L20: Phototrophy and Sulfur

Question 1

What do photosystems do

Answer 1

absorbs photons and use it to energise e-s

Question 2

Describe energy levels for PS2 + 1

Answer 2

PS2: -0.4 redox potential => +1.2 ox potential (very oxidising, splits water)

PS1: -1.2 =>0.6

Question 3

Distinguish between short vs long wavelengths

Answer 3

short = more energy
Long = less energy

Question 4

What is PS2’s job, what is the equation

Answer 4

pulls e- from water and release O2
H2O(e-donor) = 2H+ + 2e + O2

the PS pigments are reduced as e- donors are oxidised HUH

Question 5

PS2 steps

Answer 5

1. ps2 harvest short, high-energy light
2. light energy transfered to e-, raised to higher energy levels making them highly electronegative
3. e- falls along e- carriers, given to PS1
4. the fall yields energy =>making H+ pumped across membranes thereby feuling H+ gradeint
5. this in turn fuels ATP synthesis and ATP fuels CO2 fixation

Question 6

PMF

Answer 6

proton motive force (H+)

Question 7

PS1

Answer 7

1. e- passed here then PS1 absorbs more light energy
2. 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

Question 8

Describe cyclic vs non cyclic electron flow (oxygenic)

Answer 8

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

Question 9

Explore Anozygenic Microbial photosynthesis, what does this reveal

Answer 9

• 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

Question 10

What are the conditions of anoxygenic electron flow

Answer 10

• 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

Question 11

What is the end product of anoxygenic electron flow

Answer 11

yields ATP

Question 12

Explain the mechanism behind cyclic e- flow in anoxygenic phototrophs

Answer 12

*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

Question 13

Explain noncylic e- flow in anoxygenic phototrophs

Answer 13

*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]

Question 14

Contrast the key different between S and NS bacteria

Answer 14

non sulfure bacteria tend to be more sensitive to H2S
S can accumilate So

Question 15

Draw the sulfur cycle

Answer 15

draw

Question 16

explain the role of anaeorbic phototrophic oxidation in S compounds of global S cycling

Answer 16

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)

Question 17

Just for your FYI electron flow of what bacteria is covered

Answer 17

GSB and PNSB

Question 18

What similarites and differences do GSB and PNSBs have

Answer 18

*similarites and differences in mechanisms
*similatirites same/similar pigments under aerobic or aneobric conditions

*differences because of different sulfur metabolisms and electron donors

Question 19

Explain electron flow in GSB

Answer 19

*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

Question 20

Explain the conditions and implications of electron flow in PNSB

Answer 20

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

Question 21

What is Rhodobacter sphaeroides

Answer 21

• 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

Question 22

Explain the mechanism of phototrophic e- flow in PNSB, anaerobic conditions

Answer 22

1. e-s are transfered from e- donor to PS via cytochrome
2. reduces the photosystem with low energy e-‘s,
3. light energy absorbed by reduced PS causing e-s to be raised to higher energy levels
4. the e’s fall along chain of e carriers
5. e- ‘s can be cycled to generate PMF (cyclic e- flow) or be transferred to NAD+ (non-cyclic e- flow)
6. 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
7. e- -donors (non-cyclic e- flow): H2 , organic compound

Question 23

Explain the mechanism behind non cyclic e- flow in PNSB during anaerobic growth

Answer 23

1. in phototorphic anaeobic conditions, e-s plass from e- donro to e acceptor which is NAD+ via the PSI and reverse e- flow
2. 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

Question 24

What does non cyclic e- flow yield in PNSB under anaerobic conditions

Answer 24

non cyclic e- flow yield in NADH or NADHPH

Question 25

Describe cyclic e- flow in PNSB

Answer 25

• PMF is generated as e- fall along the e- TC and back into photosystem via cyclic e- flow
  *protons are pumped out as e- fall along the chain, generating PMF
  *PMF used to drive ATP biosynthesis, flagellar rotation, reverse e- flow

Question 26

Distinguish between reverse and forward e- flow

Answer 26

Forward:
oxidises NADH (strong e- donor), e- loose their energy with each step, yielding ATP
reduces TEA

Reverse:
oxidses external weak e- donor, e-s gain energy with each step, consumes PMF and yields NADH

Question 27

Explain non cyclic electron flow in PNSB during aeorbic conditions

Answer 27

1. they are chemoheterotrophs
2. oxidsing organic/inorganic compounds for energy/electrongs
3. e- pass to terminal oxidase via aeorbic respiration
4. NADH is produces by catabolic reactions, serves as e- donor for biosynthetic/respiratory PMF processes