Anaerobic respiration

• Glycolysis


  1. Investing phosphorylation of glucose by 2 ATP

  2. Cleaving Fructose 1-6 bisphosphate

  3. Harvesting 4 molecules of ATP

  4. Glucose is cleaved into 2 x 3C molecules: dihydroxyacetone phosphate (DHAP) and glyceraldehyde-3-phosphate (GALP)

  5. GALP is dehydrogenated (oxidised) and phosphorylated to 1,3-biphoshoglycerate

  6. 1,3-biphoshoglycerate is hydrolysed to 3-phosphoglycerate

  7. 3-phosphoglycerate is dehydrated to phosphoenolpyruvate

  8. Phosphoenolpyruvate is hydrolysed to form pyruvate
• Hexokinase

  Irreversible phosphorylation of glucose to make glucose-6-phosphate, making it more reactive and keeping it inside the cell
• Phosphofructokinase

  Second phosphorylation, forming fructose-1,6-bisphosphate, this enzyme regulates the pace of glycolysis
• Aldolase

  Cleaving fructose 1,6-bisphosphate into dihydroxyacetone phosphate (DHAP) and glyceraldehyde-3-phosphate (GALP)
• Triose phosphate isomerase

  DHAP and GALP are isomers of each other and can readily inter-convert
• Glyceraldehyde 3-phosphate dehydrogenase

  GALP is dehydrogenated (oxidised), NAD is reduced to NADH and H+, this oxidisation is coupled to the phosphorylation of the C1 carbon, producing 1,3-biphosphoglycerate
• Phosphoglycerate kinase

  1,3-biphosphoglycerate has a high energy bond that is hydrolysed to release ATP, producing 3-phosphoglycerate
• Anaerobic respiration in animals

  Glucose -> 2 ATP (glycolysis) -> 2 Pyruvate -> (fermentation)-> 2 Lactate
• Lactate dehydrogenase (LDH)

  Catalyses the reversible reaction to produce lactate, regenerating NAD+
• Fate of lactate

  Taken up by the liver where it is re-oxidised to pyruvate and enters aerobic respiration
• Anaerobic respiration in plants and yeast

  Fermentation produces CO2 and ethanol
• Methanogenesis

  
  

  • occurs in the guts of ruminants
  • Carbohydrates (including cellulose) are hydrolysed to glucose by bacteria and archaea, which is then converted to volatile fatty acids (VFAs) like acetic, propionic and butyric acids
  • VFAs are absorbed and used as respiratory substrates
  • Methanogenic bacteria use the H2 and CO2 produced to perform anaerobic respiration, producing methane as the terminal electron acceptor
• Anaerobic respiration in sulphur bacteria

  Sulphate is used as the terminal electron acceptor, being reduced to sulphite and then sulphide
• Fast twitch muscle fibres

  • Used for sudden, powerful movements
  • rely mainly on anaerobic alactic respiration using creatine phosphate to regenerate ATP without the build-up of lactic acid
  • can convert pyruvate into gylcogen
• How can glycolysis help animals with Environmental extremes (e.g. cold)

  • starts with glycolysis but pyruvate doesn't form lactic acid
  • instead pyruvate is transaminating to alanine and proline which prevent freezing by lowering the super-cooling point
• Steps of glycolysis

  • Investing
  • Cleaving
  • Harvesting
• Glycolysis - Investing

  Investing

  • phosphorylation of glucose to make it more reactive to keep it inside its cell by 2 x ATP.
  • First phosphorylation:
  • glucose -> Glucose-6-phosphate via enzyme hexokinase (irreversible)
  • glucose-6-phosphate -> Pyruvate, producing byproducts glycogen and ribose
  • isomerisation of glucose-6-phosphate, glucose -> fructose, preventing further transformations
  • Second phosphorylation:
  • phosphorylation of the hydroxyl group (OH) on the Carbon 1 forming fructose-1,6-bisphosphate via enzyme phosphofructokinase which regulates the pace of glycolysis
• Glycolysis - Cleaving

  • fructose-1,6-bisphosphate is split into 2x 3C molecules:
  • dihydroxyacetone phosphate (DHAP)
  • glyceraldehyde-3-phosphate (GALP) via enzyme aldolase
  • DHAP and GALP are isomers of each other and can readily inter-convert via enzyme triose-phosphate isomerase
  • GALP is used in the next step of glycolysis, eventually, all the DHAP is depleted (converted into GALP)
  • 2 x GALP is formed from each molecule of glucose
• Glycolysis - Cleaving

  • 2 molecules of GALP with 1 phosphate each make 4 x ATP
  • phosphorylation:
  • GALP is dehydrogenated (loss of hydrogen)/ oxidised by enzyme glyceraldehyde 3-phosphate dehydrogenase
  • NAD+ is reduced to NADH and H+ (NAD+ -> NADH + H+)
  • oxidisation is coupled to the phosphorylation of the carbon 1, product = 1,3-biphosphoglycerate