Lecture 20 PMB

Question	Answer
chemoorganotrophs vs chemolithotrophs vs phototrophs	1) 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
two types of phototrophy	Type 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
What 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
Redox Equation of Photosynthesis	CO2 + 2H2A ----> (CH2O) + 2A + H2O in presence of light energy!
e- Acceptor and Donor of Oxygenic Photosynthesis	Acceptor = CO2 Donor = Water "A" = O
What organisms perform oxygenic photosynthesis?	plants, algae, and cyanobacteria do this type of photosynthesis
e- Acceptor and Donor of Anoxygenic Photosynthesis	Acceptor: CO2 Donor: H2S or someother reduced chemical "A" = S or etc
What organisms perform anoxygenic photosynthesis?	purple bacteria, green sulfur bacteria, heliobacteria perform this type of photosynthesis
Oxygenic vs Anoxygenic Photosynthesis	Similarities: 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
chlorophyll vs cytochromes	Both are porphyrins, but chlorophyll has Mg at center and heme/cytochromes have Fe
Photosystem 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
Photosystem 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
Step Summary of Photosynthetic Electron Transport	1) 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)
e- 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
cyclic electron transport machinery in a purple bacterium	light 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
purple bacteria vs green sulfur bacteria vs heliobacteria e- transport	all 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
e- 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
Two options for e- flow in oxygenic photosynthesis	Noncyclic-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
pH of Stroma vs Lumen	Stroma = high pH Lumen = low pH
what protein returns oxidized P700 to ground state?	in PSI, plastocyanin (PC) that passes on e-
what returns oxidized P680 to ground state?	in PSII, splitting of water that passes on e-
what total protons are pumped through membrane for oxidative phototrophy?	12H+ total (turned into 2-3 ATP and reduces 2NADP+ 2NADPH)
total quanta of light required for phototrophy	each 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
what pathway carries cyanobacterial PSII monomer to membrane?	SrP pathway due to the fact that the protein is so hydrophobic
Where is the photosynthetic system located?	Cyanobacteria: within thylakoid membranes Green Sulfur Bacteria: within chlorosomes Heliobacteria: within the cytoplasmic membrane itself
Three Classes of Light Harvesting Pigments	1) Chlorophylls 2) Phycobilins 3) Carotenoids
chlorophylls	different 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
Phycobilins	specific 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
Cartenoids	ALWAYS found in phototrophic organisms absorbs blue light, transfers energy to RCs has photoprotective role by quenching toxic oxygen species (anti-oxidants)
LH1 and LH2 of purple bacteria	H2, 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.
Chlorosomes of green sulfur bacteria	chlorosome: crystalline arrays of bacteriochlorophylls within a protein-lipid monolayer excitation energy transferred from Bch through intermediate proteins/pigments to RCs (light or dark brown)
Phycobilisomes in Cyanobacteria	attached 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

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	Created by Candice Young over 6 years ago