Question

Which of the following is a key control enzyme in the regulation of respiration?

a. Phosphofructokinase

b. Pyruvate Dehyrogenase

c. Citrate synthase

d. All of the above

e. None of the above

Answer 1

D, All of the above

Cellular respiration occurs in three stages- glycolysis, Krebs cycle and oxidative phosphorylation. each stage has control enzymes with allosteric effects which is like an ON/OFF switch for the entire process.

A, Phosphofructokinase is an important control enzyme for the third step in glycolysis.

Activated or stimulated by presence of ADP or AMP

Inhibited by presence of ATP, citrate

Since the motive of respiration is to produce ATP, if the cell has sufficient ATP molecules, then phosphofructokinase OFF s the glycolysis pathway. So this is one strategic control.

B, Pyruvate dehydrogenase

It is a complex of Enzymes required to convert pyruvate into acetyl co-A. Only then the molecule can enter TCA cycle.

High levels of NADH inhibits Pyruvate dehydrogenase function through feedback inhibition.

C, Citrate synthase

It is an enzyme which plays its role in the TCA cycle.

Feed back inhibition- if the product citrate is present, then the enzyme is inhibited by feed back inhibition.

So all these key enzymes are important for controlling cellular respiration