L20: Phototrophy and Sulfur Flashcards
What do photosystems do
absorbs photons and use it to energise e-s
Describe energy levels for PS2 + 1
PS2: -0.4 redox potential => +1.2 ox potential (very oxidising, splits water)
PS1: -1.2 =>0.6
Distinguish between short vs long wavelengths
short = more energy
Long = less energy
What is PS2’s job, what is the equation
pulls e- from water and release O2
H2O(e-donor) = 2H+ + 2e + O2
the PS pigments are reduced as e- donors are oxidised HUH
PS2 steps
- ps2 harvest short, high-energy light
- light energy transfered to e-, raised to higher energy levels making them highly electronegative
- e- falls along e- carriers, given to PS1
- the fall yields energy =>making H+ pumped across membranes thereby feuling H+ gradeint
- this in turn fuels ATP synthesis and ATP fuels CO2 fixation
PMF
proton motive force (H+)
PS1
- e- passed here then PS1 absorbs more light energy
- light energy causes e- on reduced pigments to be raised more
2 paths next cyclic and non cyclic;
noncyclic: falls tot the ETC, directly reduce NADP+ to NADHPH which is reducing power, this consumes e- donor molecules => noncyclic
cyclic:falls between PSs, falling along carriers yeilds energy => H+ pumped across the membrane
Describe cyclic vs non cyclic electron flow (oxygenic)
noncyclic: falls tot the ETC, directly reduce NADP+ to NADHPH which is reducing power, this consumes e- donor molecules => noncyclic
cyclic:falls between PSs, falling along carriers yeilds energy => H+ pumped across the membrane
Explore Anozygenic Microbial photosynthesis, what does this reveal
- the process does not produce O2
*they harvest longer wavelengths flight compared to cyanobacterial oxygenic phototrophs, however, longer wavelengths = less energy
*the photosystems are not strong enough to oxidise H2O as the e-donor they need other e-donors, that is why O2 is not yielded
*In dark conditions, species use other carbon sources meaning NOT all bacteria rely on CO2 for carbon fixation
What are the conditions of anoxygenic electron flow
- depends on species, environmental conditions, electron donors, type of bacteria
*also largely depends on the type of bacteria (green v purple) and oxygen availability
*can be cyclic or non-cyclic
*both or one can happen in a species
What is the end product of anoxygenic electron flow
yields ATP
Explain the mechanism behind cyclic e- flow in anoxygenic phototrophs
*low energy e- go from cytochrome to bacteriochlorophyll of the PS [recyling them], reducing the photosystem
*light energy absorbed by pigrments of the reduced PS is transfered to the e-s, which raises them to higher energy levels
*the high energy es fall along e- carriers, releasesing energy as they fall back to the PS
*H+ are pumped our of the cell using the energy from the fall
*this generates H+ gradient that fuels ATP synthesis
*the e- are now low energy and are recycled to the PS again, reducing it
*the e-s are not list to NADPH so there is no consumption of e- donors, cyclic
Explain noncylic e- flow in anoxygenic phototrophs
*non cyclic e- flow consumes e- from e- donors, these donors are H2S, So, H2, organic compounds
*GS and PS bacteria are more dependant on sulfur products
*GNSB and PNSB are more not as dependant on fulfur
*cells can make NADH or NADPH and they interchange e- to balance NADH:NADPH [all of them do that last part]
Contrast the key different between S and NS bacteria
non sulfure bacteria tend to be more sensitive to H2S
S can accumilate So
Draw the sulfur cycle
draw
explain the role of anaeorbic phototrophic oxidation in S compounds of global S cycling
H2S is converted to SO via anaeobic respiation
SO converted to H2S via chemo/phototrophic sulifde oxidation
(anaerobic)
SO is converted to SO4 from chemo/phototrophic sulfur oxidation (anerobic)
Just for your FYI electron flow of what bacteria is covered
GSB and PNSB
What similarites and differences do GSB and PNSBs have
*similarites and differences in mechanisms
*similatirites same/similar pigments under aerobic or aneobric conditions
*differences because of different sulfur metabolisms and electron donors
Explain electron flow in GSB
*anaerobes they have cyclic and non cyclic
*noncyclic e- yields NADHPH and consumes e- donors
1. redundant Fd, ferredoxin highly electronegative
2. directly reduces NADP+ from downhill e- flow
3. influx of e- from donor and loss to NADPH
*cyclic e- flow generates PMF and ATP, then recycles the e- back to photosystem that absorbs more light energy
Explain the conditions and implications of electron flow in PNSB
Aneorobic conidtions
* grows phototrophically under anaerobic conditions
* noncyclic: reverse e- flow generating NADH, it consumes PMP
*cyclic: generates PMF and ATP, some of that PMF is used to drive reverse e- flow
Aerobic conditions
*grows chemohetetrophically
*catabolism yields NADH and some ATP
*e- flow happens via ETC to O2, the TEA, in aerobic respiation generated PMF => ATP synthesis
What is Rhodobacter sphaeroides
- PNSB
- has cytoplasmic membrane infoldings
- the unfolding create large membrane for light harvesting complexes
*in low light, many complexes needed to capture reduces photons that strike the microbe
Explain the mechanism of phototrophic e- flow in PNSB, anaerobic conditions
- e-s are transfered from e- donor to PS via cytochrome
- reduces the photosystem with low energy e-‘s,
- light energy absorbed by reduced PS causing e-s to be raised to higher energy levels
- the e’s fall along chain of e carriers
- e- ‘s can be cycled to generate PMF (cyclic e- flow) or be transferred to NAD+ (non-cyclic e- flow)
- e- ‘s ‘lost’ to reduce NAD+ and are replaced by ‘new’ e- ‘s that enter at various points of the chain from e- -donor molecules
- e- -donors (non-cyclic e- flow): H2 , organic compound
Explain the mechanism behind non cyclic e- flow in PNSB during anaerobic growth
- in phototorphic anaeobic conditions, e-s plass from e- donro to e acceptor which is NAD+ via the PSI and reverse e- flow
- reduction potential of UQ is not good enough to directly reduce NAD+, so it requires uphill or reverse e- flow which is less powerful than PS
The reverse e- flow is powered by PMF via chemiosmotic not direct photonic energy
1. Hs falling back into the cell are powered by and deplete PMF, and the H (that fell back_ push e’ up hill
Meaning, NADH formation depends on photons and PMF, the formation takes e-s out of the cycle (NON CYCLIC)
Here the e- donors are NADH or NADPH
What does non cyclic e- flow yield in PNSB under anaerobic conditions
non cyclic e- flow yield in NADH or NADHPH
