Question

If you assume the average length of DNA wrapped in the nucleosome is 146 bp and the average length of linker DNA is 50 bp, approx how many nucleosomes are found in the haploid humane genome, which contains 3 billion bp?
Based on the information for nucleosome structure above, how many molecules of histone H2A would you calculate are in a DNA sequence that is 46,000 bp in length?

Answer 1

1. The DNA packaged in to chromosomes is associated with histones. DNA and histones together make up the nucleosome. The nucleosome consists of both the core DNA and the linker DNA that are associated with histones. The DNA that is wrapped in the nucleosome is the core DNA. The core DNA is wrapped around a histone octamer of H2A, H2B, H3 and H4. The linker DNA links the histone such as H1 and H5 to the nucleosome.

Given are the following:

Average length of DNA wrapped in a nucleosome=146 bp

Average length of linker DNA= 50 bp

Total DNA in haploid humane genome= 3,000,000,000 bp

Nucleosome= Core DNA + linker DNA= 146bp + 50 bp= 196 bp

Hence, nucleosome has 196 bp of DNA.

Number of nucleosomes in a 3 bp haploid humane genome= Total DNA in haploid human genome/DNA associated with one nucleosome

Number of nucleosome in haploid humane genome= 3,000,000,000 bp/196 bp= 15306122.45

Rounding the figure to number without decimal places, gives number of nucleosomes in haploid humane genome to be 15306123.

2. DNA content in core histones= 146 bp

Linker region DNA = 50 bp

Nucleosome= 146+50= 196 bp

Total DNA sequence= 46000 bp

Number of nucleosome in total DNA sequence= 46000/196= 234.69= 235

There are two molecules of H2A in each nucleosome.

Number of H2A in total DNA sequence= 235 X 2= 470 molecules