Fichas
Photosynthetic Metabolism
Fichas del conjunto (38)
- 1Importance if metabolismAllows cells to survive and ecosystems to develop
Redox reactions drive metabolism, ETC made of mobile carrier and membrane protein complexes
Flexible and responds to environment - 2Ways of gaining energyPhotoautotroph
Chemoautotroph
Heterotroph
All have similar core metabolic pathways hence from common ancestor - 3Complex pathways unified byBiochemical building blocks
Energy stores
Carrier molecules
Regulatory proteins - 4Redox reactionsSplit into half reactions
Those with more negative potentials donate electrons, accepted by those more positive - 5Yeast fermentationSugars from barley
Thermodynamically favourable to produce 2ATP
Glucose -> pyruvate. Produce 2NADH
Won't proceed without ADP or NAD+ - 6Regulation of fermentationUnder anaerobic conditions
Gene expression - enzyme expression reduced if on non-fermentable carbon source - 7Why reduced ATP yield of glucose?Glucose only partially oxidised hence still energy rich
Different in reduction potential between primary donor and terminal acceptor relatively small - 8What is external electron acceptor used?All carbon fully oxidised to release maximal energy
To allow electron transfer, requires electron carrier and ETC - 9NADPH and FADH2Similar redox carriers
FADH2 embedded within proteins - not mobile carrier - 10Electron Transport Chain StructureTerminal electron donor and acceptor
Transmembrane complexes containing electron carriers
Mobile carriers to transport electron between complexes
Electron or hydrogen - 11Theory of ETCPMF created to generate ATP by chemiosmosis
Mobile electron carriers
Mobile hydrogen carriers
Large transmembrane protein complexes - 12Mobile electron carriersSmall proteins
transition metals to carry electron directly - 13Mobile hydrogen carriersOrganic
Carry electron only if undergo chemical reaction involving protons
plastaquinone and ubiquinone - 14Large transmembrane protein complexesMultiple protein subunits
Omternal electron acceptors
Quinones, haem groups, chlorophyll, FeS clusters
Complex II in mitochondria contains haem, 3FeS and FAD - 15Use of ETC regulated and flexibleChemolithotrophic Bacteria in biomining
Mineral ores rich in precious metal in sulphite form insoluble hence expensive to extract
Source of Fe3+ act as oxidising agent on sulphite, release as soluble sulfate - extracted by other processes
Bacterium provides Fe3+ through ETC - 16Metabolic flexibility in Chemolithotrophic BacteriaATP synthesis = Fe2+ oxidised in outer membrane on cytochrome C, forming Fe3+. Periplasmic electron carrier proteins transfer e to cytochrome C oxidase. Transferred to O2 as terminal acceptor
NAHD synthesis = ATPase turned off and PMF transport electrons through complexes and carriers in reverse electron flow to produce more NADH
Can switch between pathways - 17Challenges for harvesting lightIndividual chlorophyll only max 10 photons/ second
Water inert, but supplies electrons for ETC
Transfer of electrons from water to NADPH needs complex ETC - 18Photosynthetic organismsPlant, algae, cyanobacteria
Green algae - unicellular/ fast growth/ motile/ can mutate and transform/ eyespot detect light/ single chloroplast. Can switch between photosynthetic and heterotrophic growth - 19Chlorophyll light absorptionSolves thermodynamically unfavourable reaction
Chl -> Chl* + A -> Chl+ + A- ->Chl
Light absorbed at Chl -> Chl* + A - 20Charge separationChl* + A -> Chl+ + A-
Only occurs if correct chemical environment
Can extract e from H2O
Key event converting light energy to chemical energy - 21ChlorophyllA (methyl) and B(formyl) absorb different wavelength - red and blue
Lipid soluble - position and orientation in membrane
Neither alone provides sufficient energy
Emerson Enhancement Effect -> work together to produce 200kjmol needed= - 22Z scheme2 inputs of energy (each photosystem)
Only place of photochemical events
All others thermodynamically unfavourable - 23Photosystem consists of light harvesting complex and reaction centre operating togetherElectron transfer 10^5 x quicker than light capture
only 2 of 36 do charge separation - "special pair"
reaction centre surrounded by light harvesting chlorophylls- absorb photons and pass energy to reaction centre through RET
fast and biophysical - no e move
99% efficiency
Acceptor really close to special pair hence can grab to move to ETC - 24Reaction centredimer of reaction centre chlorophylls in luminal side
Symmetry, but only 1 branch used
Precise arrangement of electron acceptors facilitate electron transfer
Light absorption in harvesting complexes in PII causes energy transfer to special pair in reaction centre by RET
Charge separation and photochemistry due to carefully positioned electron acceptors - 25Electron acceptors in PIIPheophytin and quinone
- 26Photosynthetic electron transport chainElectron transferred between internal electron carries in PSII reaction centre
Quinone B accepts 2e and 2H+ from stroma, released from PSII as PQH2. lipid soluble
PQH2 moves to cytochrome B6F complex - donates e and H+ move to lumen
Electrons passed to plastocyanin - take e to PSI to replace loss by charge separation
RET at PSI and charge reparation at reaction centre. Electron from P700 transferred to internal carriers inc. FeS clusters
Electrons passed from terminal FeS cluster to stroll ferrodoxin - 27Role of FerrodoxinFerrodoxin-NADP+ reductase catalyses transfer fo electrons from Fd to terminal electron acceptor, generating NADPH
- 283 challenges of carbon fixationLow atmospheric CO2 concentration
CO2 fixation coordinated with light capture
Enzymes carry out side reactions - 29Discovery of CBB cycleRadiative tracer - C
Placed algae in light then kill at intervals using boiling EtOH
Analyse with paper chromatography to see what present
1 = triose phosphate, PEP, PGA
2= sucrose/ sugars
3= organic acids - malic/ citric
4= amino acids - 30RuBisCORibulose Bisphosphate Carboxylase/ Oxidase
Kcat = 3CO2/ sec
Km = 10um CO2 (cell only 9um)
50% protein is RuBisCO as slow
Carbon fixation by rubisco
RuBP -> endiolate intermediate -> unstable intermediate -> 2 x 3-phosphoglycerate
8 large and 8 small subunits - active site in large subunit - 31The cycleCO2 fixation by rubisco- no carriers
Reduction of 3PGA to 3GAP - energy from ATP and NADPH needed
RuBP regenerated using ATP
Autocatalytic - self contained in use of carbon - 32Regulation of cycleCycle activated by light to ensure active when NADPH and ATP being made
Some enzymes redox regulates (sedoheptulose-1,7-bisphosphate)
Electrons from PSI reduce ferredoxin. Pass via thioredoxin to reduce inhibitory disulphide bridge to active enzyme
Oxygen evolving complex -> manganese cluster buffers redox change. Only when 4 flashes of light and completely oxidised will water be split - 33Side reactions of RUBISCOOxygenation
Misfire - 34OxidationForms 13PGA and 1 phosphoglycollate instead of 2 3PGA
Phosphoglycollate toxic hence rapidly metabolised by photorespiration
Occurs in chloroplast, mitochondria and peroxisome - metabolically costly as ATP used and CO2 release din mitochondria. NADH used and H2O2 used - less carbon fixed and some wasted - 35Misfire reactionsXuBP generated from RuBP
XuBP abhorrent product - damaged metabolite hence enters metabolite repair pathways XuBP inhibitor of RuBP - 36Repair PathwaysRome aberrant product and return damaged molecule back to original e.g. NADPX from spontaneous chemical or enzyme reactions
NADPH hydrate inhibits other enzymes, repair and remove R and S epimer in 2 part process
ATP dependent NADPX dehydrates reconverts S epiterase, epimerise interconverts R and S epimers - 37Pre emptionStop damage from unwanted metabolites occurring, rapid conversion of harmful to normal product
XuBP inhibits RuBiSCO- harm due to accumulation prevented by phosphate to convert to Xu5BP- normal part of CBB cycle - 38OverviewLife based on ATP adn electron and H+ carriers
ETC extract energy from biological molecules and store in ATP
Photosystems rely on chlorophylls in LHC and RC doing different things
Nothing of chemistry disappears in biology
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- (Chemistry of Life) Biology of Cells IA Fichas sobre Photosynthetic Metabolism , creado por Alice Hathaway el 09/01/2019.
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- Alice Hathaway
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