From bacteria to algae to eggs, all cells have some degree of asymmetry — or polarization — in their structure and function. Functional polarization relies on specific macromolecules being sorted to particular sites in the cell, and the challenge is to work out how cells sort and locally retain macromolecules. Perhaps nowhere is this so difficult as in the case of proteins in the cell membrane, because their ability to diffuse in the plane of the membrane should defy the cell's attempts to position them. Some cells (such as epithelia) have obvious physical barriers to free diffusion of membrane components. But although nature's most polarized cells, neurons, lack such barriers, certain proteins are clearly restricted to specific regions of the plasma membrane. How can this be?
展开▼
