The Go, for the reaction ATP + H2O-ADP + Pi + H+ is-30.5 kJ mol. Other organopho

Question

The Go, for the reaction ATP + H2O-ADP + Pi + H+ is-30.5 kJ mol. Other organophosphate species also undergo hydrolysis of the phosphate moiety via a similar reaction. Determine the value of G°, for the following reactions and indicate if the reaction will proceed spontaneously in the direction written if the reactants and products are initially in a 1:1 molar ratio. a. ATP+ Acetic acidADPAcetyl phosphate kJ mol- The reaction is The hydrolysis reaction for acetyl phosphate is Acetyl phosphateH20Acetic acid+PH G",--42.2 kJ mol-1.) b. ATP+GlucoseGlucose-6-phosphate ADP kJ mol The reaction is (The hydrolysis reaction for glucose-6-phosphate is Glucose-6-phosphateH2OGlucose PH AG 12.5 kJ mol1)

Explanation / Answer

Ans. #a. Given,

Acetyl phosphate + H2O <------> Acetic acid + Pi + H+           ; dG0’= -42.2 kJ mol-1

# When the reaction is reversed, the numerical sign of dG0’ is also reversed.

So,

Acetic acid + Pi + H+ <------> Acetyl phosphate + H2O           ; dG0’= +42.2 kJ mol-1

# The overall coupled reaction can be written as the sum of following reaction-

   ATP + H2O <------> ADP + Pi + H+                             ; dG0’= -30.5 kJ mol-1

(+) Acetic acid + Pi + H+ <------> Acetyl phosphate + H2O     ; dG0’= +42.2 kJ mol-1

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     ATP + Acetic acid <------> ADP + Acetyl phosphate            ; dG0’net = ?

The dG0’net of the coupled reaction is given as the sum of dG0’ of the two reactions as follow-

            dG0’net= (-30.5 kJ mol-1) + 42.2 kJ mol-1 = +11.7 kJ mol-1

#b. Given,

            G-6-P + H2O <------> Glucose + Pi + H+             ; dG0’= -12.5 kJ mol-1

# When the reaction is reversed, the numerical sign of dG0’ is also reversed.

So,

            Glucose + Pi + H+ <------> G-6-P + H2O             ; dG0’= +12.5 kJ mol-1

# The overall coupled reaction can be written as the sum of following reaction-

   ATP + H2O <------> ADP + Pi + H+                             ; dG0’= -30.5 kJ mol-1

(+) Glucose + Pi + H+ <------> G-6-P + H2O                  ; dG0’= +12.5 kJ mol-1

     ---------------------------------------------------------------------------------

     ATP + Glucose <------> ADP + G-6-P                         ; dG0’net = ?

The dG0’net of the coupled reaction is given as the sum of dG0’ of the two reactions as follow-

            dG0’net= (-30.5 kJ mol-1) + 12.5 kJ mol-1 = -18.0 kJ mol-1

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