Question

How many such beads (nucleosomes) do you imagine are present in a mammalian cell?

Answer 1

Nucleosome

1. A nucleosome consists of DNA which is wrapped around a protein core (histone octamer).
2. The DNA that wraps around the histone octamer is called core DNA and part of the DNA that connects two nucleosomes is called linker DNA.
3. Nucleosome serves as a packaging unit for the DNA.
   

Representation of a nucleosome

Calculation of the number of nucleosomes in a mammalian cell

1. A typical nucleosome contains 200 bp of DNA helix.
2. Total base pairs in mammalian diploid cells = 6 x109 bp

The number of nucleosomes present in the mammalian cell can be calculated by:

Number of nucleosomes = Total number of base pairs /Number of base pairs per nucleosome

= 6 x 109/200 =3 x 107nucleosomes

Approximately 30 million nucleosomes must be present in a mammalian cell, the exact number is difficult to find.