Question

Explain how reactions with positive standard Delta G's (∆G°) can still occur in cells. (biochem)

Answer 1

The basi theory of Free energy:;

In order to compare equilibirum vs. spontaneous/nonspontaneous reactions, we better use a criteria.

Recall that if dSuniverse > 0, this is spontaneous, if dSuniverse = 0, this is inequilbirium and if dSuniverse < 0 this is never possible.

Then, recall that

dSuniverse = dSsurroundings + dSsystem

dSsystem = Sproducts - Sreactants

dSsurroundings = Qsurroundings/T = -dHsystem/T

therefore

dSystem =  -dHsystem/T + dSsystem

If we multiply by -T

dGrxn = dHrxn - T*dSrxn

Now, analysis of dG value... which is the "free energy" available for a process to follow

if dG <0 , this will be spontaneous

if dG = 0 , this is in equilibrium

if dG > 0, this will not be spontaneous

Now...

We tend to forget where does dG comes from

it comes from the TOTAL ENTROPY of the universe

a biological cell can still form "reverse" reaction as long as it is increasing the total entropy of the universe

That is; how cellphones and reversible reactions work

We can form some reactions in reverse as long as we increase the entropy universe