Self Assessment Answer # 10
for Lesson 19

by Dr Jamie Love © 2002 - 2005
Genetics Course

This is really a math question meant to get you to think about the length of DNA. It helps if you have a comfortable understanding of logarithms - or a good calculator and careful fingers.

Here is how to imagine the equation.

Three billion (3 x 109) base pairs are each separated by 3.4 angstroms (3.4 x 10-10 meter).

Your answer is "base pairs divided by length per pair" which is

3 x 109 base pairs / 3.4 x 10-10 meter per base pair = 3 / 3.4 x 101 meter = 0.88 meter

So your haploid genome, from one cell, would about 88 centimeters tall (the height of an average desk).

By the way (I didn't ask you but), how many helical turns would there be in a haploid human genome?
You know there are ten bases per complete turn (because each base is rotated by 36 degrees with respect to the previous one) so simply divide ten into three billon to discover that there are 300 million turns in the helix of a haploid human genome.
(In point of fact, the helix is broken into 23 chromosomes and there is a great deal of distortion of the helixes in the chromosomes for packing - but you get the general idea.)

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