Chapter

Photosynthesis

Volume 34 of the series Advances in Photosynthesis and Respiration pp 3-32

Date:

The Photosynthetic World

  • Martin F. Hohmann-MarriottAffiliated withDepartment of Biochemistry, University of Otago
  • , Robert E. BlankenshipAffiliated withDepartments of Biology and Chemistry, Washington University Email author 

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Summary

Photosynthesis, the conversion of sunlight into energy that is available to sustain cellular metabolism, is accomplished by a diverse group of organisms. The present photosynthetic diversity has been shaped over billions of years through the interactions of the genetic makeup and metabolic capabilities of each organism with its environment. Some photosynthetic bacteria found today can live in anaerobic conditions as must have been the case with the first photosynthetic organisms found on the primordial Earth. The oxygen of our present atmosphere was generated by ancient cyanobacteria. Cyanobacteria were incorporated into non-photosynthetic organisms in a process called endosymbiosis, giving rise to all the photosynthetic eukaryotes. Competition for light led to the development of a multitude of pigments that together span the entire solar spectrum. These pigments are arranged in special light-harvesting antenna systems that have evolved to efficiently channel excited-state energy to the reaction centers. In reaction centers, electrons are stripped away from donor molecules. This charge separation event, and successive electron transfer reactions, are catalyzed by multisubunit membrane-embedded protein complexes that are connected together via mobile electron carriers. The electron transfer reactions are ultimately used to convert inorganic carbon into organic carbon compounds. Most ecosystems rely on consuming photosynthesis-derived organic molecules and photosynthesis-derived oxygen to sustain life.