The G°’ value for the malate DH reaction is +7.10 kcal/mol, and the G°’ value fo

Question

The G°’ value for the malate DH reaction is +7.10 kcal/mol, and the G°’ value for the citrate synthase reaction is -7.53 kcal/mol. Determine Keq for the combined, coupled reaction (e.g., L-malate <--> citrate, plus ancillary cofactors, reactants, and side-products), and compare this value to Keq for the malate DH reaction alone. By what factor do you have to multiply the Keq of the malate DH reaction to equal the Keqfor the coupled reaction. Assume a temperature of 37 °C and report your answer to the nearest ones.

Explanation / Answer

When we had coupled reactin ,   then dG of coupled reaction = - 7.53 + 7.1 = - 0.43 KCal/mol

               = ( -0.43) x ( 4.184) KJ/mol = - 1.79912 KJ/mol = - 1799.12 J/mol

Now dG = -RT ln Keq      , T = 37C = 37+273 = 310 K

for coupled reaction    -1799.12 = -8.314 x 310 ln Keq

Keq for coupled reaction = 2

Now for malate reaction dG = 7.1 KCl/mol = 7.1 x4.184 KJ/mol = 29.7064 KJ/mol = 29706.4 J/mol

Now dG = -RT ln Keq

29706.4 = -8.314 x 310 ln Keq

Keq for Malate reaction = 1 x 10^ -5

Now Keq coupled/ Keq malate = 2 / ( 10^-5) = 2 x 10^5 = 200, 000 i.e 2 lakh .

Therefor by factor of 2 lakh we need to multiply Keq of malate to equal to coupled reaction

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