Question

4. Using a series of arrows, draw the branched metabolic reaction pathway described by the following statements, and use the diagram to answer the questions.

Pyruvate can be converted to either Oxaloacetate or ActeylCoA.

AcetylCoA can be converted to Citrate.

Citrate can be converted to Ketoglutarate

Ketoglutarate can be converted to Glutamate or Succinate.

Glutamate can be converted to Glutamine.

Succinate can be converted to Fumarate.

The enzyme that converts Succinate to Fumarate requires Mg++

Glutamine is a competitive inhibitor of the enzyme that catalyzes reaction of Ketoglutarate to Glutamate.

Fumarate is a noncompetitive inhibitor of the enzyme that catalyzes the reaction of Pyruvate to AcetylCoA.



Explain the function of Mg++
When the concentration of fumarate is very high, explain what happens to the concentrations of Glutamine and Oxaloacetate?
Is this an example of feedback inhibition or allosteric regulation? Explain your answer. What other information might be needed to make a better answer?

Answer 1

Mg++ functions as a cofactor for the enzyme that converts Succinate to Fumarate. This means that the enzyme requires Mg++ in order to function properly and efficiently.


When the concentration of fumarate is very high, it can act as a noncompetitive inhibitor of the enzyme that catalyzes the reaction of Pyruvate to AcetylCoA. This means that the rate of this reaction will decrease, leading to a decrease in the concentration of AcetylCoA. Since AcetylCoA is a precursor for both Citrate and Ketoglutarate, their concentrations will also decrease. As a result, the concentration of Oxaloacetate, which is a precursor for Citrate, will increase due to the decrease in Citrate production. The concentration of Glutamine, which is produced from Glutamate, will also decrease since the production of Glutamate from Ketoglutarate will be reduced.


This is an example of allosteric regulation, as the inhibitors (fumarate and glutamine) bind to the enzyme at a site other than the active site and cause a conformational change that affects the enzyme's activity. However, more information is needed to determine whether it is also an example of feedback inhibition. Feedback inhibition occurs when a downstream product inhibits an earlier step in the pathway. In this case, we do not have enough information to determine whether the inhibitors (fumarate and glutamine) are downstream products or not.