Question

I would appreciate it if you may answer all questions, throughyly. Thank you These Probelms are regarding Citric Acid Cycle

5. In the conversion from citrate (which is not chiral) into isocitrate (which is chiral), the carbon from oxaloacetate is always the one oxidized, not the carbon from the acetate (delivered by acetyl-CoA). Explain how this happens.

6. In the third step of the cycle, the alcohol is oxidized into a carbonyl by isocitrate dehydrogenase. How does this step assist in eliminating the first CO2 from the molecule?

7. The fourth step of the cycle, the removal of the second CO2 from the molecule, resembles a multistep reaction earlier in the metabolic pathway. Identify this step, and list their similarities.

10. What is the purpose of the seventh and eighth steps of the cycle? The eighth step in particular has a high positive standard free energy change. How is the cycle assured to continue despite this?

11. Which steps of the citric acid cycle involve enzymes that are highly regulated? Why does it make sense that these steps are exergonic?

12.The two carbons in an acetyl-CoA are released as CO2 only in the second turn of the citric acid cycle. Explain why this is so.

13. Briefly describe the role of the citric acid cycle in anabolism, and the role of anaplerotic reactions with regard to the cycle.

Answer 1

5. In the conversion from citrate (which is not chiral) into isocitrate (which is chiral), the carbon from oxaloacetate is always the one oxidized, not the carbon from the acetate (delivered by acetyl-CoA). Explain how this happens.

In the second step of citric acid cycle, citrate is converted into its isomer, isocitrate. This is actually a two-step process, involving first the removal and then the addition of a water molecule. Acetyl - coA conveys the carbon atoms within the acetyl group to the citric acid cycle (Krebs cycle) to be oxidized for energy production.