A painting of the biconcave morphology of red blood cell. Image from Andrew Mason’s photostream

Still at the Physical Chemistry Summer School in Hefei. Continued with last post about Prof. Yang’s physical approach toward biological issues, the membrane budding phenomena catch the interest of physics.

Membrane budding is the fundamental process of many cell behaviors including endo- and exocytosis, cell division and intracellular secretion. As a good real-world example, the Golgi apparatus of eukaryotic cells has enjoy high and prolonged concern from biologists. However, most of them tend to consider the membrane budding process in a biological sense (an account on this). Prof. Yang introduced some theoretical approaches towards this phenomena.

Cell membrane belongs to a larger class of self-assembled molecular bilayer. As analogue, budding of self-assenbled polymer membrane may be indicative. Ilan Tsafrir et al. (Phys. Rev. Lett. 2001, 86, 1138-1141. DOI: 10.1103/PhysRevLett.86.1138) investigated the pearling of tube like polymer membrane induced by adding additional polymer in to the solution, and found that very small amount of added polymer may cause drastic change in curvature of the membrane. A model was built to predict polymer segregation according to local membrane curvature at late stages. This implies that adsorption of polymer (or other substance maybe) onto the membrane surface may affect the curvature and eventualy cause a budding. Tobias Baumgart and co-workers (Nature 2003, 425, 821-824. DOI: 10.1038/nature02013) comfirmed this in their experiment with lipid-dopped giant unilamellar vesicles. Membrane containing two different types of lipid (‘hard’ and ‘soft’) phase separates at different condition and show a large variety of ordered patterns, with the curvature also changing (a movie is available here). With the help of physical model, again, these shapes were related with some mathematical solutions of an equation.

Up till now, all physical approaches toward the abovementioned biological issues – assembly of TMV, polyhedron shapes of virus, and budding of cell membrane – do not involve anything about gene. This is not a coincidence. Prof. Yang is very confident that physics, rather than genetics, governs the process biological dynamics. Physicists should pay more attention to biological issues and, most importantly, biologists should attach more importance to data collecting, besides ‘fantasy’ of mechanisms, so that physicists can have enough experimental data to check and improve their theories.

Prof. Yang will continue to study the biconcave shape of red blood cell, pigment distribution on colorful animal, and other biological issues, via a non-genetic, physical route.