Since both glycolysis and gluconeogenesis are irreversible processes, there is no thermodynamic barrier to their simultaneous operation. However, it is important for the cell not to run both glycolysis and gluconeogenesis at high rates simultaneously. Which of the following is a reason for this?

a. More pyruvate is consumed in one round of gluconeogenesis than is produced in one round of glycolysis.

b. A net loss of 2 ATP would occur for each simultaneous round of glycolysis and gluconeogenesis.

c. A net loss of 4 ATP would occur for each simultaneous round of glycolysis and gluconeogenesis.

d. Both the first and second answers are correct.

e. Both the first and third answers are correct.

Answer:C

Explanation:

It is important for the cell not to activate glycolysis and gluconeogenesis at high rate simultaneously because it is expensive for the cell.

In the break down of one molecule of glucose to pyruvate, one ATP is used in the conversion of glucose to glucose-6-phosphate and one ATP is used in the conversion of fructose-1-phoshate to fructose-1,6-biphosohate. While a total of four ATPs are produced.

Making it a net gain of 2 ATP in glycolysis.

Gluconeogenesis produces no ATP and requires equivalents of 6 ATP (4 ATP and 2GTP) for one molecule of glucose produced.

(Glycolysis + 2ATP) + (gluconeogenesis - 6ATP) = - 4ATP

There's a net loss of 4ATP if both reactions are activated simultaneously.