Question

Taking glycolysis and lactic fermentation together, the net reaction (including water!) is simple:

Glucose => 2*lactate + energy

(the energy is used for ADP+Pi => ATP+H2O)

The only changes are:

1. Molecularity: You get more molecules in the end, meaning your entropy and pressure increase.
2. Chemical links: You have C-C, C-O and O-H turned into C=O and C-H. Yet, the reaction is clearly exergonic. Why is there a significant reduction in Gibbs energy?

As far as I understood (from a professor who teaches metabolism), the change in the number of molecules is probably not the main contributor to the Gibbs energy, but rather the change in chemical links. But I don't know why.

What's more, I think (but not sure) that the formose reaction (condensation of formaldehyde to sugars) is exergonic under some conditions, though it moves in the other direction (lowering the molecularity and converting C=O and C-H to C-C, C-O and O-H).

Answer 1

The reduction in Gibbs energy in the exergonic reaction of glycolysis and lactic fermentation is primarily due to the change in chemical links. The conversion of C-C, C-O, and O-H bonds into C=O and C-H bonds releases energy.

Step-by-step explanation:

The net reaction of glycolysis and lactic fermentation is: Glucose -> 2 lactate + energy. The reduction in Gibbs energy in this exergonic reaction is primarily due to the change in chemical links rather than the change in the number of molecules.

The conversion of C-C, C-O, and O-H bonds into C=O and C-H bonds releases energy. The formose reaction, which is the condensation of formaldehyde to sugars, can also be exergonic under certain conditions even though it lowers the molecularity and converts C=O and C-H bonds to C-C, C-O, and O-H bonds.