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Orderly steps of glycolysis

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Glycolysis is a metabolic pathway that converts glucose into pyruvate, yielding ATP and NADH in the process. It takes place in the cytoplasm of the cell and is divided into two phases: the energy investment phase and the energy payoff phase. Here are the orderly steps of glycolysis:

Energy Investment Phase

  1. Hexokinase Reaction

    • Enzyme: Hexokinase (or Glucokinase in the liver)
    • Substrate: Glucose
    • Product: Glucose-6-phosphate (G6P)
    • ATP used: 1 ATP

  2. Phosphohexose Isomerase Reaction

    • Enzyme: Phosphohexose isomerase
    • Substrate: Glucose-6-phosphate
    • Product: Fructose-6-phosphate (F6P)

  3. Phosphofructokinase-1 Reaction

    • Enzyme: Phosphofructokinase-1 (PFK-1)
    • Substrate: Fructose-6-phosphate
    • Product: Fructose-1,6-bisphosphate (F1,6BP)
    • ATP used: 1 ATP

  4. Aldolase Reaction

    • Enzyme: Aldolase
    • Substrate: Fructose-1,6-bisphosphate
    • Products: Dihydroxyacetone phosphate (DHAP) and Glyceraldehyde-3-phosphate (G3P)

  5. Triose Phosphate Isomerase Reaction

    • Enzyme: Triose phosphate isomerase
    • Substrate: Dihydroxyacetone phosphate
    • Product: Glyceraldehyde-3-phosphate (G3P)
    • (At this point, there are two molecules of G3P.)

Energy Payoff Phase

  1. Glyceraldehyde-3-Phosphate Dehydrogenase Reaction

    • Enzyme: Glyceraldehyde-3-phosphate dehydrogenase
    • Substrate: Glyceraldehyde-3-phosphate
    • Product: 1,3-Bisphosphoglycerate (1,3-BPG)
    • NAD+ reduced to NADH

  2. Phosphoglycerate Kinase Reaction

    • Enzyme: Phosphoglycerate kinase
    • Substrate: 1,3-Bisphosphoglycerate
    • Product: 3-Phosphoglycerate (3PG)
    • ATP produced: 1 ATP per G3P (2 ATP total for 2 G3P)

  3. Phosphoglycerate Mutase Reaction

    • Enzyme: Phosphoglycerate mutase
    • Substrate: 3-Phosphoglycerate
    • Product: 2-Phosphoglycerate (2PG)

  4. Enolase Reaction

    • Enzyme: Enolase
    • Substrate: 2-Phosphoglycerate
    • Product: Phosphoenolpyruvate (PEP)
    • Water is released

  5. Pyruvate Kinase Reaction

    • Enzyme: Pyruvate kinase
    • Substrate: Phosphoenolpyruvate
    • Product: Pyruvate
    • ATP produced: 1 ATP per PEP (2 ATP total for 2 PEP)

Summary

In total, glycolysis converts one molecule of glucose into two molecules of pyruvate, producing a net gain of 2 ATP and 2 NADH molecules.