FIGURE 1. Local differences in membrane curvature are hallmarks of cellular membranes.

Many of the fine details of high local membrane curvature can be seen from the diagram (a) and the sample electron micrographs: b, fenestrations in the Golgi (from C. Hopkins and J. Burden, Imperial College London); c, tubule on endosomes (from P. Luzio and N. Bright, University of Utah); and d, HIV-1 viral budding (from W. Sundquist and U. von Schwedler, University of Utah). All of these can be described as local areas of positive or negative curvature (areas of high positive membrane curvature in a cell highlighted in red). Although it is fascinating to wonder how different membrane morphologies are adapted to the functions of different organelles, we concentrate here on how dynamic changes in morphology are generated. MVB, multi-vesicular body; ER, endoplasmic reticulum.