Energy production (glycolysis)

The energy produced by glycolysis is dependent on whether complete oxidation is possible:

• complete aerobic glycolysis of 1 molecule of glucose to pyruvate produces:
  • ATP direct turnover:
    • 1 molecule of ATP is converted to ADP in each of hexokinase and 6-phosphofructokinase reactions
    • 4 molecules of ATP are produced from phosphoglycerate kinase and pyruvate kinase reactions
  • ATP indirect turnover:
  • 2 molecules of NADH are produced from the glyceraldehyde phosphate dehydrogenase reaction
    • these can produce:
      • 6 molecules of ATP if transported inside mitochondria via the malate-aspartate system
      • 4 molecules of ATP if transported by the glycerol-3-phosphate system
        
        
• anaerobic glycolysis of 1 molecule of glucose to lactate entails all of the above reactions but:
  • 2 molecules of NADH are oxidized to NAD+ in the lactate dehydrogenase reaction; hence, there is an indirect deficit of 6ATP
  • in muscle, where glycogen may be the original source of glucose, the hexokinase reaction is not used - 1 molecule of ATP is thus conserved

Hence, the net complete aerobic glycolysis of glucose to pyruvate can produce 6-8 molecules of ATP as opposed to 2-3 molecules of ATP for anaerobic glycolysis.

Hence, in energy terms aerobic glycolysis is preferred to anaerobic glycolysis. However, both produce relatively little energy when compared to complete oxidation of one molecule of glucose through glycolysis and the tricarboxylic acid cycle - 38 molecules of ATP.