Topic 2: Glycolysis

Glycolysis

  • Breaks down glucose to form 2 3-carbon molecules (pyruvate)
  • ATP is formed by substrate-level phosphorylation
  • Occurs in the cytoplasm
  • Will occur whether or not O2

  is present

Glycolysis is like a game of tag that happens inside our cells. The players are called enzymes and they pass a ball (glucose) around. Each time they pass the ball, they tag it with a special chemical (ATP). When the ball gets tagged enough times, it splits into two smaller balls (pyruvate) and the game is over. The players get to keep the tags they collected and use them to play other games.

Energy Production

  • Transfers only 2.2% of the free energy available in glucose to ATP
  • The majority of the energy is still trapped in NADH and pyruvate molecules

Steps of Glycolysis

  • Step 1:
    • Transfer of a phosphate group from ATP to carbon 6 of glucose forming glucose 6-phosphate facilitated by hexokinase
    • Kinase is an enzyme that adds phosphate groups
  • Step 2:
    • Glucose 6-Phosphate to Fructose 6-phosphate is an isomerization reaction facilitated by phosphoglucose isomerase
    • Isomerase is an enzyme that causes structural change
  • Step 3:
    • Transfer of P-group from ATP to the carbon 1 of Fructose 6-phosphate to become Fructose 1,6-bisphosphate
  • Step 4:
    • Fructose 1,6-bisphosphate splits into 2 3-carbon molecules that are isomers of each other:
    • Dihydroxyacetone phosphate (DHAP)
    • Glyceraldehyde 3-Phosphate (G3P)
      • Aka phosphoglyceraldehyde (PGAL)
  • Step 5:
    • DHAP is converted into another molecule of (G3P)
  • Step 6:
    • A phosphate group from the cytoplasm attaches to G3P
    • NAD+ gains 2 electrons to form NADH + H+
    • 1,3-Bisphosphoglycerate is formed
  • Step 7:
    • Previous step forms a high-energy bond to the phosphate that was added
    • This phosphate is transferred to ADP to make ATP
    • 3-phosphoglycerate is left
  • Step 8:
    • Isomerization occurs to 3-phosphoglycerate (phosphate moves to second carbon) to form 2-Phosphoglycerate
  • Step 9:
    • A molecule of water is removed
    • Phosphoenolpyruvate (PEP) is formed
  • Step 10:
    • A phosphate group is transferred from PEP to ADP to make and ATP
    • You are left with a pyruvate

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