Physics Colloquium, Tuesday, 3 December 2002

Biophysics - Photosynthesis

Neal Woodbury

Arizona State University

Photosynthesis is the process by which solar energy is converted into a biochemically useful form: membrane potentials, high energy bonds, reductive potential, etc. The photosynthetic machinery that performs the light absorption and initial energy transduction involves an antenna system designed to have a large cross section for light absorption and a reaction center – a complex that uses excited states to drive a transmembrane electron transfer reaction. The structural details of this biological opto-electronic system are now known to atomic resolution and with the help of ultrafast laser spectroscopy, the energy and electron transfer reactions involved in the energy transduction process have been worked out in some detail. Recent work in our lab has concentrated on how the protein environment of the reaction center determines the direction and nature of the photochemical reactions. We are now able to switch the electron transfer reaction between two symmetrically related electron transfer chains in the reaction center, either through mutagenesis or by changing wavelength and pH. This is a biological model for a molecular scale electronic switch.

As the photosynthesis research has progressed, we have come to realize that it is also possible to use light, and particularly ultrafast laser pulses, to both probe and manipulate single molecules or spatially resolved groups of molecules and cells. This in turn has allowed us to begin to develop methods for using light to control rapid screening and selection of living cells, which we are applying to directed evolution of molecules, as well as to attach complex patterns of molecules to surfaces in spatially defined ways. We have also been able to use ultrafast lasers to perform single molecule analysis of fluorescence lifetimes and anisotropies, providing a window into the detailed mechanisms of biological systems on the single molecule level.

3.30 p.m., Smith Laboratory, Room 1005

Refreshments served in Smith 1094 at 3:00 p.m.