Energetics questions that you should be familiar with from the thermodynamics le
ID: 580620 • Letter: E
Question
Energetics questions that you should be familiar with from the thermodynamics lecture: Example The Go for the hydrolysis of PEP (Phosphoenol pyruvate)--62.2 kJ/mol The Go for the hydrolysis of ATP =-30.5 kJ/mol (a) What is the AG° value for the pyruvate kinase reaction: ADP + PEP ATP + pyruvate (b)What is the equilibrium constant for this reaction? (c) If the intracellular concentrations of [ATP] and [ADP] are fixed at 8 mM and 1 mM respectively, what will be ratio of pyruvate/[PEP] when the pyruvate kinase reaction reaches equilibrium?Explanation / Answer
a) dGo reaction = dGo ( ATP hydrolysis) - dGo ( PEP hydrolysis)
= -30.5 KJ/mol - (-62.5 KJ/mol) = 32 KJ/mol = 32000 J/mol
b) we have relation dGo = RT ln Keq
32000 J/mol = - 8.314 J/molK x 298 K x ( ln Keq)
ln Keq = 12.916
Keq = exp ( - 12.916) = 2.46 x10^-6
c) Keq = [ATP] [Pyruvate] / [ADP] [PEP]
2.46 x 10^-6 = (8mM) [Pyruvate] / ( 1mm) ( [PEP]
[Pyruvate] /[PEP] = 3.07 x 10^-7
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