Glycolytic pathway

• Glycolysis

  The sequence of reactions that converts glucose into pyruvate with the production of ATP
• Glycolysis

  • It is the prelude to the citric acid cycle and the electron transport chain in aerobic organisms, where most of the energy contained in glucose is released
  • Under aerobic conditions, pyruvate enters the mitochondria where it is completely oxidized to CO2 and H2O
  • If the supply of oxygen is insufficient, e.g. in actively contracting muscle, pyruvate is converted into lactate
  • In some anaerobic organisms, pyruvate is transformed into ethanol
• Embden Meyerhof pathway

  Another name for glycolysis, after Gustav Embden and Otto Meyerhof who made significant contributions to its elucidation in 1940
• Types of reactions found in the glycolytic pathway

  • Phosphoryl Transfer
  • Isomerization
  • Dehydration
  • Aldol Cleavage
• The glycolytic pathway

  1. Conversion of Glucose to fructose 1,6-Biphosphate (Priming stage, 3 steps)

  2. Splitting stage (4 steps)

  3. Last stage leading to generation of pyruvate (3 steps)
• Phosphorylation (step 1)

  Glucose + ATP -> Glucose 6-phosphate + ADP + H+
• Glucose 6-phosphate

  • Glucose inside cells has only 1 fate: it is phosphorylated to form Glucose 6-Phosphate
• Fates of Glucose 6-phosphate

  1. Isomerization, catalyzed by Phosphoglucose Isomerase (Glucose 6-phosphate -> Fructose 6-phosphate)

  2. Another phosphorylation, catalyzed by Phosphofructokinase (Fructose 6-phosphate + ATP -> Fructose 1,6-bisphosphate + ADP + H+)
• Phosphofructokinase (PFK)

  An allosteric enzyme whose catalytic activity is critically dependent on and controlled by ATP and other metabolites
• Splitting stage of glycolysis

  1. Fructose 1,6-bisphosphate -> Dihydroxyacetone phosphate + Glyceraldehyde 3-phosphate (catalyzed by Aldolase)

  2. Conversion of Dihydroxyacetone phosphate to Glyceraldehyde 3-phosphate (catalyzed by Triose phosphate isomerase)
• Conversion of glyceraldehyde 3-phosphate to 1,3-biphosphoglycerate

  Gly 3-P + NAD+ + Pi -> 1,3-DPG + NADH + H+ (catalyzed by Glyceraldehyde 3-phosphate dehydrogenase)
• Conversion of 1,3-biphosphoglycerate to 3-phosphoglycerate

  1,3 Diphosphoglycerate + ADP -> 3-Phosphoglycerate + ATP (catalyzed by Phosphoglycerate Kinase)
• Last stage of glycolysis leading to pyruvate


  1. 3-phosphoglycerate -> 2-phosphoglycerate (catalyzed by Phosphoglyceromutase)

  2. 2-Phosphoglycerate -> Phosphoenol pyruvate + H2O (catalyzed by Enolase)

  3. PEP + ADP + H+ -> Pyruvate + ATP (catalyzed by Pyruvate Kinase)
• The net reaction in the conversion of Glucose into pyruvate
• Consumption and Generation of ATP in Glycolysis

  Glucose -> Glucose 6-Phosphate: -1 ATP

  Fructose6-phosphate -> Fructose 1,6-bisphosphate: -1 ATP

  2 1,3-Biphosphoglycerate -> 2 3-phosphoglycerate: +2 ATP

  2 PEP -> 2 Pyruvate: +2 ATP

  NET: +2 ATP