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Mechanisms of Proton Pumping and ATP Synthesis

Explore electron transport chain complexes, proton pumping mechanisms, and ATP synthesis in the mitochondria, including key proteins, prosthetic groups, and the F0F1 ATPase structure. Learn how protons are pumped and electrons are transferred for energy production.

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Mechanisms of Proton Pumping and ATP Synthesis

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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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