Lectures 28-29 Oxidative Phosphorylation Flashcards
Which membrane of the mitochondria is permeable due to the presence of porin?
Outer membrane
Which membrane of the mitochondria is impermeable and relies on metabolite transporters?
Inner membrane
What component of the mitochondria is the site of TCA cycle and fatty acid oxidation?
Mitochondrial matrix
Where does oxidative phosphorylation take place?
Inner membrane of mitochondria
What are the 2 electron carriers involved in the electron transport chain?
Coenzyme Q/Ubiquinone, Cytochrome c
Coenzyme Q/Ubiquinone
Transfers electrons from Complexes I and II to Complex III (most common=COQ 10)
Cytochrome c
Shuttles electrons from Complex III to Complex IV; Final component which catalyzes reduction of O2 to H2O
What are the prosthetic groups for Complex I (NADH-Q oxidoreductase)?
FMN, Fe-S
What are the prosthetic groups for Complex II (Succinate-Q reductase)?
FAD, Fe-S
What are the prosthetic groups for Complex III (Q-cytochrome c oxidoreductase)?
Heme bH, bL, C1 and Fe-S
What are the prosthetic groups for Complex IV (cytochrome c oxidase)?
Heme a, a3, CUa and CUb
Name the oxidized form of coenzyme Q
Q, Ubiquinone
Name the reduced form of ocenzyme Q
QH2, Ubiquinol
Friedreich’s Ataxia
Mutation in Frataxin which helps synthesize Fe-S clusters; affects CNS/PNS/heart/skeletal system
Complex I of the ETC
First point of entry for electrons from NADH; L shaped with horizontal arm in inner membrane and vertical arm projecting into matrix; oxidizes NADH and reduces coQ; H+ moved to inner membrane from mito matrix
Complex II of the ETC
FADH2 enters here, does not leave complex; electrons from FADH2 are transferred to FeS and then to coQ to form QH2; DOES NOT PUMP PROTONS
Complex III of ETC
Passes QH2 electrons to cytochrome c; flow of electrons leads to transport of 2 protons to cytoplasmic side; QH2 is oxidized and Cyt c is reduced
Q cycle
Occurs in complex III; Passes one electron to cytochrome c, the other to a bound Q; Then another QH2 gives its electrons to a cytochrome c and the Q anion to form QH2
Complex IV of ETC
Last complex; transfers electrons from reduced cytochrome c to molecular oxygen = the final electron acceptor!
How many protons are transported by Complex IV?
4 pumped protons and 4 chemical protons
Partial reduction of oxygen forms what?
Free radicals
What are some pathological conditions that involve free-radical injury?
Parkinson’s disease, Ischemia; reperfusion injury
How do antioxidants defend against free radicals?
SOD: allows free H+ to convert oxygen radicals into oxygen and peroxide; catalase: breaks down peroxide into oxygen and water
Chemiosmotic hypothesis
The transport of protons from the matrix to cytoplasmic side of inner membrane generates a pH gradient and membrane potential which constitutes a protein motive force used to drive ATP synthesis
*Evidence: bacteriorhodopsin experiments
ATP synthase
Ball and stick structure embedded in inner membrane; F0 = stick with proton channel; F1=ball protruding into matrix an containing catalytic domains
What polypeptide chains of ATP synthase (F0 subunit) are catalytically active/constitute active site?
the beta subunits
How are the F0 and F1 subunits of ATP synthase connected?
- central gamma/epsilon stalk
2. exterior column of 1 alpha, 2 beta, 1 delta subunit
What is the function of ATP synthase?
Stabilizes molecules to rotational force during catalysis, maintains curvature of inner membrane
What is the role of the proton gradient?
Release ATP from the synthase
What is the function of the gamma subunit of ATP synthase?
Forms stalk, creates asymmetry in the structure, rotation causes the switch between L, T, O conformations
What are the three steps in ATP synthesis?
- Binding of ADP and Pi (L conformation)
- ATP synthesis (T conformation)
- Release of ATP (O conformation)
Proton conducting unit of ATP synthase
c subunit: 2 alpha helices that span membrane with aspartic acid in the middle; a subunit has cytoplasmic half-channel and matrix half-channel allowing proton to enter and pass partway (a subunit connects F0 and F1)
What drives the rotation of the c ring in the F1 subunit of ATP synthase?
Proton motion (neutralizes aspartic acid in the cytoplasmic subunit and allows rotation of c ring moving aspartic acid and eventually H+ out)
What powers each 360 degree rotation of the c ring and what does this rotation generate?
3 H+ power the rotation, which generates 3 ATP
Role of ATP-ADP translocase
Exchanges ADP and ATP across inner mitochondrial membrane as they are normally not permeable. ADP enters matrix only if ATP leaves
How is cellular respiration regulated?
- ATP via negative feedback
2. ADP (respiratory control): must have enough ADP to make ATP
How is ATP synthase regulated?
Inhibitory factor I - inhibits hydrolytic activity of ATP synthase as a protective inhibitor, preventing ATP breakdown
What are the proteins involved in uncoupling oxidative phosphorylation for the purpose of heat generation?
Thermogenin (UCP 1), UCP 2 and UCP 3 also involved
What inhibits ATP synthase?
Oligomycin (binds to c subunit)
What uncouples electron transport from ATP synthesis?
2,4-dinitrophenol (dissipates H+ gradient)
What inhibits ATP export by inhibiting ATP-ADP translocase?
atractyloside, bongkrekic acid
What inhibits Complex I of ETC?
rotenone, amytal
What inhibits Complex III of ETC?
antymycin A
What inhibits Complex IV of ETC?
CN-, N3-, CO
