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 mutation in the gene encoding phosphodiesterase leads to its inactivation. What is the most likely cellular consequence?

Accepted Answer

Prolonged activation of signaling pathways due to accumulation of second messengers.

Question 3

Which of the following is the correct order of events in a typical G-protein signaling mechanism?

Accepted Answer

Ligand binds receptor → G-protein exchanges GDP for GTP → Effector activated → Second messenger produced

Question 4

Which of the following best describes the difference between catabolic and anabolic pathways?

Accepted Answer

Catabolic pathways break down molecules to produce ATP and CO$$_2$$, while anabolic pathways use ATP to synthesize complex molecules.

Question 5

Which enzyme class is responsible for transferring a phosphate group from ATP to glucose in the first step of glycolysis?

Accepted Answer

Transferase

Question 6

How does the pentose phosphate pathway (PPP) connect to nucleotide biosynthesis?

Accepted Answer

By producing ribose-5-phosphate, a precursor for nucleotide synthesis.

Question 7

Which of the following statements about NAD$$^+/$$NADH and NADP$$^+/$$NADPH is correct?

Accepted Answer

NAD$$^+/$$NADH is mainly involved in catabolic pathways, while NADP$$^+/$$NADPH is used in biosynthetic (anabolic) pathways.

Question 8

Which of the following best explains why ATP hydrolysis is often coupled to energetically unfavorable reactions?

Accepted Answer

The large negative free energy change ($$\Delta G) $$from ATP hydrolysis can drive unfavorable reactions forward.

Question 9

Which step in glycolysis is considered the rate-limiting step and is highly regulated?

Accepted Answer

Phosphofructokinase-1 (PFK-1) catalyzed conversion of fructose-6-phosphate to fructose-1,6-bisphosphate.

Question 10

What is the net ATP yield from glycolysis when starting from one molecule of glucose derived from glycogen (not free glucose)?

Accepted Answer

$$3$$ ATP

Question 11

Which tissue is primarily responsible for generating glucose from amino acids, triacylglycerols (TAG), and glycogen during fasting?

Accepted Answer

Liver

Question 12

Why are two enzymes required to convert pyruvate to phosphoenolpyruvate (PEP) in gluconeogenesis?

Accepted Answer

Because the direct reverse of pyruvate kinase is energetically unfavorable and requires bypass reactions.

Question 13

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

Accepted Answer

It donates glucose residues for elongation of the glycogen chain.

Question 14

Which of the following is a key difference between the oxidative and non-oxidative arms of the pentose phosphate pathway (PPP)?

Accepted Answer

The oxidative arm generates NADPH and ribulose-5-phosphate, while the non-oxidative arm interconverts sugars without producing NADPH.

Question 15

Which of the following best describes anaplerotic reactions in the TCA cycle?

Accepted Answer

Reactions that replenish TCA cycle intermediates to maintain cycle function.

Question 16

What is the primary energetic advantage of the thioester bond in acetyl-CoA during the TCA cycle?

Accepted Answer

It provides a high-energy bond that facilitates the transfer of the acetyl group to oxaloacetate.

Question 17

Which shuttle system is responsible for transferring reducing equivalents from cytosolic NADH into the mitochondria for oxidative phosphorylation?

Accepted Answer

Malate-aspartate shuttle

Question 18

In the context of diabetes treatment, what is the primary mechanism of action of metformin?

Accepted Answer

It inhibits hepatic gluconeogenesis, reducing glucose output by the liver.

Question 19

A patient with diabetes is treated with metformin but develops lactic acidosis. Which metabolic process is most directly affected, and what is the consequence for blood buffering?

Accepted Answer

Gluconeogenesis is inhibited, causing lactate accumulation and decreased blood pH.

Comprehensive Study Guide: Biosignaling, Metabolism, and the TCA Cycle

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