Question

How is ATP hydrolysis reaction a coupling process?

Answer 1

By itself, `"ATP"` hydrolysis is not a coupling process.

Explanation:

The hydrolysis of `"ATP"` is highly exergonic.

`"ATP " + "H"_2"O" → "ADP" + "P"_i`; `ΔG = "-30.5 kJ/mol"`

The process is highly favourable, so it happens spontaneously.

Many enzymes can use the free energy released by the hydrolysis of `"ATP"` to drive a thermodynamically unfavourable reaction.

This process is `"ATP"` coupling.

For example, the conversion of glucose to glucose-6-phosphate is thermodynamically unfavourable.

`"glucose " + "P"_i → "glucose-6-P" + "H"_2"O"`; `ΔG = "+14.3 kJ/mol"`

The enzyme hexokinase brings these two reactions together, so that the energy released by the hydrolysis of `"ATP"` can drive the synthesis of glucose-6-phosphate.

The reactions are

`"glucose " + cancel("P"_i) → "glucose-6-P" + cancel("H"_2"O")`; `ΔG = "+14.3 kJ/mol"`

`"ATP " + cancel("H"_2"O") → "ADP" + cancel("P"_i)`; `ΔG = "-30.5 kJ/mol"`

`bar("glucose " + "ATP" stackrel("hexokinase")(→) "glucose-6-P" + "ADP")`; `ΔG = "-16.2 kJ/mol"`

The coupled reaction has a negative free energy, so the process is thermodynamically favourable.