0$$)?

Accepted Answer

The rapid consumption of oxaloacetate by citrate synthase pulls the reaction forward by maintaining a low oxaloacetate concentration.

Question 20

Which of the following is a correct statement about the connection between glycolysis and the pentose phosphate pathway (PPP)?

Accepted Answer

Glucose-6-phosphate can enter either glycolysis or the PPP, allowing cells to balance energy production and biosynthesis.

Biochemistry Study Guide: Biosignaling, Metabolism, Glycolysis, Gluconeogenesis, PPP, TCA Cycle, and Metformin Case Study

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