Glycolysis, glycerol phosphate shuttle

[aleaiactaest]

I'm a little confused about one step regarding glycolysis and the glycerol phosphate shuttle, I'm going to walk you through my thoughts..

 

* During glycolysis we get 2 NADH for every glucose molecule

* NADH needs a shuttle system to pass the inner membrane of the mitochondria

* The first step of the glycerol phosphate shuttle is when the GPDH-C enzyme catalyzes the following redox reaction:

DHAP + NADH -> 3PG + NAD+

* As I see it we are getting down on lower energy state regarding both 3PG and NAD+. NAD+ is obviously at a lower energy sate as NADH is carrying energy in form of electrons. Looking at the glycolysis process we gain 1 NADH and 1 ATP by going from DHAP to 3PG so it looks to me as 3PG should therefore be at a lower energy state than DHAP.

* Now as we continue in the shuttle system with GPDH-M we go from 3PG back to DHAP (lower energy to higher) and at the same time FAD+ -> FADH2 (lower energy to higher)

* It would make sense to me that 3PG was in fact at a higher energy state than DHAP, but looking at the glycolysis process i just can't see how.

 

I hope my explanations are decent enough

[BabcockHall]

3PG is not the same thing as glycerol phosphate. Draw out the structures and assign oxidation numbers to carbon, and the difference becomes obvious.