Glycolysis

• glycolysis makes pyruvate from glucose
• • glycolysis involves splitting one molecule of glucose (6 carbons) into 2 smaller molecules of pyruvate (3C)
  • process happens in the cytoplasm of the cell
  • the first stage of both aerobic and anaerobic respiration and doesn't need oxygen to take place
• there are two stages in glycolysis:

  • phosphorylation
  • oxidation
• • first ATP is used to phosphorylate glucose to triose phosphate
  • phosphorylation is the process of adding phosphate to a molecule
  • then triose phosphate is oxidised, releasing ATP
  • overall there is a net gain of 2 ATP and 2 reduced NAD
• Phosphorylation:

  • glucose is phosphorylated using a phosphate from a molecule of ATP
  • this creates one molecule of glucose phosphate and one molecule of ADP
  • ATP is then used to add another phosphate, forming hexose bisphosphate
  • hexose bisphosphate is then split into 2 molecules of triose phosphate
• oxidation:

  • triose phosphate is oxidised (loses hydrogen) forming 2 molecules of pyruvate
  • NAD collects the hydrogen ions. forming 2 reduced NAD
  • 4ATP are produced, but 2 were used up in stage 1
  • net gain of 2 ATP
• 1 molecule of glucose gets phosphorylated

  using 1 molecule of ATP

  to produce 1 molecule of glucose phosphate
• glycolysis takes place in the cytoplasm bc glucose cant cross the the outer mitochondrial membrane

  pyruvate can cross this membrane, so the rest of the reactions in aerobic resp occur within the mitochondria
• 2 reduced NAD - to oxidative phosphorylation

  2 pyruvate - actively transported into the mitochondrial matrix for use in the link reaction

  2 ATP (net gain) - used for energy
• the products of glycolysis - anaerobic resp:

  • the pyruvate produced in glycolysis is converted into ethanol (alcohol fermentation) or lactate (lactate fermentation) using reduced NAD
• alcohol fermentation - occurs in plants and yeast:

  • pyruvate + CO2 = ethanal
  • ethanal + NAD - NADH = ethanol
• lactate fermentation: this occurs in animal cells and some bacteria:

  • pyruvate - NAD - NADH = lactate - lactic acid
• the production of lactate or ethanol regenerates oxidised NAD

  this means that glycolysis can continue even when there isn't much oxygen around

  so a small amount of ATP can still be produced to keep some biological process going
• glycolysis only produces 2 ATP, so anaerobic respiration only produces 2 ATP