Plenary Lecture Abstracts

Penary I

Differences in the Interactions of Biological and Colloidal Surfaces

Jacob Israelachvili, Department of Chemical Engineering, and Materials Department, University of California, Santa Barbara, California 93106, USA

Recent experimental measurements of the interactions and forces between biological surfaces and molecules show that both the short-range forces (which determine adhesion or binding) and the long-range ‘colloidal’ forces (which determine equilibrium spacings and colloidal stability) can be much more complex than expected from simple theories, such as the DLVO theory. Biological or bio-colloidal interactions differ from ‘normal’ colloidal interactions in many ways: (1) biological interactions can be highly ‘specific’; (2) interacting bio-colloidal surfaces are usually 'asymmetric': the two surfaces or interacting molecules are different; (3) biological interactions are often ‘competitive’: a number of different interactions often compete simultaneously, one of which predominates; (4) interactions at one place can have an effect somewhere else (spatial dependence), and (4) non-equilibrium and time effects often play a crucial role (temporal dependence). It is unlikely that a single, generic, interaction potential can be written that covers all possible situations.


 

Penary II

Physical Aspects of DNA Confinement in Viral Capsids

William M. Gelbart, Department of Chemistry & Biochemistry, University of California at Los Angeles, Los Angeles, CA 90095-1569.

Two crucial steps in the process of viral infection of bacteria correspond to: (1) injection of the viral DNA into the bacterial cell, with the protein capsid remaining outside; and (2) loading of the replicated DNA’s into self-assembled capsids prior to lysis of the cell membrane. Step (1) begins as a passive process, requiring only that the DNA be highly pressurized in the viral capsid. Conversely, (2) is an active process involving the hydrolysis of ATP and the action of a motor protein that loads the DNA into the capsid. In this talk I discuss analytical and computational theory approaches which treat the basic physics underlying these processes. Both injection and loading steps are governed by the same quantity, namely the free energy density –internal stress, or pressure - associated with a semiflexible, self-repelling, chain whose persistence length is comparable to the confinement scale (capsid diameter) and whose overall length is hundreds of times larger. This pressure includes important contributions from bending energy, entropy of confinement, and self-repulsion. I also discuss the force acting on the DNA at different points in the injection/loading process, and treat its connection to current single-molecule experiments on viral loading dynamics.


Plenary III

Colloid Science, One Particle at a Time

David A. Weitz, Department of Physics and Division of Engineering and Applied Science, Harvard University, Cambridge, MA 01238.

Recent advances in microscopy have allowed visualization and manipulation of individual colloidal particles with unprecedented precision. Such experiments provide new insight and understanding about the structure and dynamics of colloidal suspensions and the influence of individual particle interactions on the macroscopic properties of the suspension. This talk will review a limited selection of such measurements, and will attempt to critically evaluate these advances within the more general perspective of the behavior and properties of colloidal suspensions.