# How do cellular conditions change the Gibbs free energy of a reaction?

How do cellular conditions change the Gibbs free energy of a reaction? Taking glycolysis as an example, how exactly would cellular conditions affect the free energy released from this reaction?

• en.wikipedia.org/wiki/Glycolysis#Free_energy_changes Jan 19, 2021 at 17:23
• Standard free energy or actual free energy? Jan 19, 2021 at 22:08
• And this wouldn't be a homework question by any chance? In any case, what attempt have you made to answer it yourself? Jan 19, 2021 at 22:11

To understand that, you must have a basic understanding of Gibbs-Helmholtz equation. it states-

$$\Delta G'=\Delta G^{'o} +RT\,ln\,(Q)$$

Here, $$\Delta G'$$ = biochemical free energy change & $$\Delta G^{'o}$$ = standard biochemical free energy change.

Suppose you have a reaction, $$x+FADH_2\rightleftharpoons xH_2+FAD$$

So, $$Q=\dfrac{[xH_2][FAD]}{[x][FADH_2]}$$

Now let's assume that $$\Delta G^{'o}>0$$.

Hence the spontaneity of the aforesaid reaction (in forward direction) will be dependent on the $$\Delta G^{'o}$$, which is a function of reaction quotient (Q) as well as temperature (T).

Now, if the body is in lower energy state, i.e. fasting; $$\dfrac{[FAD]}{[FADH_2]}$$ ratio will be high. So, in order to make $$\Delta G'<0$$, the following condition must be satisfied $$-$$

$$RT\,ln\,(Q)+\Delta G^{'o}<0$$,

or, $$RT\,ln\,(Q)< -\Delta G^{'o}$$

or, $$RT\,ln \dfrac{[xH_2][FAD]}{[x][FADH_2]}\,< -\Delta G^{'o}$$

With this reasoning, be it any metabolic pathway; we can predict its spontaneity.

• 1. I don't see how this answers the poster's question. You are just explaining how the free energy change allows one to predict the direction of one particular reaction from the concentration of reactants. 2. Strictly speaking the prime indicates "at pH7". So one answer to the question might be that if the cellular pH changes this will alter the free energy change. However, the poster has not responded to either of my pertinent questions, so it is not clear what he is about. Jan 20, 2021 at 11:32
• I guess the poster has asked about free energy change in different cellular environment. So I briefly mentioned about different factors. Jan 20, 2021 at 12:21