Physical Properties of Living Cells

The cell is the unit of life and the properties of single cells are the basis of their aggregate behavior and of the physiology of living organisms. Among the properties of single cells, we will review the physical properties, including the volume, density, mass, and the electrical properties. While these physical quantities are the most basic of the physical properties of matter, they reflect and affect the underlying complex biological activities in a cell. Physicists and biologists have been asking how biological mechanisms control the cell’s physical properties and how physical properties regulate biological processes. For example, the single parameter of transmembrane electrical potential is regulated by a cohort of proteins (ion channels and ion pumps); conversely, the activity of these proteins is controlled by the transmembrane potential. Measuring the physical parameters of a single living cell is difficult because of the small size and fragility of the cell and the aquatic environment required to keep the cell alive. We will review technological advances in the measurement and the control of the physical properties of cells and will illustrate the biological significance of a physical understanding of living cells with examples from the authors’ research.