chapter 20 biochem

• Electron-transport chain


  Also called respiratory chain, flow of electrons from NADH and FADH2 to O2

  
• Proton gradient


  Generated by the exergonic set of oxidation-reduction reactions, used to power the synthesis of ATP

  
• Oxidative phosphorylation captures the energy of high-energy electrons to generate ATP
• The electron-transport chain and ATP synthesis occur in the mitochondria
• The inner membrane, which is folded into ridges called cristae, is impermeable to most molecules.
• The outer mitochondrial membrane is permeable to most small ions and molecules because of the channel protein mitochondrial porin
• The inner membrane, which is folded into ridges called cristae, is impermeable to most molecules.
• The citric acid cycle and fatty acid oxidation occur in the matrix of the mitochondria

  
  

  the site of electron transport and ATP synthesis.
• The electron-transport chain is a series of coupled oxidation–reduction (redox) reactions that transfer electrons from NADH and FADH2 to oxygen
• A strong reducing agent readily donates electrons and has a negative E0

  A strong oxidizing agent readily accepts electrons and has a positive E0
• 3 protein complexes embedded in the inner membrane pump protons out of the mitochondria, generating a proton gradient
• NADH-Q oxidoreductase (Complex I) Q-cytochrome c oxidoreductase (Complex III) Cytochrome c oxidase (Complex IV)
• NADH-Q oxidoreductase (Complex I)

  Q-cytochrome c oxidoreductase (Complex III)

  Cytochrome c oxidase (Complex IV)

  succinate-Q reductase (Complex II)(delivers electrons from FADH2 to complex III)
• cytochromes are electron-transferring proteins that contain a heme prosthetic group. The heme iron cycles between Fe2+ and Fe3+ as it accepts or donates electrons.
• Iron-sulfur proteins, also called nonheme iron proteins, are prominent electron carriers
• Like cytochromes, the iron cycles between Fe2+ and Fe3+ as it accepts or donates electrons
• The electrons from NADH are passed along to Q to form QH2 by Complex I
• Four protons are simultaneously pumped out of the mitochondria by Complex I
• The FADH2 generated in the citric acid cycle reduces Q to QH2, which then enters the Q pool.
• Complex III contains two types of cytochromes named b and c1.
• Electrons flow from ubiquinol to cytochrome c through Q-cytochrome c oxidoreductase
• The mechanism for coupling electron transfer from QH2 to cytochrome c is called the Q cycle
• In one cycle of the Q-cycle, 4 protons are pumped out of the mitochondria and two more are put into the mitochondria
• Partial reduction of O2 generates highly reactive oxygen derivatives, called reactive oxygen species (ROS).
• Superoxide dismutase (SOD) and catalase help protect against ROS damage