The Department of Physics at the Faculty of Science, in collaboration to the Physics Department at the Junior College, is organising a talk for staff and students. The talk will be delivered by Prof. em. Dr Urbaan M. Titulaer (Institute for Theoretical Physics at Johannes Kepler University in Linz, Austria).
The talk, entitled 'Looking at Single Biomolecules: How Physics can help in understanding life', will be held on Wednesday 15 March at 14:30 in Room 401 Maths and Physics Building (MP401).
Prof. em. Dr Urbaan M. Titulaer will discuss a few methods used at the Johannes Kepler University to study processes in cells. The first one uses fluorescent ligands attached to specific biomolecules. A laser that excites the fluorescent groups is then directed at the cell and the fluorescent photons are detected, e.g., by a CCD camera. The individual photons show a Gaussian distribution of a size comparable to the wavelength of the light, but by measuring the full distribution, the centre of the Gaussian, and hence the location of the biomolecule, can be determined about an order of magnitude more precisely than by regular optical methods.
The second method, which Prof. Titulaer will discuss in somewhat more detail, uses an atomic force microscope (ATM), in which a tip of atomic dimensions is used to scan a surface, in this case a cell membrane. When one attaches an antibody to the tip, the atomic force microscope can be used to locate corresponding antigens in the membrane: the ATM acts as a nanoscopic angling rod. The forces between antigen and antibody can then be studied by measuring the force needed to break the antibody away from the antigen. Since the experiment is carried out at room temperature and in a watery environment, the force actually needed varies between repetitions of the experiment, and a distribution of breakup forces is measured. This distribution also varies when the speed of retraction is varied: when one retracts slowly, smaller applied forces are needed, since one can take better advantage of spontaneously occurring fluctuations. He will sketch a simple model of the antigen-antibody bond that explains the measurements, and can be used to determine some of the relevant physical parameters.
The Theoretical Biophysics group investigates molecular light harvesting systems in plants and blue-green algae. Models are constructed that use structural information (usually obtained at conditions different from those occurring in a living cell) and fluorescence spectra from living cells to explain the structure in the living cell and its relation to biological function. The models can also be used to design artificial light harvesting complexes.
