Membranes by the Numbers

Abstract

The Quantitative Membrane LandscapeThe pace at which biology is advancing is staggering. Just as there was a short 50 year gap between the invention of manned flight by the Wright Brothers and the beginning of the space age, in the little more than a half century since the discovery of the structure of DNA and its interpretation through the genetic code, the life sciences have entered their own age, sometimes dubbed "the genome age". But there is more to living matter than genomes. While the genome age has unfolded, a second biological revolution has taken place more quietly. This other success story in the emergence of modern biology is the unprecedented and detailed microscopic view of cellular structures that has been garnered as a result of the emergence of new ways to visualize cells. Both electron and optical microscopy have afforded an incredible view of the cellular interior. In addition, the use of techniques for profiling the molecular contents of cells has provided a detailed, quantitative view of the proteomes and lipidomes of both cells and the viruses that infect them meaning that, in broad brush strokes, we know both what molecular components the cell is made of and how the cellular interior looks. A particularly fertile example that serves as the backdrop for the present chapter is given by our ever improving understanding of the membrane organization associated with the organelles and plasma membranes of cells of many kinds. [1] The goal of this chapter is to develop a feeling for membranes in the form of biological numeracy. That is, for the many different ways we can think about membranes whether structurally, mechanically or electrically, we will try to formulate those insights in quantitative terms. The strategy used here is to move back and forth between a data-based presentation in which key quantitative facts about membranes are examined, and a rule-of-thumb and simple-estimate mentality, in which we attempt to reason out why those numbers take the values they do. For those cases in which we introduce hard data, our device will be to use the so-called BioNumbers ID (BNID).[2] Some readers will already be familiar with the PMID (Pubmed ID) that links the vast biological literature and databases. Similarly, the BioNumbers database provides a curated source of key numbers from across biology. By simply typing the relevant BNID into your favorite search engine, you will be directed to the BioNumbers website where both the value of the parameter in question will be reported as well as a detailed description from the primary literature of how that value was obtained. Unfortunately, my presentation is representative rather than encyclopedic. There is much more that could have (and should have) been said about the fascinating question of membrane numeracy. Nevertheless, the hope is that this gentle introduction will inspire readers to undertake a more scholarly investigation of those topics they find especially interesting, while still providing enough quantitative insights to develop intuition ab...

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