Question

3. i) Given that the human genome is 3.2 billion base pairs, calculate the length of DNA in a typical human diploid somatic cell. Assume B-form DNA.

ii) Calculate the number of nucleosomes needed to wrap the DNA in a human cell into chromosomes. Assume 200bp DNA per nucleosome.

iii) From this number, calculate the number of histone protein molecules needed to wrap the DNA in a human cell into chromosomes.

Answer 1

i) Total no. of base pairs = 3.2 billion base pairs = 3.2x 109

We know that distance between two base pairs is 0.34nm

so for a DNA having 3.2 billion base pair the length of DNA would be = 1.088 x 109 nm = 1.088 m

ii) Given, 200bp per nuclesome

for a human cell chromosome the total no. of bp = 3.2x 109

so, no. of nucleosome = 3.2x 109/ 200 = 1.6 x 107

iii) No. of histone protein in every nucleosome = 8

So, total o. of histone proteins = 8 x 1.6 x 107  = 12.8 x 107