Question 1

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

Accepted Answer

Catabolic pathways break down complex molecules into simpler ones, releasing energy, while anabolic pathways build complex molecules from simpler ones, consuming energy.

Question 2

Why is the hydrolysis of ATP to ADP and inorganic phosphate ($$\mathrm{ATP} + \mathrm{H}_2\mathrm{O} \rightarrow \mathrm{ADP} + \mathrm{P_i}) $$considered a favorable reaction in cells?

Accepted Answer

Because it has a large negative standard free energy change ($$\Delta G^\circ$$), primarily due to relief of electrostatic repulsion and increased resonance stabilization of products.

Question 3

Despite being thermodynamically favorable, ATP is not spontaneously hydrolyzed in the cell. What is the main reason for this?

Accepted Answer

ATP hydrolysis requires a specific enzyme to lower the activation energy barrier.

Question 4

A reaction with a positive $$\Delta G$$ can be driven forward in the cell by coupling it to ATP hydrolysis. If reaction A has $$\Delta G = +15\ \mathrm{kJ/mol}$$ and ATP hydrolysis has $$\Delta G = -30\ \mathrm{kJ/mol}$$, what is the overall $$\Delta G$$ for the coupled process?

Accepted Answer

$$-15\ \mathrm{kJ/mol}$$

Question 5

Which of the following is a physiological role of NAD+ in glycolysis?

Accepted Answer

It serves as an electron acceptor, becoming reduced to NADH during the oxidation of glyceraldehyde-3-phosphate.

Question 6

Under anaerobic conditions in muscle cells, what happens to the pyruvate and NADH produced during glycolysis?

Accepted Answer

Pyruvate is converted to lactate, regenerating NAD+ from NADH.

Question 7

Which enzyme catalyzes the first substrate-level phosphorylation in glycolysis, and what is the product?

Accepted Answer

Phosphoglycerate kinase; 3-phosphoglycerate

Question 8

How many net ATP molecules are produced per molecule of glucose during glycolysis via substrate-level phosphorylation?

Accepted Answer

2

Question 9

Which of the following best explains the dual role of glycolysis in cells?

Accepted Answer

It provides both energy (ATP) and metabolic intermediates for biosynthetic pathways.

Question 10

Which enzyme is the primary regulatory point of glycolysis and is allosterically inhibited by high levels of ATP?

Accepted Answer

Phosphofructokinase-1 (PFK-1)

Question 11

A patient with hereditary fructose intolerance lacks aldolase B. What is the physiological consequence of this deficiency?

Accepted Answer

Accumulation of fructose-1-phosphate in the liver, leading to hypoglycemia and liver damage.

Question 12

Which of the following is NOT a precursor for gluconeogenesis in humans?

Accepted Answer

Fatty acids

Question 13

Why can't fatty acids serve as precursors for gluconeogenesis in humans?

Accepted Answer

The conversion of fatty acids to acetyl-CoA is irreversible, and acetyl-CoA cannot be converted back to pyruvate or oxaloacetate in animals.

Question 14

Which of the following steps in gluconeogenesis bypasses the irreversible pyruvate kinase reaction of glycolysis?

Accepted Answer

Pyruvate carboxylase and phosphoenolpyruvate carboxykinase (PEPCK) convert pyruvate to phosphoenolpyruvate.

Question 15

What is the energetic cost (in terms of high-energy phosphate bonds) to synthesize one molecule of glucose from two molecules of pyruvate via gluconeogenesis?

Accepted Answer

4 ATP, 2 GTP, and 2 NADH

Question 16

Which vitamin is required as a cofactor for pyruvate carboxylase in gluconeogenesis?

Accepted Answer

Biotin

Question 17

Which hormone stimulates gluconeogenesis in the liver during fasting?

Accepted Answer

Glucagon

Question 18

Which of the following is a key product of the oxidative branch of the pentose phosphate pathway?

Accepted Answer

NADPH

Question 19

A deficiency in glucose-6-phosphate dehydrogenase (G6PDH) can lead to hemolytic anemia. What is the biochemical basis for this disease?

Accepted Answer

Decreased NADPH production impairs the regeneration of reduced glutathione, making red blood cells more susceptible to oxidative damage.

Question 20

Which enzyme is the primary regulatory point of the pentose phosphate pathway, and how is it regulated?

Accepted Answer

Glucose-6-phosphate dehydrogenase; inhibited by high levels of NADPH

Carbohydrate Metabolism: Catabolism, Anabolism, Glycolysis, Gluconeogenesis, and the Pentose Phosphate Pathway

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