Question

A lack of ATP (high ADP, AMP, Pi) would favor

a. Glycolysis over gluconeogenesis

b. Glycogenolysis over glycogenesis

c. Gluconeogenesis over glycolysis

d. Glycogenesis over glycogenolysis

e. Both a and b f. Both c and b

Please confirm if A is the correct answer.

Answer 1

Answer: a. Glycolysis over gluconeogenesis

If ATP conc was = AMP and Pi, then there would be no driving force. The equilibrium always favors low ATP (high ADP) concentration. However, the cell maintains [ATP] much higher than its equilibrium value. Thus a driving force for hydrolysis of ATP is always present. Since ATP is a source of energy and it is maintained out of equilibrium with its hydrolysis product ADP. If [ATP] were allowed to reach its equlibrium value, no free energy would be stored. When ATP / ADP ratio is low, the TCA cycle is turned on. An increase in ADP and the associated increase in AMP (due to the adenylate kinase equilibrium) will activate AMP deaminase and result in an increased formation of IMP and NH₃. Deamination of AMP will occur during conditions of elevated ADP and AMP and thus reduced ATP/ADP ratio. Deamination of AMP will remove AMP from the adenylate kinase reaction and resore ATP/ADP ratio.

A high level of AMP indicates that the energy charge is low and signals the need for ATP generation. gluconeogenesis is nearly switched off and glycolysis is promoted.

Conversely, high levels of ATP and citrate indicate that the energy charge is high and that biosynthetic intermediates are abundant. Under these conditions, glycolysis is nearly switched off and gluconeogenesis is promoted.

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