Probing the Machinery of Life
by Tom C. Lubensky
There is emerging consensus among physicists and biologists that resolutions to many of the important problems in the life sciences will require a marriage of molecular biology and physics. Physicists are reductionists and tend to seek a few simple rules that govern a range of phenomena; biologists focus on the details of how the structure of a protein affects its function, for instance, or how a particular DNA sequence expresses itself through the production of molecules essential to life.
Tools developed by physicists have led to revolutions in biology: the electron microscope provided the first images of the cell's interior; the control of nuclear isotopes, nuclei with different masses but identical chemical properties, made it possible to mark individual molecules; X-ray scattering is still the primary tool for determining the structure of biological molecules.
New technologies developed by physicists are again opening windows on the submicron world, providing new tools for the study of biological problems. New types of optical microscopes coupled with digital imaging techniques provide heretofore unobtainable information. Laser tweezers, which can grab and manipulate micron-sized particles, allow for controlled measurements of molecular forces. Experiments with laser tweezers measure the forces required to stretch and twist an isolated DNA molecule. New lasers and light scattering techniques make new data about time-dependent phenomena available. The motion and rigidity of cells are controlled in part by a network of long, very rigid actin molecules. The elastic and flow properties of these networks are being measured by direct observation of marked actin molecules and by light scattering from micro-sized spheres embedded in the network.
Penn is a place where communication between biological and physical scientists is growing. The University is well positioned to be a major player in the emerging interdisciplinary study of biological processes.
Dr. Lubensky is the Mary Amanda Wood Professor of Physics.