Question

Glycerol 3-phosphate dehydrogenase catalyzes the reversible reaction:
G3P + NAD+ --> NADH + H+ + DHAP
If in the cell, the concentrations of G3P, NAD+, NADH, and DHAP are 2 mM, 4 mM, 6 mM, and 8 mM respectively. Determine if the reaction spontaneous as written?

DHAP + 2e– + 2H+ -->G3P DE'° = –0.29 V
NAD+ + H+ + 2e– --> NADH DE'° = –0.32 V

Answer 1

Heya @jthec
Do you know how to relate standard reduction potentials to free energy changes?

Answer 2

If not I just go over the theory and help you solve the problem from the start.

Answer 3

I found the overall standard reduction potential difference (-0.03V) and then plugged that into the equation DG = -nFDE

Answer 4

But then what do I do with the concentrations? Do I need them?

Answer 5

You sure do! :) And now I shall show you why (be patient with me, it takes a little time to write out the math)

Answer 6

Do I then use the value I got for DG', to plug into the equation DG = DG' + RTln[products]/[reactants]

Answer 7

Yes. that is it yes.

Answer 8

Awesome, thanks

Answer 9

Cause the when you calculate the \(\textbf{standard}\) reduction potential difference under the biochemical exception condition you assume:
1) all concentrations to be 1 M
2) the pH to be 7

So by calculating that first you got the standard free energy, but then by adding a correction term you can account for the concentrations as you just said! :)

Answer 10

Thank-you so much

Answer 11

No problem, you really solved it your self, so well done!