Question

Sucrose phosphorylase catalyzes the phosphoralytic cleaveges of sucrose in certain microorganisims

Sucrose + P----> glucose-1-phosphate + fructose

Given these reactions are:

Sucrose + H2O --> glucose + fructose (DeltaG°’ = -29.3 kJ/mol)

Glucose-1-phosphate + H2O ----> glucose + Pi (DeltaG°’ = -20.9 kJ/mol)

Calculate the Delta G°’ = -1.7 kJ/mol for the reaction

Calculate the Keq for reaction at 25C (assuming the deltaG=0)

Answer 1

we have

1) Sucrose + H2O --> glucose + fructose G°’ = -29.3 kJ/mol

2) Glucose-1-phosphate + H2O ----> glucose + Pi   G°’ = -20.9 kJ/mol

for  the phosphoralytic cleaveges of sucrose we have

3) Sucrose + P----> glucose-1-phosphate + fructose

this reaction is resulted by

Sucrose + H2O --> glucose + fructose

+ glucose + Pi  ----> Glucose-1-phosphate + H2O

therefore   G°’ for the reaction 3 is

    G°’ = (-29.3 kJ/mol)- (-20.9 kJ/mol)

= -8.2 kj/mol

G°’ for this reaction is -8.2 kj/mol.

the keq for this reaction can be calculated as

G° = -RT lnKeq

-8.2 kj/mol = - 8.314 j/kmol x 298 k x lnkeq

lnkeq= 3.309

keq = 27.4

the Keq for reaction at 25C is 27.4.