Klaus Schulten.
From simplicity to complexity and back: Function, architecture and
mechanism of light harvesting systems in photosynthetic bacteria.
In H. Frauenfelder, J. Deisenhofer, and P. G. Wolynes, editors,
Simplicity and Complexity in Proteins and Nucleic Acids, pp. 227-253,
Berlin, 1999. Dahlem University Press.
(pdf available from author upon request).
SCHU99
Photosynthetic organisms fuel their metabolism with light energy and have developed for this purpose an efficient apparatus for harvesting sunlight, key features of which had been conceptually established long ago. Recently, the atomic structure of a main protein constituent of the apparatus, as it evolved in purple bacteria, has been solved through a combination of modeling, x-ray crystallography and electron microscopy. This permitted the modeling of the entire light harvesting system, a complex nanometric aggregate of transmembrane proteins. We discuss in this chapter how a still ongoing analysis wrestled from an atomic level structure an explanation of the light harvesting function based on quantum physics. The investigations of the light harvesting system of purple bacteria demonstrate particularly clearly the voyage typical for research in biological physics that starts from a simply stated, known function and proceeds through experimental and theoretical investigations carried out at more and more refined levels of molecular reality: first the macromolecular components of the underlying system are identified and their role characterized, e.g., through spectroscopy; then the complex structures of these components are established at atomic resolution and functionally relevant architectural elements are recognized; finally, through refined observation and theoretical analyses of these elements the physical mechanisms exploited by the organism to achieve the cellular function are determined.
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