Glycolysis (DP IB Biology)

Glycolysis

• Glycolysis is the first stage of respiration

• It takes place in the cytoplasm of the cell and involves:

  • Trapping glucose in the cell by phosphorylating the molecule

  • Splitting the glucose molecule in two

• It results in the production of

  • Two pyruvate (3 carbon/3C) molecules

  • Net gain two ATP (Four ATP are produced in total but two are used during the reactions of glycolysis)

  • Two reduced NAD

Steps of glycolysis

• Phosphorylation: glucose (6C) is activated by phosphorylation from two ATP to form fructose-1,6-bisphosphate (6C)

  • This makes the 6C molecule less stable and therefore more reactive

Glucose + 2ATP → Fructose-1,6-bisphosphate

• Lysis

  • Fructose-1,6-bisphosphate (6C) splits into two molecules of triose phosphate (3C)

Fructose-1,6-bisphosphate → 2 Triose phosphate

• Oxidation:

  • Hydrogen is removed from each molecule of triose phosphate by dehydrogenase enzyme and transferred to coenzyme NAD to form two reduced NAD

  • Triose phosphate is oxidised to for another 3C molecule glycerate-3-phosphate

2 Triose phosphate →2 Glycerate-3-phosphate
4H + 2NAD → 2NADH + 2H⁺

• ATP formation

  • Phosphates are transferred from the intermediate substrate molecules to form four ATP through substrate-linked phosphorylation

4P_i + 4ADP → 4ATP

• Two molecules of pyruvate are produced as the end product of glycolysis which can be used in the next stage of respiration

• Each step in the pathway is catalysed by a different enzyme

Glycolysis, the formation of two pyruvate molecules from one glucose sugar molecule