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What is the cellular specific mass, in units of pgDW (pico-gram dry-weight) per pL (pico liter)?

I suspect there is some variability between cell types, but this variability must be limited. Perhaps bacteria and mammalian cells are different, but the number shouldn't change much among bacteria. This is just intuition, I could be wrong.

So, what is the cellular specific mass, for different cell types (assuming there is limited variability, so this is not an infinite table)?

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Density of a variety of cell types is rather well known. It can been measured directly by examining buoyancy (tendency to float) in liquids of known density, and also by microfluidic methods. But the results depend on the osmolality of the solution in which the cells are kept, since cells tend to "swell" (take up water) in low osmolality (hypotonic) medium.

Using a microfluidic technique, this paper reports a density of 1160 $\pm$ 1 pg/pL for E.coli at 290 mOsm, and 1139 $\pm$ 3 pg/pL for red blood cells. At comparable osmolality and using a gradient centrifugation method, this paper gives a density of 1095 pg/pL for E.Coli. So the results clearly differ a bit depending on experimental conditions (possibly the medium composition was different). For budding yeast, this paper estimates a density of 1103 $\pm$ 3 pg/pL, compared to 1113 pg/pL by gradient centrifugation.

In all cases, cells are heavier than pure water (1000 pg/pL), and larger eukaryotic cells seem to be slightly more dense. As macromolecules are more dense than water, this would suggest that eukaryotes have lower water content.

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The most common opinion about this is a bacterium weighs about 10^-12 g. Here is a link with different results found using different techniques: http://hypertextbook.com/facts/2003/LouisSiu.shtml

This link also has useful relevant numbers, good to keep alongside: http://kirschner.med.harvard.edu/files/bionumbers/fundamentalBioNumbersHandout.pdf

Assuming a bacterial cell has a volume of 1 um^3 (10^-18 m^3; 0.001 pL) and 1 pg in mass, the density should be around 10^3 pg/pL. Similarly you can find out for other cell types.

Cheers!

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  • $\begingroup$ Can you confirm that those are dry weights? $\endgroup$
    – a06e
    Mar 17, 2016 at 6:46
  • $\begingroup$ What becko means is that you should add a reference for each value that you mention. If you have taken them from BioNumbers then you can provide the BioNumbers ID or even better (and highly recommended) the actual reference (Pubmed IDs given in BioNumbers). $\endgroup$
    – WYSIWYG
    Mar 17, 2016 at 6:58
  • $\begingroup$ Also, a number for mammalian cells would be nice. $\endgroup$
    – a06e
    Mar 30, 2016 at 16:05
  • $\begingroup$ As per dry weights: E. Coli has an avg. dry weight of 0.28 * 10^-12 g. (BNID: 103904, link: book.bionumbers.org/…). So, multiply the result above by 0.28. For mammalian cells, total weight per cell varies but on an average it is 3-4 ng. (Pubmed ID from Bionumbers: 17389958; BNID: 108454). The cell vol. varies: 100-10^4 um^3.(rpgroup.caltech.edu/publications/SnapShot2010.pdf). There is no concrete literature about the ratio of dry weight to total weight, but it is thought to be around 50-70%. Again these are avg. estimates. $\endgroup$
    – Grb
    Mar 31, 2016 at 17:05
  • $\begingroup$ Thanks for pointing out the calculation mistake @Roland .Of course for an accurate analysis you may need direct density measurement data, and also in that sense you will only get an average density of the cell as cells are highly heterogeneous. What I mentioned along with the specific references are some of the evidences of what have been done so far. $\endgroup$
    – Grb
    Apr 18, 2016 at 1:23

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