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Balancing benefits and damage - life with oxygenic photosynthesis

Photosynthesis is the only biochemical process on Earth which can convert light into chemical energy. All our food, oxygen that we breathe, and almost all the energy that we consume comes from this process which is performed by plants and cyanobacteria. The origins and evolution of photosynthesis are explained by several theories which predict that the process was assembled from biochemical and electron transfer pathways which have evolved separately in different organisms. Fossil evidence of the early photosynthesis cannot be found, but isotopic measurements suggest that the process existed shortly after life has evolved, some 3.7 billion years ago. Earliest forms of photosynthesis were anoxygenic, with oxygenic forms arising significantly later. Invention of the ability to use water as an electron donor producing O2 as a waste product which accumulated in the atmosphere entirely changed the life on Earth some 2.4 billon years ago. Complex forms of life which utilize O2 during aerobic respiration could develop. Simultaneously, reduced carbon products had to be buried into the Earth’s crust by geological processes, thus enabling further accumulation of O2 in the atmosphere. However, O2 can serve as an efficient electron acceptor in many biochemical energy transfer reactions, which results in formation of highly reactive and damaging reactive oxygen species (ROS). Which mechanisms of access energy dissipation and ROS scavenging oxygenic phototrophs had to develop to enable sustained carbon fixation? How are energy-conserving and -dissipating pathways prioritized in photosynthetic membranes of vascular plants?

cyanobacteria; endosymbiosis; energy-conserving pathways; energy-dissipating pathways

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