The human genome contains about 31 109 bp of DNA Assuming t

The human genome contains about 3.1 × 109 bp of DNA. Assuming that the DNA is covered with nucleosomes spaced as described in this chapter, how many molecules of histone H2A are present in one somatic human cell? (Do not consider any reductions in H2A due to its replacement by H2A variants.) How would the number change after DNA replication but before cell division?

Solution

Nucleosome is the integrative structure of Negatively charged DNA and Positively charged Histone proteins. Each nucleosome contain 200 base pairs of DNA and one H1, two H2A, two H2B, two H3 and two H4. Histone octamer formed from two H2A, two H2B, two H3 and two H4 and it wraped with nearly 200 bp DNA. So every 200 bp, two H2A histones present. If the size of haploid Human genome is 3.1 × 10⁹ bp, then diploid somatic cell DNA size is 6.2 × 10⁹ bp. Total H2A histones in Diploid somatic cell are: 6.2 x 10⁹ / 200

= 3.1 x 10⁷

After DNA replication the H2A number become bouble = 6.2 X 10⁷