Can anyone explain the free energy change in step 7 of glycolysis, so I can see why it is not exergonic and irreversible like steps, 1, 3 and 10? For example, in step 1:
(one of the highly exergonic--not reversible steps), the negative net free energy change is -4,000 cal/mol.
glucose + Pi --> G6P [G = +3,300 cal/mol]
ATP --> ADP + Pi [G = -7,300 cal/mol]
Therefore, in this coupled reaction, G = -4,000 cal/mol
I cannot produce the above for step 7 to show me that the reaction is not exergonic.
This is my guess, but I know I am missing something:
ADP + Pi --> ATP [G = +7,300 cal/mol]
1,3-biphosphoglycerate + H2O (hydrolysis) --> 3-phosphoglycerate [G = -11,800 cal/mol]
Therefore, in this coupled reaction, G = -4,500 cal/mol
?