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A diploid human cell has 46 chromosomes. A haploid cell has DNA approximately 3.2 billion bases long. What is the molar concentration of DNA in the cell then? How would we calculate?

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closed as unclear what you're asking by canadianer, David, AliceD Nov 16 '17 at 8:14

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    $\begingroup$ Welcome to Biology.SE! Is it a homework question? $\endgroup$ – Remi.b Nov 9 '17 at 16:41
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    $\begingroup$ What do you mean by "molar concentration of DNA"? Do you "molar concentration of nucleotides" or "molar concentration of DNA strands" or "molar concentration of chromosomes"? $\endgroup$ – Remi.b Nov 9 '17 at 16:42
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    $\begingroup$ @Remi.b Probably bases or nucleotides, that's maybe why he mentioned the base numbers... $\endgroup$ – Unicorn13601 Nov 9 '17 at 17:52
  • $\begingroup$ This question seems devoid of practical relevance or any particular biological interest. Why do you ask? $\endgroup$ – David Nov 11 '17 at 19:28
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I will assume that be "molar concentration of DNA", you mean "molar concentration of nucleotides".

Cell size

Assuming a cell with a radius of 0.05 nm (nanometer). Assuming a perfect sphere, the volume of such sphere is $5.24\cdot 10^{-4} nm^3 = 5.24\cdot 10^{-11} L$.

Of course, cell volume varies a lot among different cell types. The final result will drastically depend upon the cell volume considered (Thanks to @Roland fo highlighting that in the comment).

Number of nucleotides

In the nucleus

The haploid genome size is about $3.2\cdot 10^9$ nucleotides. The whole genome is therefore $6.4\cdot 10^9$ nucleotides. As there are two DNA strands at each haploid genome, we have to further multiply by two to get $1.28\cdot 10^{10}$ nucleotides. Note that this number could be lower at other moment of the life cycle. What I am computing here is the maximal number of nucleotides per nucleus

In the mitochondria

There are about 1500 mitochondria per cell. Each mitochondria contains about 16,000 nucleotides resulting in a total of $2.4\cdot 10^7$ nucleotidesin mitochondria per cell.

mitochondria + nucleus

$2.4\cdot 10^7 + 1.28\cdot 10^{10} ≈ 1.28\cdot 10^{10}$. That is mtDNA is negligible.

In the mols

The Avogadro number is about $6 \cdot 10 ^{23}$. Hence, there are $\frac{1.28\cdot 10^{10}}{6\cdot 10^{23}} = 3.2\cdot 10^{-14}$ mols of nucleotides per cell.

Molarity

Molarity is defined is defined as the number of mols per liter. It is therefore

$$\frac{3.2\cdot 10^{-14}}{5.24\cdot 10^{-11}} ≈ 0.0006M$$

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  • $\begingroup$ Nice, but I would add that this depends heavily on the cell volume, which varies a lot between cell types. The cell volume you use (52.4 pL) would be a very large cell: typical mammalian cells range from 1--5 pL in my experience (in cell culture). For such cells, the concentration is an order of magnitude higher, around 5mM. (Of course, the DNA nucleotides are not free, so this "concentration" is artificial.) Also, the "0.05nm" must be a typo, since that would yield a sphere volume of 5.24E-28 L. $\endgroup$ – Roland Nov 11 '17 at 9:21
  • $\begingroup$ But the poster asked specifically about moles of DNA, not moles of nucleotide, mentioning the number of chromosomes. I think the question is pretty silly and best ignored, but if you are going to answer, I think you should do so properly. $\endgroup$ – David Nov 11 '17 at 19:34

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