Based on the animation, how many electron carriers are reduced during the Krebs cycle only?

• A. One NAD\(^+\) and three FAD are reduced per cycle
• B. Four NAD\(^+\) and no FAD are reduced per cycle
• C. Two NAD\(^+\) and two FAD are reduced per cycle
• D. Three NAD\(^+\) and one FAD are reduced per cycle

Answer: (D)

Verified step by step guidance

1. Step 1: Understand the Krebs cycle (also known as the citric acid cycle), which is a series of chemical reactions used by all aerobic organisms to generate energy through the oxidation of acetyl-CoA derived from carbohydrates, fats, and proteins.
2. Step 2: Recall that during the Krebs cycle, electron carriers such as NAD\(^+\) (Nicotinamide Adenine Dinucleotide) and FAD (Flavin Adenine Dinucleotide) are reduced to NADH and FADH\(_2\), respectively. These reduced carriers are essential for transferring electrons to the electron transport chain.
3. Step 3: Analyze the given options and note the number of NAD\(^+\) and FAD molecules reduced per cycle. The correct answer states that three NAD\(^+\) molecules and one FAD molecule are reduced during the Krebs cycle.
4. Step 4: Verify this information by reviewing the steps of the Krebs cycle. Specifically, NAD\(^+\) is reduced to NADH during three key reactions: (1) isocitrate to α-ketoglutarate, (2) α-ketoglutarate to succinyl-CoA, and (3) malate to oxaloacetate. FAD is reduced to FADH\(_2\) during the conversion of succinate to fumarate.
5. Step 5: Conclude that the correct answer is based on the biochemical reactions of the Krebs cycle, where three NAD\(^+\) molecules and one FAD molecule are reduced per cycle, providing electron carriers for subsequent energy production in the electron transport chain.