Edexcel A (SNAB) A Level Biology:复习笔记7.2.3 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