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Photosynthetic organisms. Anoxygenic Photosynthesis Green and purple (sulfur and non-sulfur) bacteria and heliobacteria. Oxygenic Photosynthesis Cyanobacteria. Pigments. Light harvesting pigments Bacteriochlorophyll (bchl) for anoxygenic photosynthesis

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photosynthetic organisms
Photosynthetic organisms
  • Anoxygenic Photosynthesis
    • Green and purple (sulfur and non-sulfur) bacteria and heliobacteria
  • Oxygenic Photosynthesis
    • Cyanobacteria
pigments
Pigments
  • Light harvesting pigments
    • Bacteriochlorophyll (bchl) for anoxygenic photosynthesis
    • Chlorophyll for oxygenic photosynthesis
    • Different varieties that can absorb light at different wavelengths

Harness energy from light to excite electrons to higher energy states (more reducing, more negative E0) – these high energy electrons go through the electron transport chains to ultimately produce energetic molecules like ATP and NADPH to drive biochemical reactions in the cell

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Other pigments can harvest light energy at wavelengths an organism’s chlorophyll cannot – includes caratenoids, phycobilins (blue), and phycoerythrin (red)

q cycle
Q cycle
  • Ubiquinone (Q) pool is critical to H+ shuttling to maintain the pmf and drive phosphorylation to produce ATP

Quinone (Q) is reduced with an electron through cytochrome bc1 to form hydroquinone (QH2) – QH2 is then oxidized by another site on cytochrome bc1 back to Q – this shuttles H+ across the membrane, the H+ goes through ATPase back into the cell, generating ATP

http://www.geocities.com/awjmuller/anims_images/bacterialPSfast.gif for animation...

anoxygenic photosynthetic organisms
Anoxygenic photosynthetic organisms
  • Purple and green bacteria utilize bchl and H2S, S8, S2O32-, H2, Fe2+, and organics as electron donor
    • Many can deposit elemental sulfur intracellularly (and sometime outside the cell (epicellularly) to store that when H2S is unavailable
    • The term non-sulfur does not necessarily mean they can’t use sulfur - they are generally adapted to environments with less sulfur
  • Heliobacteria – Nitrogen-fixing, heterotrophic organisms found in soils and rice paddies

Beggiatoa spp.

oxygenic photosynthesis
Oxygenic Photosynthesis

Chlorphyll a (P680) is very oxidized (E0=+1.1V), enough to oxidize H2O. BUT e- excitation takes it to E0=-0.7V, not enough to reduce NADP+ to NADPH. Thus a need for 2 photosystems….

Water-oxidizing complex is key – Mn4Ca-complex that oxidizes H2O to O2 in 4 steps (S0 through S4)

non cyclic phosphorylation
Non-cyclic phosphorylation
  • Coupled photosystems linked by plastocyanin (pc), which takes the e- excited by P680, after it goes through the Q pool, and puts it into a similar chlorophyll a (P700) which is excited by a photon to a very reduced potential (-1.3V) that can reduce NADP+ to NADPH
  • If there is enough NADPH, PS I can act independently and function for cyclic phosphorylation