A whole lot of gelatin

Over the summer I am thinking a bit about how proteins and other stuff move around inside our cells, and those of other living organisms. I am trying to do this quantitatively, and so I need numbers for various aspects of living cells and of organisms. So I was delighted to find that there is an entire searchable website just for numbers related to living organisms, called, sensibly enough, BioNumbers, plus a related book: Cell Biology by the Numbers, by Ron Milo and Rob Phillips. Both websites are a mine of useful information. For example, one entry is the total length of fibres of the protein collagen in our bodies. The total length is about 100 billion kilometres, or to put in another way, in each of our bodies there is enough collagen to go from the Earth to the Sun 10,000 times.

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There is a lot physicists don’t know about living cells, but we do know some things, such as you don’t have hot mitochondria

Mitochondria, mammalian lung - TEMLast year, Chrétien  et al. published a paper in PLOS Biology on mitochondria. Two mitochondria are shown above, they are structures inside our cells where a key part of our energy metabolism take place. I don’t want to be harsh, but the central claim of their work is clearly wrong. This claim is that the mitochondria inside cells are at a temperature of around 50 C, more than 10 C higher than the rest of the cell which is about 37 C. This really cannot be right, the mitochondria inside your body are at the same 37 C that the rest of you is, and with a little physics it is easy to see why.

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Being useful to molecular biologists really boosts your citations

cite_barplotIn an earlier blog post, I noted that by one metric for the impact of my published work I lose out to F.D.C. Willard, who was a cat. In a similar vein, above I have plotted the number of citations to my most highly cited paper of the last few years, Dynamic Stratification in Drying Films of Colloidal Mixtures by Fortini et al., together with the number of citations of a 1970 paper by Laemmli. In Laemmli’s paper, he pioneered a technique called SDS PAGE. Note that the column with our paper appears blank, this is because on the scale of the plot, the bar for our paper is less than one pixel high. At the bottom I have replotted this bar graph on a logscale, where you can see the number of citations of our work. Continue reading

Dissolving in a hurry

We have all added salt or sugar to water and seen it dissolve. Both salt and sugar dissolve rapidly, but exactly how fast do they dissolve? This is one of those seemingly innocent questions, that is a lot harder to answer than you might expect, or hope. For something highly soluble like salt we expect the sodium and chloride ions at the surface of the dissolving salt crystal, to very rapidly move into solution in the surrounding water. But  if the water is stationary, not stirred, then near the surface of the salt crystal, we quickly reach the point where the water is saturated with salt, and no more can dissolve, until the sodium and chloride ions move away.

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Is the Royal College of Music really ‘underperforming’?

female_grad_earnThe Department of Education and the Institute for Fiscal Studies have a report out on graduate earnings. The plot for average graduate earnings for women, 5 years after graduation is above (it is Figure 9 of the report, the plot for men is similar). Graduate earnings vary widely by course and by institution — the two are strongly correlated of course, the degrees the London School of Economics (LSE) offers are very different from those offered by the Royal College of Music (shown as ‘RC Music’ above).

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Membrane proteins and the Curse of Dimensionality


I am at a conference in Sorrento, Italy. My hotel room is described as having a ‘hill view’, and as you can see from this picture taken from my hotel room, the description is accurate. That is a genuine Italian hill. In Sorrento, I will be talking about my work on paint drying, but I have a bit of time before the conference sessions start. So, I am also working on a course I am teaching next month for the EU network on RAtionalising Membrane Protein crystallisation (RAMP).

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Rinsing the dirt away

Clothes washing Louvre G547Few things are more boring and take less thought than putting a load of washing in the washing machine, but there is a lot of physics and chemistry going on inside washing machines. The basic idea is remove stains and dirt particles from your clothes, and to then carry them away down the drain. To do this washing powders and pods contain surfactants (soaps) to help detach stains and dirt from clothes, but then these molecules and particles must be removed from the clothes, and washed away.

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