Light and life: How biological species respond to UV-radiation?
Sunlight is essential to life on earth both as an energy source to fuel photosynthesis for chemical energy and as a biological signal to control circadian rhythm in the life cycle. However, the UV radiation in sunlight, especially after recent ozone depletion, is detrimental to biosphere by causing DNA damage and cell dysfunction. Here, we present our recent studies on two important biological systems: One is to reverse damaged DNA to prevent potential skin cancer and the other is to trigger signal transduction for UV protection. With femtosecond spectroscopy and molecular biology methods, we mapped out the entire functional evolution by following the dynamics from the beginning to the end including a series of elementary processes of ultrafast energy transfer, electron transfer and chemical bond breaking and making. These biological dynamics occur ultrafast on the picosecond time scales and are in synergy to maximize biological quantum efficiency. These results reveal the molecular mechanism and functional photocycle at the most fundamental level and provide the molecular basis for future biomedical applications.