Wednesday, September 21, 2011

Imagine that

In my last post I mentioned that there is an arm's length of DNA in (almost) every cell of our bodies. Several people expressed incredulity.

An arm's length of anything in a space too small to see with the naked eye! As I said in Skeptics and True Believers, it strained my credulity too. So I did the calculation. I didn't include the calculation in the book, but I once posted it here.

Here goes again.

We know from X-ray diffraction studies that a strand of DNA is 1.5 nanometers (1.5 x 10 to the -9 meters) in radius. Assume a cylinder 1 meter long (the arm's length) with a radius of 1.5 nanometers and work out the volume (length x pi r-squared). A typical animal cell is about 8 micrometers (8 x 10 to the -6 meters) in radius. Assume a spherical cell and calculate the volume (4/3 pi r-cubed). Do it yourself. You will see that the DNA fits easily inside the cell, with plenty of room for all of the rest of the cellular machinery.

The human imagination is hobbled by the limitations of the senses. Mathematics allows the imagination to go where the senses have not strayed.