Biochemistry: Free Energy

[marymochan]

For parts A and B of this problem, use the following standard reduction potentials, free energies, and nonequilibrium concentrations of reactants and products:

atp=3.1mM

glucose=5.1mM

nad+=350micro M

Pi=5.9mM

pyruvate=62 micro M

nadh=15micro M

adp=220 micro M

co2= 15 torr

 

half reaction

NAD⁺ + H⁺ +2e^- --> nadh E⁰ (V)=-0.315

2 pyruvate+ 6H⁺ + 4e^----> glucose E⁰=-.590

 

pyruvate + nadh + 2H⁺ ---> ethanol + nad⁺ + co2

delta G^{' naught} =-64.4kJ/mol

 

adp+ h2o --> adp + Pi + H⁺

delta G'^naught=-30.5kj/mol

 

a) consider the last 2 steps in the alcoholic fermentation of glucose by brewers' yeast:

pyruvate + nadh + 2H⁺ ---> ethanol + nad⁺ + co2

calculate the nonequilibrium concentration of ethanol in yeast cells, if delta G=-38.3 kJ/mol for this reaction at pH=7.4 and 37 degrees C when the reactants and products are at the concentrations given above.

 

the correct answer is 0.527 M but I keep getting 1.53*10^-17 molar of ethanol. what am i doing wrong?

 

b)consider the degradation of glucose to pyruvate by the glycolytic pathway:

 

glucoset+ 2adp+ 2Pi + 2nad⁺ --> 2 pyruvate + 2atp + 2h2o + 2nadh + 2H⁺

calculate delta G for this reaction at pH 7.4 and 37 degrees C.

 

the correct answer is -62.4 kJ/mol but I am not getting the same numbers.

 

TIA

Edited March 29, 2016 by marymochan