Electron transport chain

• The hydrogens from glycolysis, the link reaction and the Krebs cycle are carried by the coenzymes NAD and FAD into the final stage of aerobic respiration
• The energy possessed by the hydrogen atoms are an important source of potential energy
• The electron transport chain is the mechanism by which the energy of the electrons within the hydrogen atoms is converted into adenosine triphosphate
• The electron transport chain

  • formation of ATP here is by oxidative phosphorylation because oxidation reactions are involved
  • In the presence of oxygen, energy is released to allow phosphorylation of ADP
  • Hydrogen atoms are split into protons and electrons
  • It requires reduced NADs, reduced FADs, electron carrier and oxygen to accept the electrons and protons at the end
  • Most energy is used to synthesise ATP, but some is lost as heat
• 1 molecule of reduced NAD produces 3 ATPs

  1 molecule of reduced FAD produces 2 ATPs
• Process of oxidative phosphorylation and chemiosmosis

  1. Coenzymes release hydrogen, which splits into protons and electrons
  2. The electrons pass along the electron carriers in a series of redox reactions, losing energy
  3. This energy pumps protons from the mitochondrial matrix into the intermembrane space, creating an electrochemical gradient
  4. At the end of the chain, electrons combine with oxygen and protons to form water
  5. Protons flow back into the mitochondrial matrix through ATP synthase, catalysing the formation of ATP
• The importance of oxygen

  • Oxygen is the terminal electron acceptor
  • Electrons cannot pass along the electron transport chain without oxygen
  • Accepts protons from mitochondrial matrix and electrons from the reduced electron carriers
• Alternative respiratory substrates

  • Lipids and proteins can also be used as respiratory substrates
  • Their breakdown products can be modified and used in the Krebs cycle depending on the number of carbon atoms they contain