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Lecture 5

Lecture 5. Proton Pumping and ATP Synthesis Mechanisms. Electron Transport Chain. Electron Transport Chain. Electron Transport Chain (ETC) contains 4 complexes All complexes are embedded in inner mitochondrial membrane Each complex consists of many proteins

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Lecture 5

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  1. Lecture 5 Proton Pumping and ATP Synthesis Mechanisms

  2. Electron Transport Chain

  3. Electron Transport Chain • Electron Transport Chain (ETC) contains 4 complexes • All complexes are embedded in inner mitochondrial membrane • Each complex consists of many proteins • Structural - maintain shape of complex • Prosthetic group - transporter of H/e- • Proteins are arranged so that: • H+ expelling reactions on outside • H+ consuming reactions on matrix side • ~10 H+ are pumped out for each NADH

  4. NAD • Complex I takes H from NADH - reoxidize NADH to NAD • NAD is a dinucleotide - 2 nucleotides joined back to back • NAD likes to rip H off from –CH-OH groups • Converting them to -C=O groups • Nicotinamide = Niacin

  5. UQ (Ubiquinone) • Electrons move around in Complex I • from one prosthetic group to another (sometimes with protons, sometimes not!) until they reach UQ • a.k.a. coenzyme Q, Q10, etc • UQ is very hydrophobic • Lives in inner mitochondrial membrane • UQ picks up Hs from Complex I and becomes reduced • UQH2 transfers Hs to Complex III

  6. Cytochrome C (Cyt C) • Cyt C picks up e- from Complex III and gives the e- to Complex IV • Cyt C has a prosthetic group which contains an iron atom • Changes from ferrous to ferric as it loses and accepts the electrons • Does NOT carry hydrogens!

  7. Mechanism of Proton Pumping • When different types of carrier exchange Hs and e-, H+ can be taken up or released • The orientation of the uptake/release can allow net translocation (pumping • Proton releasing reactions on the cytoplasmic side • Proton consuming reactions on the matrix side

  8. FAD (Flavin Adenine Dinucleotide) • Present in Complex II • Acceptor of Hs • Likes to rip H from a saturated hydrocarbon chain • FAD is totally stuck in Complex II,  it cannot roam around like NAD

  9. Significance of F0F1ATPase Structure • The F0 channel is composed of 12 cylindrical proteins • These rotate as protons enter F0 • When g subunit of F0 rotates, it causes b subunit of F1 to change its structural conformation, which allows ATP to be made • Movement of 3 protons  generation of 1 ATP • ~10 H+ are pumped out for each NADH,  ~3 ATP from 1 NADH

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