Flashcards
Oxidative Phosphorylation
Cards in this deck (26)
- 1ATP synthesisRecycling from ADP central to live
Via oxidative phosphorylation in non-photosynthetic
Transfer of electrons from NADH to oxygen pumps protons across membrane, flow back down drives ATP synthesis - 2Energy transductionOxidation and phosphorylation coupled by proton gradient
Energy transduction of redox chemical chemical energy to bond chemical energy
In photosynthesis, energy transduction when light energy converted to chemical energy - 3Chemiosmotic theoryPeter Mitchell 1961
Difference in redox potential between reductant and oxidant (light energy or oxidation by oxygen)
Internal membranes with ETC - electron spontaneous movement via redox
Hydrogen pumped across, form PMF
Drives protein back through ATP synthase - 4In eukaryotes, occurs in mitochondriaPorous outer membrane and highly folded inner membrane
CA cycle in matrix, OP on inner membrane
Processes generating FADHS and NADH close to this
4 major complexes transfer electrons from carriers to O2. 3 use energy released to pump protons
Large release of free energy drives process of flow through electron carriers - 5Electron carriersUbiquinone
Cytochrome C - 6UbiquinoneQuinone dirivative with tail of isoprene units
Hydrophobic - diffuse rapidly in inner membrane
Carries electrons from NADH and FADH2 to complex III
2 kept groups hence 3 oxidation states - 7Cytochrome CHaem prosthetic group
Water soluble
Cytoplasmic side of membrane - 8Complex ISeries of components with intermediate redox potentials - enter at complex I
When NADH binds
2 electrons transferred to flavin mono nucleotide prosthetic group
Generates FMNH2
Electrons are transferred to series of iron sulphur clusters then ubiquinone
Flow of electrons result in 4H+ being pumped from matrix and 2 protons uptakes to generate QH2 to move to complex III - 9Complex IIFADH2 from CA cycle provides electrons
Enzyme part of CA cycle
Succinate Q reductase embedded in inner membrane
Electrons move to FeS clusters then to ubiquinone to generate QH2
No H+ pumping - lower ATP yield FADH2 than NADH - 10Complex IIIQH2 from complex I and II pass here - transfers electrons to cytochrome C using Q cucle
2 protons pumped across - only 2 as smaller thermodynamic driving force
Also contains cytochromes for electron flow within protein
Prosthetic groups located in region embedded in membrane - careful position for electron transport - 11The Q cycleQH2 passes 2 electrons to complex III, but cytochrome only able to accept 1
Temporary store of electrons in complex III protein
QH2 bind to complex III, 1 electron via FeS cluster then cytochrome prosthetic groups to cytochrome C to reduce
Second passes via ahem group to oxidised ubiquinone - generate semiquinone radical
Fully oxidised Q leaves, replaced by 2nd QH2 binding
Repeated to release 2 more protons and electrons, second electron reduces radical to generate QH2 and other taken up by cytochrome C
For every cycle, QH2 oxidised to Q and Q reduced to QH2 - 12Cytochrome C oxidase defines aerobic organismsComplex IV
Cytochrome C ancient protein with conserved canton - small, contains hame, loose association with inner mitochondrial membrane
Present in all organisms with mitochondrial respiratory chain and some prokaryotes
Evolved before divergence of animals and plants
1/4 amino acid residues invariant - 13Complex IVReduced cytochrome C diffuse from complex III
Protein catalyses transfer of electrons from cytochrome C to oxygen
Needs 4 cytochrome C to bind consecutively - 14MechanismElectrons from 2 reduced cytochrome C flow in electron transfer pathway in complex 4- one stops at CuB and another at heme 3
Oxygen bind to reduced ions and removes electron, forming peroxide bridge
2 more electrons flow from reduced cytochrome C to oxygen with 2 protons
Reduce ion-oxygen groups to ion OJ groups
2 more protons release 2 H2O molecules - 15Cytochrome C oxidase energyuses excess energy from reduction to pump 4 more H+ across membrane
Each reaction exergonic hence EC gradient made and used by ATPase - 16Link of OP and ATP synthesisFlow of electrons depend on 4 protein complexes and carriers
Efficiency varies
More complexes catalyse slower reactions - 17ATP synthesis mediated by ATP synthaseDiscovered through assaying activity in reverse
Initial though through high energy intermediate from ETC with phosphorylation transfer potential
Chemiosmosis -> electron transport and ATP synthesis coupled by proton gradient. Membrane impermeable to protons
PMF - unequal proton distribution-drives - 18PMFChemical gradient + charge gradient
200-300mV
In mitochondria, flow to equalise charge gradient
In chloroplast, pH gradient as charge gradient dissipated by counter ion movement - 19Evidence for Chemiosmotic TheoryElectron transfer initiation causes protons to be pumped out isolated mitochondria, detergents destroying inner membrane stop proton pumping and reverse it
Hydrophobic anions or basic abolish ADP phosphorylation - uncouple ET as dissipate PMF. Natural uncouplers = brown fat in hibernating form H+ channels to dissipate
Inhibitors of ATP synthesis also inhibit electron transfer and prevent O2 uptake
ATP can be produced in artificial membrane with only light dependent proton pump and ATP synthase - ETC and ATP separate, only linked by PMF - 20FFCPTRansport protons across membrane hence permeable to protons
- 21OligomycinBinds to Fo of ATP synthase
Prevents O2 uptake - 22ATP synthase structureProton conducting pore and catalytic unit
Ball (F1) and stick(F0) - most F0 in inner membrane
F1 has catalytic activity - can still produce ATP when isolated
F1 made of 6 polypeptides - 3 alpha and 3 beta in ring. Gamma changes conformation hexameter. also delta and epsilon transfer - 23ATP synthesisProton gradient doesn't synthesise ATP - removes from enzyme by causing rotation
Each alpha bind to ATP but doesn't take part
Central gamma alters conformation every 120 degrees - loose, tight, open - 24Loose, tight, open conformationsloose -> beta subunit binds to ADP and Pi
tight -> binds ATP tightly, ADP and PI consumed
Open -> release ATP - 25Regulating ATP synthaseControl reverse reaction - would cause wasteful hydrolysis if no PMF/ reversed
Could exhaust ATP quickly
Regulatory mechanisms suppress activity when no OMF - inhibition depends on organism e.g. plants stop at night hence strong - 26Use of reverse reactionTransmembrane protein pumping by ATP hydrolysis
Anaerobic bacteria - ATP used to generate PMF for ion transport and flagella movement
Inhibition weak as ATP synthase main generator of PMF
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- Biology of Cells IA (Chemistry of Life) Flashcards on Oxidative Phosphorylation, created by Alice Hathaway on 10/01/2019.
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