Energy and Metabolism

ID #2202

If glycolysis doesn't require oxygen, then how come oxygen is a reactant in the equation? Glucose + 6O2 -> 6CO2 + 6H2O


The reaction you're discussing is the overall reaction for aerobic cellular respiration, not just glycolysis. A good way to remember that is if you think about how you do respiration, you breathe in oxygen and breathe out CO2, so it's like that process on a cellular level. 

In aerobic cellular respiration (which includes glycolysis, pyruvate oxidation, Kreb's cycle, ETC, and oxidative phosphorylation via the ATP synthase) glucose is broken down into its carbons (in the most stable form of CO2) and it's hydrogens (in the most stable form of water), releasing energy. To form the water at the end of the ETC, you need the final electron acceptor (oxygen). Without oxygen, the ETC doesn't work because there is no final electron acceptor and Kreb's cycle gets backed up. Only glycolysis can work without oxygen AND only if you recycle your cofactor through fermentation to keep glycolysis going. 

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