Flashcards
Lecture 20 PMB
Cards in this deck (32)
- 1chemoorganotrophs vs chemolithotrophs vs phototrophs1) obtain energy from organic compounds
2) obtain energy from inorganic compounds
3) obtain energy from sunlight
--> all must use ATP and the proton motive force - 2two types of phototrophyType 1) Light-sensing rhodopsins (containing retinal) directly pump protons through membrane, used by photoHETEROtrophs
Type 2) Photosynthetic reaction centers (containing bacteriochorophyll) indirectly pump protons through membrane, used by all photoautotrophs and some photoheterotrophs - 3What are the two types of reactions a photoautotroph performs?The light reaction (light energy --> ATP and NADH) AND dark reaction (chemical energy and NADH --> CO2 reduced to organic compounds
- 4Redox Equation of PhotosynthesisCO2 + 2H2A ----> (CH2O) + 2A + H2O
*in presence of light energy!* - 5e- Acceptor and Donor of Oxygenic PhotosynthesisAcceptor = CO2
Donor = Water
"A" = O - 6What organisms perform oxygenic photosynthesis?plants, algae, and cyanobacteria do this type of photosynthesis
- 7e- Acceptor and Donor of Anoxygenic PhotosynthesisAcceptor: CO2
Donor: H2S or someother reduced chemical
"A" = S or etc - 8What organisms perform anoxygenic photosynthesis?purple bacteria, green sulfur bacteria, heliobacteria perform this type of photosynthesis
- 9Oxygenic vs Anoxygenic PhotosynthesisSimilarities: both processes use light to generate PMF (aka energy!)
Differences: reducing power H2O or H2S, only one oxidizes water to oxygen, RCs contain chlorophyll or bacteriochlorophyll
--> just see whether or not the process produces oxygen - 10chlorophyll vs cytochromesBoth are porphyrins, but chlorophyll has Mg at center and heme/cytochromes have Fe
- 11Photosystem I (PSI)first stable electron acceptor is an Fe/S cluster in a protein
Fe/S-type RCs
used individually to generate PMF/reducing power, used with other to do oxygenic photosynthesis - 12Photosystem II (PSII)first stable electron acceptor is a quinone
Q-type RCs
used individually to generate PMF/reducing power, used with other to do oxygenic photosynthesis - 13Step Summary of Photosynthetic Electron Transport1) Light energy excites chlorophyll --> lowers the reduction pot. of chlorophyll --> reduces intermediate electron acceptor
2) e- flow downhill to more positive E0′
3) e- transport coupled to PMF
4) at 1st stable e- acceptor that has E0′ greater than NAD+ --> reverse electron flow occurs, generates reducing power (NADH) - 14e- flow in anoxygenic photosynthesis (purple bacterium)chlorophyll P870 absorbs light, converts to excited state P870* --> donates e- to next acceptor --> undergoes cyclic e flow to generate PMF or goes off path to generate reducing equivalents
*if non cyclic path, an e- must enter from a donor (in reverse to NAD+) to reduce original P870 pigment, at expense of PMF* - 15cyclic electron transport machinery in a purple bacteriumlight hits bacteriochlorophyll complexes; RC is where P870 is excited; PMF generated at the e- passing through a quinone pool; cytochromes and Fe-S pools pass electrons back to start
- 16purple bacteria vs green sulfur bacteria vs heliobacteria e- transportall use diff specialized chlorophyll pigments that get excited (P870, P840, P798);
(Because using PSII) reverse e- flow in purple bacteria generates NADH, whereas green sulfur and heliobacteria have Fe/S cluster (PSI) as first stable acceptor (lower in E0' than Fd) so they can both directly reduce Fd + use as e- donor in CO2 fixation - 17e- flow in oxygenic photosynthesis (The Z Scheme)light energy excites P680 to P680* --> e- reduces Ph subunit of PSII --> reduces mobile PQ --> PQ donates e- to cyt bf and releases proton to periplasm --> cyt bf passes e- to PC, more protons pumped out --> e- delivered to RC of PSI --> P700 excited to P700* --> e- passed to FeS and then reduces Fd protein
- 18Two options for e- flow in oxygenic photosynthesisNoncyclic-photophosphorylation: e- passed to flavoprotein, reduces NAD+/NADP --> generates PMF and reducing power
Cyclic-photophosphorylation: e passed to Fd and then RETURNS to cyt bf, travels to PSI using light energy --> generates PMF ONLY, used if reducing power is plentiful - 19pH of Stroma vs LumenStroma = high pH
Lumen = low pH - 20what protein returns oxidized P700 to ground state?in PSI, plastocyanin (PC) that passes on e-
- 21what returns oxidized P680 to ground state?in PSII, splitting of water that passes on e-
- 22what total protons are pumped through membrane for oxidative phototrophy?12H+ total
(turned into 2-3 ATP and reduces 2NADP+ 2NADPH) - 23total quanta of light required for phototrophyeach RC requires two quanta to run one e- through z scheme --> 8 TOTAL quanta of light needed
this total will allow for incorporation of one molecule of CO2 into an organic molecule - 24what pathway carries cyanobacterial PSII monomer to membrane?SrP pathway due to the fact that the protein is so hydrophobic
- 25Where is the photosynthetic system located?Cyanobacteria: within thylakoid membranes
Green Sulfur Bacteria: within chlorosomes
Heliobacteria: within the cytoplasmic membrane itself - 26Three Classes of Light Harvesting Pigments1) Chlorophylls
2) Phycobilins
3) Carotenoids - 27chlorophyllsdifferent chlorophylls absorb at different max wavelengths (depending on what protein chlorophyll is bound to)
organisms with one type of chlorophyll may be in a very different environment if they absorb at a much lower/higher wavelength - 28Phycobilinsspecific to cyanobacteria, function as the main light-harvesting antenna
red pigment = phycoerythrin = 550nm
blue pigment = phycocyanin = 620nm
absorbs at shorter wavelengths than chlorophyll --> e- can flow downhill from phycocyanin to chlorophyll a - 29CartenoidsALWAYS found in phototrophic organisms
absorbs blue light, transfers energy to RCs
has photoprotective role by quenching toxic oxygen species (anti-oxidants) - 30LH1 and LH2 of purple bacteriaH2, LH1, and RC packed in rings in cytoplasmic membrane
energy is transfer between pigments to chlorophyll --> charge separation occurs
quinone reduced by the RC diffuses to other areas of the membrane for e- transport and proton pumping. - 31Chlorosomes of green sulfur bacteriachlorosome: crystalline arrays of bacteriochlorophylls within a protein-lipid monolayer
excitation energy transferred from Bch through intermediate proteins/pigments to RCs (light or dark brown) - 32Phycobilisomes in Cyanobacteriaattached to thylakoid membrane, transfer light energy to PSII RC
phycoerythrins absorb highest energy photons, pass energy on successively to pigments that absorb LOWER wavelengths
energy reaches P680 of PSII and excites it