Name a key regulator of the TCA cycle and describe how its activity is modulated by energy state.

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Multiple Choice

Name a key regulator of the TCA cycle and describe how its activity is modulated by energy state.

The main idea is that the TCA cycle is tuned by the cell’s energy state through allosteric regulation of key enzymes. A central control point is isocitrate dehydrogenase, which sits at a regulatory bottleneck in the cycle. When energy is required, ADP levels rise and activate this enzyme, speeding up the cycle to produce more NADH and FADH2 for the electron transport chain. When energy is abundant, high NADH and ATP levels inhibit isocitrate dehydrogenase, slowing flux through the cycle and preventing unnecessary production of reducing equivalents. Citrate synthase, while important, is not primarily activated by ADP and is inhibited by NADH and succinyl-CoA, not by ADP. Alpha-ketoglutarate dehydrogenase is inhibited by NADH (not activated) and is sensitive to other signals like Ca2+ in some tissues. Succinate dehydrogenase is more tightly tied to the ETC than to direct energy-state control, so it isn’t the principal regulator in response to cellular energy levels.

The main idea is that the TCA cycle is tuned by the cell’s energy state through allosteric regulation of key enzymes. A central control point is isocitrate dehydrogenase, which sits at a regulatory bottleneck in the cycle. When energy is required, ADP levels rise and activate this enzyme, speeding up the cycle to produce more NADH and FADH2 for the electron transport chain. When energy is abundant, high NADH and ATP levels inhibit isocitrate dehydrogenase, slowing flux through the cycle and preventing unnecessary production of reducing equivalents.

Citrate synthase, while important, is not primarily activated by ADP and is inhibited by NADH and succinyl-CoA, not by ADP. Alpha-ketoglutarate dehydrogenase is inhibited by NADH (not activated) and is sensitive to other signals like Ca2+ in some tissues. Succinate dehydrogenase is more tightly tied to the ETC than to direct energy-state control, so it isn’t the principal regulator in response to cellular energy levels.

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