Question

In the Krebs cycle, the enzyme isocitrate dehydrogenase (IDH) is allosterically activated by ADP at high concentrations. How does this interaction regulate the Krebs cycle?

A) It inhibits the conversion of isocitrate to α-ketoglutarate.
B) It accelerates the conversion of citrate to isocitrate.
C) It enhances the conversion of isocitrate to α-ketoglutarate.
D) It converts α-ketoglutarate to isocitrate.

Answer 1

ADP activates isocitrate dehydrogenase in the Krebs cycle to enhance the conversion of isocitrate to α-ketoglutarate, thereby regulating the cycle's speed in response to the cell's energy needs.

Step-by-step explanation:

The interaction of ADP with isocitrate dehydrogenase (IDH) regulates the Krebs cycle by providing feedback about the energy status of the cell. When ADP concentrations are high, this signals that more ATP needs to be produced. As a result, IDH is allosterically activated by ADP, which enhances the conversion of isocitrate to α-ketoglutarate, leading to an increased rate of the Krebs cycle. This process ensures that when the cell's energy levels are low (high ADP levels), the cycle speeds up to produce more ATP. When ATP and NADH levels are adequate, signaling that the cell has sufficient energy, the rates of reactions catalyzed by enzymes like IDH decrease.