Which of the following molecules is a direct product of the Krebs cycle?

• A. NADH
• B. Pyruvate
• C. Lactate
• D. Glucose

Answer: (A)

Verified step by step guidance

1. Understand the context: The Krebs cycle (also known as the citric acid cycle or TCA cycle) is a series of chemical reactions that occur in the mitochondria of eukaryotic cells. It plays a central role in cellular respiration by oxidizing acetyl-CoA to produce energy-rich molecules.
2. Identify the main products of the Krebs cycle: The direct products of the Krebs cycle include NADH, FADH₂, ATP (or GTP), and CO₂. These molecules are generated as intermediates are oxidized and energy is captured.
3. Analyze the options: Review each option to determine if it is a direct product of the Krebs cycle. For example, NADH is a high-energy electron carrier produced during the cycle, while pyruvate is a product of glycolysis, lactate is a product of anaerobic respiration, and glucose is a substrate for glycolysis, not a product of the Krebs cycle.
4. Focus on NADH: During the Krebs cycle, NAD⁺ is reduced to NADH in multiple steps, such as during the conversion of isocitrate to α-ketoglutarate and α-ketoglutarate to succinyl-CoA. This makes NADH a direct product of the cycle.
5. Conclude: Based on the analysis, NADH is the correct answer as it is directly produced during the Krebs cycle, unlike the other options which are not products of this specific metabolic pathway.