Which are inputs to the citric acid cycle?

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Multiple Choice

Which are inputs to the citric acid cycle?

The citric acid cycle needs a two-carbon donor, coenzymes that carry electrons, and a substrate-level phosphorylation step to run. The two-carbon acetyl group from acetyl-CoA enters the cycle by combining with oxaloacetate to form citrate, providing the carbon skeleton the cycle oxidizes turn after turn. The cycle also requires NAD+ and FAD to act as electron acceptors as the intermediates are oxidized; they are reduced to NADH and FADH2 as the cycle proceeds. In addition, the step that generates energy at the substrate level uses GDP (or ADP in some organisms) and inorganic phosphate to form GTP (or ATP), depending on the tissue. Water is involved in some reactions, but there is no net consumption of water in the overall inputs, and CO2 is produced rather than consumed. So the essential inputs are acetyl-CoA, NAD+, GDP, and FAD, with acetyl-CoA providing the fuel, NAD+ and FAD accepting electrons, and GDP enabling the formation of GTP during the cycle.

The citric acid cycle needs a two-carbon donor, coenzymes that carry electrons, and a substrate-level phosphorylation step to run. The two-carbon acetyl group from acetyl-CoA enters the cycle by combining with oxaloacetate to form citrate, providing the carbon skeleton the cycle oxidizes turn after turn. The cycle also requires NAD+ and FAD to act as electron acceptors as the intermediates are oxidized; they are reduced to NADH and FADH2 as the cycle proceeds. In addition, the step that generates energy at the substrate level uses GDP (or ADP in some organisms) and inorganic phosphate to form GTP (or ATP), depending on the tissue. Water is involved in some reactions, but there is no net consumption of water in the overall inputs, and CO2 is produced rather than consumed.

So the essential inputs are acetyl-CoA, NAD+, GDP, and FAD, with acetyl-CoA providing the fuel, NAD+ and FAD accepting electrons, and GDP enabling the formation of GTP during the cycle.

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