Question

Identify two places in the Krebs cycle where a decrease occurs.

a) Citrate synthase
b) Isocitrate dehydrogenase
c) Succinyl-CoA synthetase
d) Malate dehydrogenase

Answer 1

In the Krebs cycle, decreases can occur at isocitrate dehydrogenase and α-ketoglutarate dehydrogenase steps, especially when ATP and NADH levels are high, indicating these are control points for energy production regulation.

Step-by-step explanation:

The control of the Krebs cycle occurs at several points, primarily where NADH is produced. Two enzymes that catalyze these steps are isocitrate dehydrogenase and α-ketoglutarate dehydrogenase. The rate of these reactions decreases when levels of ATP and NADH are sufficient, but increases when more ATP is needed.

Regarding the question, isocitrate dehydrogenase, which converts isocitrate into α-ketoglutarate, and α-ketoglutarate dehydrogenase, which catalyzes the conversion of α-ketoglutarate into succinyl-CoA, are two places where a decrease occurs in the Krebs cycle. These steps can contribute to the regulation of energy production based on the cell’s ATP and NADH demand.