Final answer:
The key control points in the citric acid cycle are the enzymes citrate synthase and isocitrate dehydrogenase, which are subject to regulation by ATP levels, illustrating feedback inhibition and activation mechanisms.
Step-by-step explanation:
The key control points within the citric acid cycle, also known as the Krebs cycle or TCA cycle, are primarily regulated by the enzymes citrate synthase and isocitrate dehydrogenase. In step 1 of the cycle, citrate synthase catalyzes the condensation of acetyl CoA and oxaloacetate to form citrate, which is an irreversible reaction and highly exergonic. This step is regulated by the availability of ATP, displaying negative feedback when ATP levels are high, resulting in a decreased reaction rate. In contrast, when ATP is in short supply, the rate of this reaction increases. In step 3, isocitrate dehydrogenase catalyzes the oxidation of isocitrate to alpha-ketoglutarate, producing CO₂ and NADH. This step is also controlled by feedback from ATP and NADH and positively affected by ADP.