GENERAL MICROBIOLOGY - T.P. Pyrog - 2004

18. PHOTOTROPHIC BACTERIA AND PHOTOSYNTHESIS

18.3. PHOTOSYNTHESIS PROCESSES

Conclusions

1. Under the action of light, Electron transfer from a donor to an acceptor proceeds in a thermodynamically unfavorable direction (from a positive redox potential to a negative one).

2. The photosystem is replenished with electrons via external Donors (oxygen-evolving Photosynthesis uses Water; anoxygenic photosynthesis uses sulfide, elemental sulfur, molecular hydrogen, or Organic compounds).

3. Electrons are supplied through cyclic and non-cyclic pathways. In cyclic transport, electrons return from the reduced acceptor to the oxidized donor. In oxygenic photosynthesis via non-cyclic transport, electrons for the second photoreaction originate from water, while those for the first originate from the Electron Transport Chain connecting both Photosystems. In non-cyclic transport (anoxygenic photosynthesis), electrons can be derived from sulfide, elemental sulfur, molecular hydrogen, or organic compounds.

4. Both cyclic and non-Cyclic electron transport are accompanied by directional proton translocation, A change in membrane charge, and the generation of a transmembrane electrochemical proton gradient. Protons are transported across the membrane from the outside in. The transfer of a single electron is accompanied by the influx of two protons into the inner space.

The photosynthetic apparatus Functions as a light-driven proton pump.

5. During photosynthesis, the energy of the proton-motive force is converted into ATP energy through mechanisms identical to those operating in the prokaryotic Cell/33.html">Plasma Membrane or eukaryotic Mitochondria.

6. Non-cyclic electron transport leads (along with altering the membrane charge) to the reduction of NAD(P)H.

7. In oxygenic photosynthesis (cyanobacteria, green plants), where water serves as the hydrogen donor, the functioning of two photoreactions is required. This process results in ATP synthesis, NADP reduction, and the release of molecular oxygen (electrons for the second photoreaction are liberated during The oxidation of water to oxygen).

8. In anoxygenic photosynthesis, a single photoreaction operates because hydrogen and electron donors with a more negative redox potential than water are utilized.

In purple Bacteria, photosynthesis exclusively yields ATP. NAD reduction does not occur (as non-cyclic Electron transport is absent in this case, given that the Redox Potential of the electron acceptor is -0.1 V). NADH is formed via Reverse Electron Transport.

In green bacteria, photosynthesis produces both ATP and NADH (since the redox potential of the electron acceptor is -0.5 V).

9. Photosynthesis is the most prevalent chemical reaction on our planet. We owe both the continuous Production of organic matter and the existence of fossil fuels such as coal, petroleum, and natural gas to photosynthesis.