1. Lecture 5 Proton Pumping and ATP Synthesis Mechanisms

2. Electron Transport Chain

3. 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, Q 10, etc UQ is very hydrophobic –Lives in inner mitochondrial membrane UQ picks up Hs from Complex I and becomes reduced UQH 2 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 F 0 F 1 ATPase Structure The F 0 channel is composed of 12 cylindrical proteins –These rotate as protons enter F 0 When  subunit of F 0 rotates, it causes  subunit of F 1 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