Glycolysis (Edexcel International A Level Biology): Revision Note

Glycolysis

• Glycolysis is the first stage of respiration

• It does not require oxygen to take place and is therefore the first step for both aerobic and anaerobic respiration

• Glucose is only partially oxidised during glycolysis

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

  • Trapping glucose in the cell by phosphorylating the molecule

  • Oxidising triose phosphate (by losing hydrogen)

• It results in the production of

  • 2 Pyruvate (3C) molecules which moves into the matrix of mitochondria to be used during the link reaction

  • Net gain 2 ATP

  • 2 reduced NAD, which will be used during a later stage called oxidative phosphorylation

• Under anaerobic conditions, glycolysis produces lactic acid or lactate instead of pyruvate

Steps of glycolysis

• Phosphorylation of glucose (a hexose sugar)

  • Two molecules of ATP are required to provide the two phosphates needed for the phosphorylation of glucose

  • This produces

    • Two molecules of triose phosphate 

    • Two molecules of ADP

• Oxidation of triose phosphate

  • After triose phosphate loses hydrogen, it forms two molecules of pyruvate

  • The hydrogen ions are collected by NAD which reduces the coenzyme

  • This forms two reduced NAD or NADH

  • Even though a total of four ATP molecules were produced during glycolysis, two of them were used to phosphorylate glucose

  • There was therefore a net gain of two ATP molecules

The process of glycolysis