Polymer science and biology: structure and dynamics at multiple scales
Original Entry by Holly McIlwee, AP225 Fall 09
Polymer science and biology: structure and dynamics at multiple scales (Opening Lecture) L. Mahadevan, Faraday Discussions, 139, 9, 2008.
Studying biological systems at a molecular and cellular level can help probe two types of questions: What are the underlying processes affecting life on a larger scale?, and How can we translate what is going on at the cellular level in biological systems to polymer systems? In this review Mahadevan chose to focus on two elements of biological structures: filaments and membranes. Filamentous aggregates and their affinity to form ordered bundles, which move relative to one another passively and actively, or disordered aggregates, which display behavior not seen in individual filaments, are studied at a fundamental level in order to relate their function to life on a supramolecular scale. Simple cell dynamics are also examined to probe questions relating to the microstructure of the cytoplasm, cell attachment to a substrate or other species, and the cell's ability to spread disease. The intent is to learn more about a highly complex system by looking simply at it, and to start to think about conclusions that can be drawn and ultimately how this can relate to polymeric systems.
Cells have heterogeneous structures made up of solid and liquid phases containing structural filaments, proteins, the cytoskeleton, and microtubules as well as water, ions, and soluble proteins. Cells are particularly interesting to study because they are autonomous, replicating, repairing, traveling, communicating with their environment, and evolving on their own. The cell is an example of a structured fluid.
The microstructure of the cytoplasm is of particular interest to the author. Because of the porpous membrane the cell experiences dilatational movement when a load is applied to the membrane. When the load is applied the structural network dilates and experiences unequilibrium. As the fluid leaves the cell the load is bore by more of the gel and it can then relax and regain equilibrium. What is interesting to study is the rate at which equilibrium is reached. It is ultimately related to the poroelasticity of the system, the viscosity or the fluid crossing the membrane, and the size of its pores. Because of the size of the system and different membranes in the cytoplasm and the cell unequilibrium may cause blebbing in the cell which is usually brought on by a stimuli such as polarization. It is vital that there is a relationship betwen the membrance flow in the cytoplasm and the entire cell.
In order for tissues and organisms to form cell adhesion to other cells and to specific substrates must occur. This involves physical, chemical, and mechanical processes. Neglecting all of this and also the differences between different types of cells, the author chose to focus on how a cell responds to adhesion. It is determined that cell contact with a surface is related to the formation of interactions and bonds formed with the new surface. There exists a dynamic balance between the contact area, density of bonds, and the energy, and the strain on the shell or membrane. All in all though it has been found that regardless of cell type, the contact area grows linearly with time.
In conclusion it is seen that there are obviously paralelles amoung polymer science and these studies of biology, particularly when studying the limit to life's evolution, packaging of macromolecular assemblies, and disease mechanisms and ultimately prevention strategies. As the author states in this field the "challenges are as great as the opportunities".