1. Photosynthetic organisms
Anoxygenic Photosynthesis
Green and purple (sulfur and non-sulfur) bacteria and heliobacteria
Oxygenic Photosynthesis
Cyanobacteria

2. 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

3. Pigment
Chl a
Chl b
BChl a
BChl b
BChl c
BChl d
BChl e
Color in graph above
black
red
magenta
orange
cyan
blue
green
Absorption maxima (nm)
430, 663
463, 648
364, 770
373, 795
434,666
427,655
469, 654
Other pigments can harvest light energy at wavelengths an organism’s chlorophyll cannot – includes caratenoids, phycobilins (blue), and phycoerythrin (red)

5. 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
for animation...

6. Anoxygenic photosynthesis

7. 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.

8. 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)

9. 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