c5 p4

• Formation of Acetyl Coenzyme A

  • Pyruvic acid enters the mitochondria & undergoes decarboxylation (remove CO2)
  • Pyruvate dehydrogenase converts 3C pyruvic acid to
  • 2C acetyl group plus CO22C acetyl group is attached to coenzyme A to form acetyl coenzyme A, which enter Krebs cycle
  • Coenzyme A is derived from Vitamin B
  • It behaves as a "carrier or taxi" for the 2C acetyl group

  
• Krebs Cycle


  • called the citric acid cycle, or the tricarboxylic acid (TCA) cycle
  • A series of biochemical reactions that occur in the matrix of mitochondria
  • The 2C component of acetyl CoA is pulled apart bit-by-bit to release CO2 and H+
  • The H+ are sent to the Electron Transport Chain (ETC) as NADH2 and FADH2 to be converted into energy (ATP)

  
• The Krebs Cycle

  1. Acetyl CoA (2C) enters the cycle & combines with a 4C compound to form citric acid

  2. Potential energy in the chemical bonds is released step-by-step to reduce the coenzymes (NAD+ → NADH2; FAD+ → FADH2) which temporarily store this energy

  3. NAD+ & FAD+ are H2 carriers

  
• Krebs Cycle

  • (2C) acetyl CoA + (4C) oxalo-acetic acid → (6C) citric acid
  • A series of reactions involving the elimination of 2C & 4O as 2CO2 & the removal of hydrogens occurs
  • 6C citric acid becomes 4C oxalo-acetic acid to complete the cyclic pathway

  
• The Krebs Cycle: Summary

  1. Each acetyl CoA molecule that enters the Krebs cycle produces: 2 molecules of CO2, 3 molecules of NADH2, 1 molecule of ATP, 1 molecule of FADH2

  2. Each glucose produced 2 acetyl CoA molecules

  3. Total yield = (above products) x 2

  
• Electron Transport Chain


  • Located in the mitochondria
  • Integral membrane proteins (cytochromes) form a chain which is located in the inner mitochondrial membrane
  • Each cytochrome picks up electrons and passes them on to the next in the chain
  • Small amounts of energy are released as this occurs
  • This energy is used to form ATP
  • Oxidative Phosphorylation produces the vast majority of ATP in the cell

  
• the electron transport chain

  • series of cytochromes located in the inner mitochondrial memebrne
  • hydrogens delievered to the chain are split into protons and electrons
  • as electrons are passed through the chain, there is a stepwise release of energy from the electrons for the generation of ATP
• Steps in the Electron Transport Chain

  1. Proteins of the ETC are clustered into 3 complexes that each act as proton pumps (move H+ into the inner membrane space)

  2. The electrons are shuttled from one cytochrome complex to the next

  3. Final complex passes its electrons (2H+) to a half of O2 molecule to form water (H2O)

  4. The buildup of H+ outside the inner membrane creates a positive charge, an electrochemical gradient of potential energy

  5. ATP synthase enzyme within H+ channel uses this potential energy to form ATP from ADP and iP
• Electron Transport Chain


  1. H+ ions are transported from matrix into the space between the inner & outer membranes

  2. This ensures a high concentration of H+ is established between the inner & outer membranes

  3. ATP is formed as H+ diffuses through special ATP synthase channels back to the matrix
• Summary of Aerobic Cellular Respiration

  1. Glucose (+O2) is broken down into CO2 + H2O + energy used to form ATP

  2. 2 ATPs are formed during glycolysis

  3. 2 NADH2 are formed during glycolysis

  4. 2 NADH2 are formed when converting pyruvate to acetyl CoA

  5. 2 ATPs are formed directly during Krebs Cycle

  6. 6 NADH2 are formed during Krebs Cycle

  7. 2 FADH2 are formed during Krebs Cycle

  8. For each NADH2 the proton gradient generates 3 ATP, 10 NADH2 generates 10 x 3 ATP = 30 ATP

  9. For each FADH2 the proton gradient generates 2 ATP, 2 FADH2 generates 2 x 2 ATP = 4 ATP

  10. From each glucose molecule 4 ATPs are generated

  11. Oxidative phosphorylation generates 36-38 ATPs from one glucose molecule

  
• The complete oxidation of glucose can be represented as follows: C6H12O6 + 6O2 → 36 or 38 ATP + 6CO2 + 6H2O
• Benefit


  H2 obtained from a wide variety organic molecules → funnelled → common energy carrier, ATP

  
• Involves a complex series of reactions in the mitochondrion

  
• Oxidative Phosphorylation produces the vast majority of ATP in cell
• Metabolic pathways


  Synthesise ATP
• Anaerobic


  • ATP production in absence of O2: Glycolysis
  • Small amounts of ATP
• Aerobic


  • ATP production using O2: Oxidative Phosphorylation
  • Fuel + O2 → CO2 + H2O + energy (ATP + heat)
  • Large amounts of ATP