Counting reduced coenzymes from complete aerobic oxidation of one glucose In standard bacterial aerobic respiration (glycolysis + pyruvate dehydrogenase + tricarboxylic acid cycle), how many reduced coenzymes in total are generated per glucose and subsequently need to be reoxidized by the electron transport chain?

Introduction / Context:
Cellular respiration couples catabolism to ATP synthesis by harvesting electrons onto reduced coenzymes that must be reoxidized via the electron transport chain. Accounting for these reduced carriers per glucose clarifies bioenergetics, ATP yield, and the role of oxidative phosphorylation.

Given Data / Assumptions:

• Pathway sequence: glycolysis → pyruvate dehydrogenase (PDH) → tricarboxylic acid (TCA) cycle.
• Organism: a typical aerobic prokaryote with complete pathways.
• Reduced coenzymes counted: NADH and FADH2.

Concept / Approach:
Sum the reduced coenzymes produced in each stage per glucose. Glycolysis reduces NAD+ to NADH. PDH reduces NAD+ during oxidative decarboxylation of pyruvate. The TCA cycle reduces both NAD+ and FAD. Add the totals across stages; these carriers must be reoxidized to sustain flux.

Step-by-Step Solution:
Glycolysis: 2 NADH per glucose.PDH (two pyruvate → two acetyl-CoA): 2 NADH per glucose.TCA cycle (two acetyl-CoA): 6 NADH + 2 FADH2 per glucose.Total reduced coenzymes = 2 + 2 + 6 + 2 = 12.These 12 (10 NADH + 2 FADH2) feed electrons to the respiratory chain.

Verification / Alternative check:
Cross-check ATP equivalents: in many textbooks, prokaryotic yields are estimated from reoxidation of 10 NADH and 2 FADH2, consistent with 12 reduced carriers.

Why Other Options Are Wrong:

• 8 or 6 or 4: underestimate by omitting one or more pathway segments.
• 10: counts NADH only, ignores FADH2.

Common Pitfalls:
Forgetting that two turns of the TCA cycle occur per glucose and neglecting PDH-generated NADH.

Final Answer:
12