something cool
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CH339K. Something Cool. Wooly Mammoth – Mammuthus primigenius. Disappeared about 10,000 BC Frozen remains found periodically Wooly mammoth hemoglobin reconstructed Campbell, K.L. et al.(2010 ) Nature Genetics Advance Online Publication. Structure. - PowerPoint PPT PresentationTRANSCRIPT
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SOMETHING COOLCH339K
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Wooly Mammoth – Mammuthus primigenius
• Disappeared about 10,000 BC• Frozen remains found periodically• Wooly mammoth hemoglobin reconstructed• Campbell, K.L. et al.(2010) Nature Genetics Advance Online
Publication
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Structure
• Asian elephant (left) and mammoth (right) deoxyhemoglobin with BPG (chimeric molecule)
• Blue = location of mammoth mutations• Yellow = positive residues on b-chain
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Typical hemoglobin
Increasing temperature shifts binding to right
Blood entering warm, exercising muscles unloads more O2.
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O2 Binding Curves: Mammoth vs. Asian Elephant
• Intrinsic O2 affinity of mammoth Hb is 2 that of modern elephant
• In the presence of normal cofactors, the two are essentially identical• Increased cofactor affinity, however, reduces temp effects on O2 binding
• Mammoth Hb spec\ialized to deliver O2 to tissues whether cold or hot• Same adaptation seen in reindeer, musk oxen
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PHOTOSYNTHESISCH339K
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6CO2 + 6 O2 ⇄ C6H12O6
• Requires energy (big surprise)• Provided by radiation• 1017 kcal/year (1010 tons of
carbohydrate produced - 2 tons/person)
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Chloroplasts will reduce an artificial electron acceptor when illuminated
Hill Reaction
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hE Where h = 6.626 x 10-34 Jsec
And n = frequency (NOT wavelength)
For cyan-colored light, this works out to ~ 240 kJ/mol photons
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Absorption of light
• Internal conversion - electronic energy converted to heat, time frame < 10-11 s
• Fluorescence - excited state decays to ground state by emitting photon, time frame ~10-8 s
• Exciton transfer (resonance energy transfer) – excited molecule transfers its excitation energy to nearby unexcited molecules, important in funneling light energy to photosynthetic reaction centers
• Photooxidation - light-excited donor molecule transfers an electron to an acceptor molecule, the oxidized donor relaxes to ground state by oxidizing some other molecule
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Chlorophyll is assembled in light harvesting complexesExample shown contains
Chlorophyll A (green)Chlorophyll B (red)Lutein (yellow)
Chlorophylls and accessory pigments harvest incoming photons and are excited
Energy is passed on through exciton transfer to a reaction center
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Need 2 e- to reduce the quinone
Pheo = pheophytinQ = quinone
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Rhodospirillum action center1) Excited chlorophyll passes electron to pheophytin2) Electron then passed to menaquinone3) Electron passed through Fe to ubiquinone QB 4) Cytochrome donates electron back to action center chlorophyll
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Green sulfur bacteria also have a non-cyclic system that passes electrons through ferridoxin to NADPHFerridoxin is an iron-sulfur proteinBelow is ferridoxin 1 from AzotobacterContains one [4Fe-4S] cluster and one [3Fe-4S] cluster
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Energetics
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Need 2 ferredoxins
Produces good reductant (Ch*) and strong oxidant (Z)
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Organization of Photosystem 1
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Cytochrome b6f Complex
• Proton pump• Transfers electrons to Plastocyanin (carrier to PS1)• As is complex 3 of ETC, electrons from QH2 have to cycle through one at a
time
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Ubiquinone
Plastoquinone
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To fix 1 CO2 requires: 2 NADPH molecules 3 ATP molecules
• Each molecule of oxygen released by the light reactions supplies the 4 electrons needed to make 2 NADPH molecules.
• 4 electrons passingthrough cytochrome b6/f complex provides enough energy to pump 12 protons into the interior of the thylakoid.
• To make 3 molecules of ATP, the ATPase in chloroplasts needs about 14 protons (H+)
Deficit is made up by cyclic photophosphorylation. • Electrons expelled by the energy of light absorbed by photosystem I pass, as
normal, to ferredoxin (Fd). • Then pass to plastoquinone (PQ) and on back into the cytochrome b6/f
complex. • Here each electron liberates pumps 2 protons (H+) into the interior of the
thylakoid — enough to make up the deficit left by noncyclic photophosphorylation.
Cyclic Photophosphorylation
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Splitting Water
Complex associated with PS II uses several Mn ions to extract 4 electrons from 2 water molecules.P680 is rereduced by Tyrosine in the PSII reaction centerTyrosine radical is rerreduced by increasing oxidation state of a Mn clusterWhen Mn cluster reaches +4 state, it can grab 4 e- from 2 H2O
e- source for PS II