Membranes by the Numbers

  • Rob PhillipsEmail author


Many of the most important processes in cells take place on and across membranes. With the rise of an impressive array of powerful quantitative methods for characterizing these membranes, it is an opportune time to reflect on the structure and function of membranes from the point of view of biological numeracy. To that end, in this chapter, I review the quantitative parameters that characterize the mechanical, electrical, and transport properties of membranes and carry out a number of corresponding order-of-magnitude estimates that help us understand the values of those parameters.


Membrane properties Fermi problems Biological numeracy Membrane shape 



One of the best parts of being a member of the scientific enterprise is all the smart and interesting people we get to interact with. In preparing this chapter I sent out a survey to many experts in membrane biology and biophysics and was overwhelmed with the thoughtful responses that I received from many colleagues. I am grateful to Olaf Andersen, Patricia Bassereau, Joel Dacks, Markus Deserno, Evan Evans, Ben Freund, Jay Groves, Christoph Haselwandter, Liz Haswell, KC Huang, Ron Kaback, Heun Jin Lee, Mike Lynch, Bill Klug, Jane Kondev, Ron Milo, Uri Moran, John Nagle, Phil Nelson, Bert Poolman, Tom Powers, Doug Rees, James Saenz, Pierre Sens, Victor Sourjik, Stephanie Tristram-Nagle, and Tristan Ursell for useful discussions. I am especially grateful to Olaf Andersen, Markus Deserno, Christoph Haselwandter, James Saenz, Pierre Sens, and Tristan Ursell who have been patient and persistent in advancing my membrane education, though obviously all shortcomings in this chapter are due to my failure to absorb that education and are no fault of their own. I am privileged to be entrusted by the National Science Foundation, the National Institutes of Health, The California Institute of Technology and La Fondation Pierre Gilles de Gennes with the funds that make the kind of work described here possible. Specifically I am grateful to the NIH for support through award numbers DP1 OD000217 (Director’s Pioneer Award), R01 GM085286, and 1R35 GM118043-01 (MIRA). I am also grateful to the Kavli Institute for Theoretical Physics where much of this chapter was written. More generally, this article is part of an adventure that I have undertaken with Ron Milo and Nigel Orme (our illustrator) and generously funded by the Donna and Benjamin Rosen Bioengineering Center at Caltech. Finally and sadly, since the completion of this chapter, my friend and collaborator Bill Klug was brutally murdered in his office by a former graduate student. I had asked Bill to join me in the writing of this chapter, but he was too busy during this summer and instead of having the happy presence of his name as a co-author I instead have the solemn and unhappy duty to dedicate this short piece to him, kind and intellectually deep, above all a family man, he will be deeply missed.


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Authors and Affiliations

  1. 1.Department of Applied Physics and Division of Biology and Biological EngineeringCalifornia Institute of TechnologyPasadenaUSA

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