The reduced coenzyme NADH produced in glycolysis in the cytoplasm reaches the electron transport chain by
Correct answer: B. being carried in by shuttle systems that transfer its electrons
- A. diffusing freely through both mitochondrial membranes
- B. being carried in by shuttle systems that transfer its electrons
- C. being converted into FADH2 first
- D. being broken down and never entering the mitochondrion
Explanation
The inner mitochondrial membrane is impermeable to NADH itself, so shuttle mechanisms transfer its electrons inside, sometimes at the cost of some ATP. This is why estimates of the total ATP yield vary between 36 and 38 per glucose.
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About Cellular Respiration
Cellular respiration releases energy from glucose through glycolysis, the link reaction, the Krebs cycle and the electron transport chain, producing ATP. The pathway differs in oxygen availability: aerobic respiration uses oxygen and yields more ATP, while anaerobic respiration produces much less ATP and forms lactic acid in muscles or ethanol and carbon dioxide in yeast.
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