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Glycolysis (Figure 1) is a process to breakdown of glucose to simpler molecules by releasing energy in every cell. Intermediate products formed for other metabolic pathways. Glycolysis occur inside cytoplasm.

Pyruvate is the end product in glycolysis. Under aerobic condition, pyruvate is oxidized to form acety-CoA which enter Krebs cycle in mitochondria. Adequate oxygen is required to oxidize the NADH and FADH2 formed. Thus, it is called aerobic glycolysis. Meanwhile, pyruvate is converted to lactate under anaerobic condition.


Figure 1: Glycolysis

Reactions in Glycolysis

Glycolysis convert glucose to pyruvate in 10 reaction steps:

  1. Phosphorylation of glucose to glucose-6-phosphate by enzyme hexokinase or glucokinase with utilization of one mole of ATP.
  2. Isomerization of glucose-6-phospate to fructose-6-phosphate by glucosephosphate isomerase.
  3. Phosphorylation of fructose-6-phosphate to fructose-1,6-bisphosphate by phosphofructokinase with utilization of one more of ATP.
  4. Cleavage of fructose-1,6-bisphosphate to 3-carbon fragments, glyceraldehyde-3-phosphate and dihydroxyacetone phosphate by aldolase.
  5. Isomerization of dihydroxyacetone phosphate to glyceraldehyde-3-phosphate by triose phosphate isomerase.
  6. Oxidation of glyceraldehyde-3-phosphate by glyceraldehyde-3-phosphate dehydrogenase.
  7. Transfer of phosphate group from 1,3-bisphosphoglycerate to form 3-phosphoglycerate by phosphoglycerate kinase with production of one mole of ATP
  8. Isomerization of 3-phosphoglycerate to 2-phosphoglycerate by phosphoglycerate mutase.
  9. Dehydration by enolase.
  10. Transfer of phosphate group from phosphoenolpyruvate to form pyruvate with production of one mole of ATP.



  1. Champe, PC, Harvey, RA. 2007. Biochemistry. Lippincott’s Illustrated Review. 4th Edition. Lippincott Williams & Wilkins.
  2. Murray, RK, Bender, DA, Botham, KM, Kennelly, PJ, Rodwell, VW, Weil, PA. 2006. Harper’s Illustrated Biochemistry, 28e. Lange, McGraw Hill.