Aerobic Respiration

• Glycolysis


  The process of partially oxidizing glucose into pyruvate

  
• Transition (Pyruvate to Acetyl-CoA)

  The process of oxidizing pyruvate into acetyl-CoA and transporting it into the mitochondria

  
• CAC


  The citric acid cycle, the process of completely oxidizing acetyl-CoA
• Oxidative phosphorylation


  The process of producing ATP using the energy from the electron transport chain

  
• Anaerobic respiration


  The process of producing ATP without oxygen, using an alternative electron acceptor
• Lactic acid fermentation


  The process of producing ATP without oxygen, converting pyruvate to lactic acid
• Alcohol fermentation


  The process of producing ATP without oxygen, converting pyruvate to ethanol and carbon dioxide
• Glycolysis & CAC – The Complete Oxidation of Glucose


  1. Digestion: Enzymes break down large polymers into monomers

  2. Monomers enter cells for oxidation

  3. Glycolysis: Glucose is partially oxidized into Pyruvate

  4. Transition from cytosol to mitochondria: Pyruvate is oxidized into Acetyl CoA

  5. CAC: Complete oxidation of Acetyl CoA

  
• Glycolysis


  • 10 small steps, each one catalysed by a specific enzyme
  • Glucose is now trapped
  • Main regulatory step
  • High energy e- carriers
  • Substrate-level phosphorylation to make ATP

  
• Substrate-level phosphorylation


  ATP is made by direct transfer of a phosphate group from an organic substrate to ADP, catalysed by an enzyme

  
• Reduction of NAD+ into NADH

  The energy of the electrons is now carried by the reduced NADH "electron carrier"
• Glycolysis is taking place in the cytosol
• One 6-Carbon Glucose is oxidised into two 3-Carbon Pyruvate

  
• Enzymes couple oxidation reactions to energy storage (Dehydrogenase)

  
• NAD+ electron carriers are reduced into high energy NADH
• A little ATP is formed by substrate-level phosphorylation
• Glycolysis is performed in many cells (both aerobic and anaerobic organisms)
• Glycolysis is a very ancient mechanism, likely evolved before photosynthesis – does not require O2

  
• Stores of NAD+ are finite
• If O2 is not present, NADH accumulate, and the cell run out of NAD+
• Two possible pathways allow the cell to continue producing ATP without the use of oxygen: Fermentation and Anaerobic respiration
• If oxygen is present, then we can have cellular respiration
• Oxidative Phosphorylation


  Electron transport chain & chemiosmosis

  
• Electron transport chain


  • Electrons are donated by the carriers (NADH and FADH2)
  • Electrons "fall" towards ever-more electronegative partners within the inner membrane of the mitochondria, becoming less and less energetic
  • The energy they release can be harvested to pump H+ and eventually to make ATP
  • The final electron acceptor (the most electronegative of all!) is Oxygen

  
• Oxidative phosphorylation


  Electron transport chain + chemiosmosis

  
• Electron transport chain - key ideas

  • Electrons are donated by NADH and FADH2
  • Redox partners in the chain are organised in order of increasing electronegativity
  • NADH offload its electrons at Complex I, FADH2 at Complex II. NAD+ and FAD are replenished
  • Electrons "flow" from Complex I to IV
  • Ubiquinone (Q) and cytochrome c (Cyt c) move within the fluid inner membrane to pass on electrons btw Complexes
  • The energy lost by electrons along the chain is harvested by Complexes I, III and IV to pump H+ from the matrix into the intermembrane space
  • An electrochemical gradient of H+ (ie, difference in charge and concentration) is created across the inner membrane
  • The electrons finish their journey by reducing O2 (the final acceptor) into H2O
  • H+ can flow through the ATP synthase, down their concentration gradient, powering the rotor, and allowing the phosphorylation of ADP + Pi into ATP

  
• ATP synthase


  • A most amazing molecular machine
• [H+] (intermembrane space)


  [H+] (Matrix)
• Proton gradient ("proton-motive force")


  • Can be used for flagellar rotation in bacteria
  • Can be used for import/export through the inner membrane
• 1 NADH <-> ~2.5 ATP
• 1FADH2 <-> ~1.5 ATP
• 1 Glucose <-> about 30 ATP
• About 34% of the energy contained in Glucose is harvested in the form of ATP
• The rest dissipate as heat
• Where do these "about" come from??
• Oxygen acts as an acceptor of electrons during this process.
• Electrons are passed from one carrier to another along the electron transport chain, releasing energy at each step.
• Electron transport chain - series of protein complexes embedded within inner mitochondrial membrane that transfer H+ across it, creating electrochemical gradient
• Complex I (NADH dehydrogenase) accepts two electrons from NADH and transfers them to coenzyme Q (ubiquinone)