During glycolysis ATP is synthesized from phosphoenolpyruvate (PEP) in a reactio

Question

During glycolysis ATP is synthesized from phosphoenolpyruvate (PEP) in a reaction catalyzed by the enzyme pyruvate kinase. This reaction proceeds as follows:

PEP + ADP yields ATP+ Pyruvate

A. The delta G0for the hydrolysis of PEP is -62kJ mol-1 and the delta G0 for ATP hydrolysis is -30.5kJ mol-1. Calculate the delta G0 for the pyruvate kinase reactioin from the two half reactions.

B. If the delta G for the coupled reaction is -16.7 mol-1, and there is 10 times more ATP than ADP at 250C, what is the ratio of [pyruvate]/[PEP] under these conditions?

Explanation / Answer

PEP + ADP ----------------> ATP + Pyruvate

A)   GIven that

(hydrlysis of PEP) PEP + H2O   ---------------> pyruvate + Pi      Go = - 62 kJ mol-1

(hydrlysis of ATP) ATP + H2O   ----------------> ADP + Pi           Go = -30.5 kJ mol-1

Then,

ADP + Pi ----------------> ATP + H2O    Go = + 30.5 kJ mol-1

PEP + H2O   ---------------> pyruvate + Pi      Go = - 62 kJ mol-1

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

PEP + ADP ----------------> ATP + Pyruvate     

Gorxn = + 30.5 kJ mol-1 - 62 kJ mol-1 = - 31.5 kJ mol-1

Therefore,

Gorxn = - 31.5 kJ mol-1

B) Given that

PEP + ADP ----------------> ATP + Pyruvate Grxn = - 16.7 kJ mol-1

Futher given that 10 times more ATP than ADP i.e. [ATP]/ADP]= 10

We know that

G =  Go + RT In Keq

- 16.7 kJ mol-1 = - 31.5 kJ mol-1 + RT In { [ATP] [Pyruvate]/[PEP] [ADP]}

- 16.7 kJ mol-1 = - 31.5 kJ mol-1 + (8.314 J/K/mol) (298 K) In { [ATP] [Pyruvate]/[PEP] [ADP]}

14.8 kJ mol-1 = (8.314 J/K/mol) (298 K) In { [ATP] [Pyruvate]/[PEP] [ADP]}

14800 J mol-1 = (8.314 J/K/mol) (298 K) In { [ATP] [Pyruvate]/[PEP] [ADP]}

{ [ATP] [Pyruvate]/[PEP] [ADP]} = 393

{[Pyruvate]/[PEP]} {[ATP]/ADP]} = 393

{[Pyruvate]/[PEP]} x 10 = 393                       { since, [ATP]/ADP] = 10 }

[Pyruvate]/[PEP] = 39.3

Therefore,

ratio of [pyruvate]/[PEP] = 39.3

Related Questions

Navigate

• Browse (All)
• Browse D
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.