Biophysics of contractility

Abstract

Mechanical work is performed by all living organisms. Moving of cells or cell aggregates (organs like muscles or organisms as a whole) is the most obvious form of mechanical work; it gives organisms the ability to move away from a noxious environment or to move toward beneficient regions of space. However, movements inside the cells are also forms of mechanical work performed by most if not all living cells. These include processes like transport of particles and organelles in different directions within the cell, protoplasmic streaming, mitosis (cell division), swelling and contraction of organelles, and endocytosis. Common factors prevail in all these cases; first, the energy source is always the free energy of the hydrolysis of ATP to ADP and inorganic phosphate. Furthermore, most mechanisms share a common underlying molecular basis. Wherever cell movement is studied on the molecular level, it turns out to involve one particular class of proteins of which actin and myosin are the best known. These proteins, or combinations of them, generally exhibit ATPase activity, which clearly indicates their importance in the transduction of chemical energy into mechanical work.