Agbas (OxPhos) Flashcards
Ultrastructure of Mitochondria
- Two membranes: Outer (permeable: porin) and Inner (impermeable, metabolite transporters, cristae)
- Two compartments: intermembrane space and matrix (TCA Cycle and FA Oxidation)
- OXIDATIVE PHOSPHORYLATION occurs in INNER MEMBRANE
Where does Oxidative Phosphorylation occur?
Inner Membrane of the mitochondria
Oxidative Phosphorylation Overview
- TCA generates NADH and FADH2 –> high energy electrons flow through Electron Transport Chain (ETC)
- ATP synthase allow protons to return to matrix = ATP synthesis
Successful Oxidative Phosphorylation must accomplish what 3 things?
- transfer electrons from NADH/FADH2 to O2
- establish proton gradient across inner mitochondrial membrane
- synthesize ATP
Electron Transport Chain Components
Respirasome (Complex I, III, IV) –> pump protons
1) NADH Q oxidoreductase
3) Q cytochrome c oxidoreductase
4) cytochrome c oxidase
- Complex II: Succinate Q reductase; uses FADH2
- Complex II does NOT pump protons
Mobile Electon Carriers (2)
- Coenzyme Q (ubiquinone)
- transfers electrons from complex I/II to complex III - Cytochrome C
- shuttles electrons from complex III to complex IV
- final component of ETC
- catalyzes reduction of O2
Complex I
- NADH dehydrogenase or NADH-Q oxidoreductase
- first point of entry of electrons from NADH
- iron sulfur clusters: role in reduction rxns, proteins do NOT give up protons
Complex II
- Succinate-Q reducatase
- FADH2 enters ETC (Connects TCA to Oxphos)
- does not pump protons, less ATP synthesized from oxidation of FADH2
Complex III
- Q cytochrome C oxidoreductase
- passes electrons from QH2 to cytochrome C
- flow of electrons leads to transport of 2 protons to cytoplasmic side
Complex IV
- Cytochrome C oxidase
- catalyzes transfer of electrons from reduced Cyt C to molecular oxygen, the FINAL ACCEPTOR
- makes reactions aerobic, makes humans breathe
- 4 electrons funneled to oxygen to reduce it to water
- 2 heme and 3 copper
Free Radicals
- partial reduction of O2 generates high reactive oxygen derivatives, called reactive oxygen species (ROS)
- superoxide ion, peroxide ion, hydroxyl radical
- Normal Production: signaling (growth, hormone synth, inflammation)
- Over Production: damage to DNA, proteins, lipids
Antioxidants (2)
- Superoxide Dismutase (SOD) –> forms O2 and H2O2
- Catalase –> H2O2 to O2 and 2 H2O
EX: glutathione peroxidase, Vit-E, Vit-C
Mechanism of Action of SOD
- SOD1: Cu/Zn SOD –> cytosolic
2. SOD2: Mn/Zn SOD –> mitochondrial
Proton Motive Force
- two factors constitute a proton motive force to drive ATP synthesis by Complex V
- pH gradient
- Membrane potential
Chemiosmotic Hypothesis
- ETC moves protons across inner membrane as electrons flow from one complex to the next
- ATP synthase uses proton motive force to phosphorylate ADP
- If membrane disrupts, proton motive force cannot be established, and ATP synthesis does NOT occur
ATP Synthase
- in inner membrane (ball and stick structure)
- F0 subunit: stick, has proton channel
- F1 subunit: ball (into matrix), catalytic domains
- only B subunit of F1 is catalytically active
- a/B subunits arranged in hexameric ring (y and epsilon above as stalk)
- form dimers that form oligomers (stabilize molecules to rotational forces of catalysis)
- MAINTAIN CURVATURE OF INNER MEMBRANE
Cristae
allow the proton gradient to be in close proximity to the ATP synthase
ATP Synthesis
- 1 mol of ATP requires 3 + 1 H passage
- oligomycin disrupts proton transport through the channel
ATP-ADP translocase
- in outer/inner mito-membranes, works with mitochondrial carriers
- Flow of ATP and ADP coupled (ADP enters matrix only if ATP leaves)
- COMPLEX VI
NADH2 Shuttle Systems
- Malate-Aspartate Shuttle - oxaloacetate –> malate –> a-ketoglutarate (w/aspartate)
- COMPLEX 1 - Glycerophosphate Shuttle - G3P –> DHAP
- CoQ
Malate-Aspartate Shuttle
- heart, liver, kidneys
- generates NADH in mito-matrix
- NADH enters ETC at COMPLEX 1
Glycerophosphate Shuttle
- skeletal muscle, brain
- generates FADH2 in inner mito-membrane
- FADH2 joins ETC at CoQ
Inhibition of OxPhos
- when transfer of electrons inhibited = dec. in proton pumping, proton gradient and inhibition of ATP synth
Uncoupling and Heat Generation
- used to generate heat and maintain body temperature (uncouple OxPhos from ATP Synth)
- in brown adipose tissue
- UCP1: thermogenin (uncoupling protein) –> transfer protons from cytoplasm to matrix side (heat)
- UCP2/UCP3: energy homeostasis
Complex I inhibitors (4)
- amytal
- rotenone
- myxothiazol
- piericidin A
Complex II inhibitor
- malonate
Complex III inhibitor
- antimycin
Complex IV inhibitor
- CO, cyanide, H2S
Complex V inhibitor
- oligomycin
