In a ‘coupled reaction’ where ATP hydrolysis is used to power endergonic reactio

Question

In a ‘coupled reaction’ where ATP hydrolysis is used to power endergonic reactions (such as the production of e.g. proteins or amino acids, or similar compounds), what is the overall deltaG value of the reaction? Would it be classified as spontaneous or non-spontaneous? Make sure you describe the basic principles of coupled reactions in your answer. Use terms such as positive deltaG value, spontaneous reaction, negative deltaG value, non-spontaneous reaction, coupled reactions, energy releasing, requiring energy input.

Explanation / Answer

ATP4-+ H2O ---------> ADP3-+ Pi2- + H+

delta Go ------> -30.5 kJ/mol

The overall delta G value for the hydrolysis of one molecule of ATP . This reaction would be considered as a spontaneous reaction. A reaction is said to be spontaneous and that it would proceed on its own , when the Gibbs free energy is negative.

For reactions that have a negative Gibbs free energy are said to be spontaneous and the reaction is said to be exergonic, as it proceeds with the release of free energy. On the other hand , reactions that have a positive Gibbs free energy are said to be non spontaneous and the reaction is said to be endergonic, as it proceeds with the consumption of free energy.

The Gibbs free energy for spontaneous reactions is negative. The actual free energy change for ATP hydrolysis is not -30.5 kJ/mol, under standard conditions it is very different. The cellular concentrations of ATP are less than 1.0M standard conditions. In the cytoplasm, Mg binds to ATP and thus the relevant Gibbs free energy is for the hydrolysis of MgATP2-.

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