The TCA cycle operates under aerobic conditions despite O2 not directly participating, as ATP and NADPH produced are utilized in the electron transport chain where O2 is essential. The complete oxidative degradation of phosphoenolpyruvate (PEP) to CO2 and H2O generates a net of 1 ATP due to the activity of the glycerol phosphate shuttle. During glycolysis, the conversion of PEP to pyruvate produces 2 ATP, but one is offset by the reduction of 1 ATP when dihydroxyacetone phosphate is converted to glycerol-3-phosphate.

1. Although O_2 does not participate directly in the reactions of the TCA cycle, the cycle operates
only under aerobic conditions. Briefly explain this fact. How many ATP molecules are
generated during the complete oxidative degradation of phosphoenolpyruvate (PEP) to CO_2
and H_2O? Assume the glycerol phosphate shuttle is operating and show how you arrived at
your answer.
Solution
2) even though oxygen does not participate in the TCA Cycle but the ATP and NADPH
produced are passed in the ETC cycle where the oxygen acts as a electron transport.. Hence there
the role of oxygen takes place which is not found in the case of anaerobic situations..
3) when PEP gets converted to pyurvate I release 2 molecules of ATP.. But in this case only 1
ATP is produced as the one molecule of di-hydrooxyacetone phosphate converted to glyecerol-3-
phosphate by glycerol cycle hence in the glycolysis step 1 molecule gets reduced hence 1 ATP
gets reduced..!!