Q: Calculate the thermodynamic efficiency of anaerobic glycolysis if the energy conserved in ATP is $$61.0 \, \mathrm{kJ} \, \mathrm{mol}^{-1}$$ and the total energy released is $$184.6 \, \mathrm{kJ} \, \mathrm{mol}^{-1}.$$

$$\frac{61.0}{184.6} \times 100 \approx 33\%$$

Question 1

Why is the regeneration of NAD⁺ essential for glycolysis under anaerobic conditions?

Accepted Answer

NAD⁺ is required as an electron acceptor in the glyceraldehyde-3-phosphate dehydrogenase reaction, allowing glycolysis to continue.

Question 2

Which enzyme catalyzes the reduction of pyruvate to lactate in anaerobic glycolysis?

Accepted Answer

Lactate dehydrogenase

Question 3

What is the main metabolic function of fermentation in anaerobic cells?

Accepted Answer

Regeneration of NAD⁺ to allow glycolysis to continue

Question 4

Which of the following best describes the fate of lactate produced in skeletal muscle during intense exercise?

Accepted Answer

It is transported to the liver, converted back to pyruvate, and used for gluconeogenesis.

Question 5

Which LDH isozyme is predominant in heart tissue, and what is its main substrate preference?

Accepted Answer

LDH 1 (H₄); prefers lactate as a substrate

Question 6

Which coenzyme is required by pyruvate decarboxylase during alcoholic fermentation?

Accepted Answer

Thiamine pyrophosphate (TPP)

Question 7

What is the net ATP yield per molecule of glucose during anaerobic glycolysis?

Accepted Answer

$$2 \, \mathrm{ATP}$$

Question 8

Which reaction in glycolysis is directly responsible for the reduction of NAD⁺ to NADH?

Accepted Answer

Glyceraldehyde-3-phosphate + P_i + NAD⁺ → 1,3-Bisphosphoglycerate + NADH + H⁺

Question 9

Which of the following best explains why glycolysis can proceed even if some steps are endergonic under standard conditions?

Accepted Answer

The overall pathway is exergonic, and product removal and enzyme coupling drive less favorable reactions forward.

Question 10

Calculate the thermodynamic efficiency of anaerobic glycolysis if the energy conserved in ATP is $$61.0 \, \mathrm{kJ} \, \mathrm{mol}^{-1}$$ and the total energy released is $$184.6 \, \mathrm{kJ} \, \mathrm{mol}^{-1}.$$

Accepted Answer

$$\frac{61.0}{184.6} 	imes 100 \approx 33\%$$

Question 11

Which of the following is a key difference between lactate fermentation and alcoholic fermentation?

Accepted Answer

Alcoholic fermentation produces carbon dioxide, while lactate fermentation does not.

Question 12

Which of the following best describes the role of TPP in the pyruvate decarboxylase reaction?

Accepted Answer

It forms a carbanion that attacks pyruvate, stabilizing the two-carbon intermediate after decarboxylation.

Question 13

Which of the following is a clinical consequence of anaerobic metabolism by oral bacteria in dental plaque?

Accepted Answer

Acidic metabolic products lower pH and damage tooth enamel, leading to cavities.

Question 14

What is the net equation for alcoholic fermentation, including glycolysis and fermentation steps?

Accepted Answer

$$\mathrm{Glucose} + 2\mathrm{ADP} + 2\mathrm{P}_i + 2\mathrm{H}^+ \rightarrow 2\mathrm{Ethanol} + 2\mathrm{ATP} + 2\mathrm{CO}_2 + 2\mathrm{H}_2O$$

Question 15

Which of the following statements about the ATP balance in glycolysis is correct?

Accepted Answer

Two ATP are consumed in the preparatory phase, and four ATP are produced in the payoff phase, resulting in a net gain of two ATP per glucose.

Question 16

Which of the following best explains why the standard free-energy change ($$\Delta G$$^{\circ\prime}$$) for glycolysis is less negative when ATP is produced?

Accepted Answer

Some of the energy released from glucose breakdown is conserved in ATP rather than dissipated as heat.

Question 17

Which of the following is true regarding the recycling of NAD⁺ and NADH in fermentation?

Accepted Answer

NAD⁺ is reduced to NADH during glycolysis and regenerated from NADH during fermentation, maintaining redox balance.

Question 18

Which of the following best describes the fate of acetaldehyde in alcoholic fermentation?

Accepted Answer

It is reduced to ethanol by alcohol dehydrogenase, regenerating NAD⁺.

Anaerobic Metabolism and Energy Production in Glycolysis: Study Notes

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