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Gluconeogenesis:- Gluconeogenesis Is Energetically Expensive, but Essential

المؤلف:  David L. Nelson، Michael M. Cox

المصدر:  Lehninger Principles of Biochemistry

الجزء والصفحة:  548

2026-06-02

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Gluconeogenesis:- Gluconeogenesis Is Energetically Expensive, but Essential

The sum of the biosynthetic reactions leading from pyruvate to free blood glucose (Table 14–3) is 2Pyruvate+4ATP+2GTP+2NADH+2H+4H₂O→glucose+4ADP+2GDP+6Pi+2NAD⁺ (14–9)

For each molecule of glucose formed from pyruvate, six high-energy phosphate groups are required, four from ATP and two from GTP. In addition, two molecules of NADH are required for the reduction of two molecules of 1,3-bisphosphoglycerate. Clearly, Equation 14–9 is not simply the reverse of the equation for conversion of glucose to pyruvate by glycolysis, which requires only two molecules of ATP: Glucose+ 2ADP + 2Pi +2NAD⁺→ 2pyruvate 2ATP+ 2NADH+ 2H + 2H₂O

The synthesis of glucose from pyruvate is a relatively expensive process. Much of this high energy cost is necessary to ensure the irreversibility of gluconeogenesis. Under intracellular conditions, the overall free-energy change of glycolysis is at least -63 kJ/mol. Under the same conditions the overall ΔG of gluconeogenesis is -16 kJ/mol. Thus, both glycolysis and gluconeogenesis are essentially irreversible processes in cells.