Question

Which of the following is the best hypothesis as to why the activity of pyruvate dehydrogenase is so tightly controlled by the cell? Note that many of these statements may be true about pyruvate dehydrogenase, but only one gives the best explanation for why the cell so tightly controls the activity of this enzyme.

Choose one:

A. Tight control of pyruvate dehydrogenase activity is needed so that pyruvate dehydrogenase can catalyze the reactions that produce acetyl-CoA, which enters the citrate cycle in order to provide ATP as a cellular energy source.

B. Tight control of pyruvate dehydrogenase activity is needed in order to coordinate the energy needs of the cell with the production of acetyl-CoA.

C. Tight control of pyruvate dehydrogenase activity is needed because the enzyme is readily regulated both by allosteric effectors and by covalent modification.

D. Tight control of pyruvate dehydrogenase activity is needed so that people do not develop vitamin deficiency diseases such as pellagra and beriberi.

Answer 1

The best hypothesis for the tight regulation of pyruvate dehydrogenase is to synchronize the cell's energy requirements with the production of acetyl-CoA, ensuring efficient energy usage and maintaining cellular homeostasis. The correct answer is option b.

Step-by-step explanation:

The best hypothesis as to why the activity of pyruvate dehydrogenase is so tightly controlled by the cell is to coordinate the energy production with the energy needs of the cell. Pyruvate dehydrogenase is a crucial enzyme in the metabolic pathway that converts pyruvate to acetyl-CoA, which enters the citric acid cycle (also known as the Krebs cycle or TCA cycle). This cycle is a key component in the cell's metabolic pathway for generating ATP, which is the main energy currency within cells.

Regulation occurs through multiple mechanisms, including allosteric effects by which the accumulation of products such as acetyl groups or NADH signals sufficient energy levels and slows the enzyme's activity. Additionally, tight regulation is achieved through covalent modifications such as phosphorylation; a kinase inactivates pyruvate dehydrogenase through phosphorylation, and a phosphatase reactivates it, with both the kinase and phosphatase themselves also subject to regulation.

This balance ensures that acetyl-CoA is produced in alignment with the cell's ATP needs, preventing energy waste and maintaining homeostasis. Therefore, the correct option is B: Tight control of pyruvate dehydrogenase activity is needed in order to coordinate the energy needs of the cell with the production of acetyl-CoA.