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# How many atoms are in a cell?

Ed Rybicki ed at MOLBIOL.UCT.AC.ZA
Thu Sep 18 03:19:02 EST 1997

```> From:          webmaster at cbmpan.gdynia.pl
> Subject:       Re: How many atoms are in a cell?

> >Irina Gayevskaya wrote:
> >> I was wondering, how many ATOMS are there in the simplest unicellular

> More like 10^14
> Assuming the cell being just a tiny drop of water (after all its mostly that):
> cell volume in the range of 10^-9 ml
> water MW=18g/mol
> you get:
> the number of moles of water in the cell: 10^-9/18 moles/cell
> the number of water molecules in the cell: (10^-9x6x10^23)/18 molecules/cell=
> (10^14)/3 molecules/cell
> and as each water molecule has 3 atoms:
> the number of atoms per cell: 3x(10^14)/3=10^14 atoms/cell

Funny, I get a different value...

From:                 Self <MOLBIOL/ED>
To:               irinag at erols.com

> I was wondering, how many ATOMS are there in the simplest
> unicellular organism (excluding bacteria - those that have nucleus)?

OK...well, they're going to be mainly water anyway, so if you
calculate a volume of 0.5 x 0.5 x 0.5 micron (=0.125 x 10 exp -18
cubic metres) with a density of 10 exp 3 kg/cubic metre...MW water is
18, Avogadro's number is 6.0225 x 10 exp 23, so 1.25 x 10 exp -16 kg
is 4.2 x 10 exp 9 molecules, x3 for atoms = 13 000 000 000!!

And again: 0.5 micron = 0.5 x 10^-4 cm, volume cell = 12.5 x 10^-14
cm^3, mass (as density=1) = 12.5 x 10^-14 g, no. moles water =
10^23) = 4 x 10^9 molecules,

= 12 x 10^9 atoms.

This is, of course, assuming SMALL cells (0.5 micron is small for a
eukaryote) - but if you assume 10 micron cells for a SIMPLE
eukaryote, this means 8 000 x more atoms - or 10^14, almost spot
on....!
Ed Rybicki, PhD
Dept Microbiology     |   ed at molbiol.uct.ac.za
University of Cape Town  | rybicki at uctvms.uct.ac.za
Private Bag, Rondebosch  |  phone: x27-21-650-3265
7700, South Africa    |   fax: x27-21-689 7573
WWW URL: http://www.uct.ac.za/microbiology/ed.html

"Every year is getting shorter, never seem to find the time..."

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