1. (0.75 pts) The free energy change for an enzymatic reaction under cellular co
ID: 542568 • Letter: 1
Question
1. (0.75 pts) The free energy change for an enzymatic reaction under cellular conditions must be negative for a reaction to occur in the direction as written. Thus, the concentrations of metabolites in cells need to be in favor of producing a negative @for a given enzymatic reaction. Answer the following questions for the reaction shown below. acetyl CoA + H2O CoASH + acetic acid Go,--32 kJ/mol (a) (0.2 pts) Calculate the free energy change at 25° C at pH 7.0 in a cell where the concentration of acetyl CoA, CoASH, and acetic acid are 1.2 mM, 85 M and 15 M, respectively. (Note: under standard conditions [H2O] = 1.0 M). d under the given cellular conditions or at equilibrium conditions? Why or why not?Explanation / Answer
Answer for (a):
For a reaction under standard conditions G = G0 + RTlnQ
where Q is the ratio of concentrations of the products divided by the reactants.
For the given reaction
Acetyl CoA + H2O <========> CoASH + Acetic acid…………… G0 = -32kJ/mol = - 32000 J/mol
Acetyl CoA = 1.2 mM = 0.0012 M
CoASH = 85 mM = 85 x 10-6 M
Acetic acid = 15 mM = 15 x 10-6 M
H2O = 1 M
Temperature, T = 25o C = 25 + 273 = 298 K
R = 8.3144 J K1mol1
Substituting the above values into equation G = G0 + RTlnQ one will get the following:
G = - 32000 + 8.3144 (298) ln [15 x 10-6][ 85 x 10-6] /[1.2 x 10-3]
G = - 32000 + 8.3144 (298) ln [15 x 10-6][ 85 x 10-6] /[1.2 x 10-3]
G = - 32000 + 8.3144 (298) ln [1.0624 x 10-12]
G = - 32000 + 8.3144 (298) x (-27.5705)
G = - 32000 - 68311
G = - 100311 J mol1
G = - 100.311 kJ mol1
Answer for (b):
Under equilibrium conditions Q equals to K and G becomes G0. Since G of the above reaction,is larger than G0 the reaction is more favoured under standards conditions than under equilibrium conditions.
Answer for (c):
Yes millimolar concentrations of various components of a cell, such as proteins, nucleic acids, lipids and sugars, is possible. Further concentrations of several metabolites of a cell runs into more than a millimole For example the Acetyl CoA concentration in the above reaction is given as 1.2 mM. Similarly several metabolite concentrations runts into more than a millimole or even in tens of millimolar concentrations.
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