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