Femtobiology.

Functions of biologically active molecules are frequently initiated by elementary chemical reactions such as energy and electron transfer, cis-trans isomerizations, and proton transfer. The nature of these reactions generally makes them very fast and efficient, occurring on picosecond and femtosecond timescales. Ultrafast spectroscopy has played an important role in the study of a number of biological processes and has provided unique information about several of nature's responses to light. Here I review the current understanding of light-energy collection and conversion in photosynthesis, the function of carotenoid molecules in photosynthesis, and the primary light-initiated reactions of the photoreceptors rhodopsin, bacteriorhodopsin, photoactive yellow protein, phytochrome, and a new type of blue-light receptor based on flavin chromophores.