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Ox Phos
Biochem and medical genetics
| Question | Answer |
|---|---|
| Mitochondrial structure | Double membrane Relatively permeable outer membrane due to large porin channels Highly impermeable inner membrane with highly specific transporters Internal cristae structures to increase surface area Internal matrix space |
| What do mitochondria contain enzymes for | ETC TCA cycle PDH B oxidation Ketone body metabolism Urea cycle Not all present in all mitochondria - tissue specific |
| Processes of oxidative phosphorylation | Couples two main processes 1 - generation of a proton gradients by oxidising H carriers, transporting electrons, consuming oxygen and producing water 2 - ATP synthesis using proton gradient to phosphorylate ADP |
| Chemiosmotic theory - Mitchell | Movement of electrons drives proton pumping These protons are pumped from the matrix to the IMS Creates electrical and pH gradient across the highly impermeable inner membrane Protons move down gradient through ATP synthase |
| What is the ETC | 4 large complexes - each with many proteins Complex 1 - 4 Linked by 2 small mobile electron carriers Ubiquinone - Complex 1 and 2 to 3 Cytochrome C - Complex 3-4 |
| What does the ETC need to transfer electrons | Oxidation/reduction reactions with increasing redox potential to pass electrons from NADH/FADH2 to O2 A way of facilitating single and double electron transfer |
| Types of groups used in electron transfer | Iron in Iron-sulphur clusters - complex 1, 2, 3 Iron as Haem in cytochromes - Complex 3 and 4 as well as cytochrome C Copper - complex 4 |
| Complex 1 | Uses HADH as substrate - freely diffusible in matrix 2 electrons pass through complex 1 to Flavin mono nucleotide, reducing it to FMH2, then to a series of FE-S clusters Electrons to ubiquinone along with 2 H from matrix Pumps 4 protons into IMS |
| Structure of Complex 1 | Transmembrane region involved in proton pumping Matrix region involved in electron moving, oxidation of NADH and iron sulphur chain |
| Complex 2 | Uses FADH2 as substrate - physically linked to succinate dehydrogenase 2 electrons passed from FADH2 to a series of FE-S clusters Electrons passed to Q along with 2 H from matrix No proton pumping - not enough energy stored in FADH2 No communication |
| Ubiquinone | Known as Co-Enzyme Q10 Long hydrocarbon tail makes it highly hydrophobic Retained in inner membrane, moving within the hydrophobic phospholipid environment Can accept 2 electrons from complex 1 or 2 to produce QH2 |
| Complex 3 | Uses Q as a substrate - produces 2 cytochrome C Needs to accepts 2 electrons at once but release them one at a time without leaving electrons in the matrix unbound contains 3 cytochromes, Rieske protein Performs Q cycle |
| Q cycle | QH2 arrives - 1 electron to Rieske protein and straight to cytochrome C Other binds to Cyt b and is transferred to Q to form a semi-quinone radical Second QH2 binds - one electron to cytochrome C Other to Cyt b then to the semi-quinone radical |
| Proton movement at complex 3 | Generates power to pump 4 protons into IMS |
| Cytochrome C | Transports 1 electron from complex 3 to 4 Water soluble, so resides at the periphery of membrane closer io intermembrane space Contain haem prosthetic group |
| Complex 4 | Uses cytochrome C and O2 as substrates Generates H2O O2 is terminal electron acceptor Electrons flow between haem and copper O2 form peroxide bridge between terminal haem and copper 4 H pumped |
| Electron flow in complex 4 | 2 cytochrome C arrive - 1 electron to CuB and other to Haem a3 O2 forms peroxide bridge between them Another 2 cyt C arrive - each donate an electron to the bridge Addition of 2 protons forms OH groups More protons form H2O The products are halved |
| Structure of phosphorylation apparatus | Phosphate carrier ATP synthase ANT Porins |
| Phosphorylation | The proton gradient is used to power a motor that phosphorylates ADP to ATP The H gradient provides the intermediate that couples oxidation by ETC to phosphorylation Done by ATP synthase |
| ATP synthase | Protons flow through F0 subunit - drives rotation of the y subunit via conformational changes y subunit rotation drives F1 subunit conformational change that drive phosphorylation of ADP |
| F0 subunit | Protons enter through subunit a Binds to aspartate residues in c subunit which neutralises the amino acids charge causing it to rotate This drives rotation of y subunit Linked to F1 portion |
| F1 subunit | B subunits catalyse ATP synthesis Each is conformationally different - open, loose or tight Open - ADP and Pi enter ATP leaves Loose - held in place Tight - synthesises ATP Rotate between phases by y subunit rotation |
| Evidence - Boyer and Walker | Turned AT synthase upside down and attached to a membrane Attached actin filament to y subunit Cam visualise movement when proton gradient generated |
| Adenine nucleotide translocase and phosphate carrier | Use the proton gradient as well Make the inside more positive by discharging electrochemical gradient Take protons from ATP synthase |
| Evidence | Mitochondria alone and mitochondria with substrate consume little oxygen Mitochondria only consume oxygen when stimulated by ADP which drives oxphos Mitochondria stop consuming oxygen what all ADP is phosphorylated Chemical inhibitors at any point |
| Thermogenesis | Occurs mostly in brown adipose tissue in newborn and hibernating animals Uncoupling protein 1 expressed in these cells Dissipates the proton gradient independently of ATP synthase, resulting in non-shivering heat generation Uncouples oxphos |
| Dinitrophenol | A lipophilic weak acid that can cross the inner membrane and dissipate the proton gradient - chemical uncoupling Electron transport and oxygen consumption continue uncontrolled but phosphorylation stops Leads to hyperthermia etc Cannot be reversed |
| AMP | Concentration usually 5nM Adenylate kinase only forms this under insufficient ATP Serves as an energy distress signal to the cell Activates AMP activated protein kinase, which upregulates energy generating pathways and suppresses energy consumption |
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