Question

Why are these reactions for gluconeogenesis exergonic?
I get that Glucose 6-phosphate -> glucose and fructose 1,6-biphosphate -> fructose 6 phosphate release Pi, but doesn't the formation of formation of oxaloacetate and phosphoenolpyruvate require energy ( ATP and GTP)

ruvate. CH,OH CHOPO; HO он glucose 6- phosphatase HO OH OH 94 Он glucose 6-phosphate glucose glycolysao OPOH COCHZOPO HO O HO OH fructose 1,6- bisphosphatase ,POH COCH,OH HO он OH fructose 6-phosphate OH fructose 1,6-bisphosphate HCO; + ATP ADP + P GTP GDP + CO2 OUR OPO o . pyruvate carboxylase phosphoenolpyruvate carboxykinase CH, 0 HH oxaloacetate phosphoenolpyruvate Pyruvate

Answer 1

It is important here to understand the meaning of exergonic. Exergonic means release of energy. Association with ATP is one of the situations where a reaction can be exergonic but it necessarily is not one of the conditions for a reaction to be exergonic.

In the above mentioned reactions involving conversion of Pyruvate to Oxaloacetate or conversion of Glucose - 6 - Phosphate to Glucose, you will notice that a phosphate bond is broken (either in ATP or Glucose - 6 - Phosphate). This bond breakage results in the release of a phosphate molecule.

Hyrdolysis of phosphate bonds in both cases results in the release of energy due to which they are categorized as exergonic reactions.