How Many Nucleosomes are Present in a Human Cell

Introduction

There are about 30 million nucleosomes in a human cell. Nucleosomes are a part of Deoxyribonucleic acid (DNA) present in the human body for the transfer of genetic information from parents to offspring.

Nucleosomes and their structure

Nucleosomes are subunits of chromatin, about 11nm in diameter and 5.76nm in height. Eight cores of histone molecules are present around nucleosomes and these histone molecules are bounded by 2 circles of DNA strands around it. Histone is a protein and the eight-core histone is called histone octamer, each histone octamer is made up of two same histone proteins H2A, H2B, H3, and H4. Typically, nucleosomes have around 200 base pairs of DNA. Nucleosomes are wrapped in eukaryotes.

The structure of nucleosomes was first discovered by Aaron Klug’s group in the 1980s. They showed that histone octamer (protein) wraps DNA around itself in about 1.7 turns of a left-handed superhelix. Richmond group in 1997 showed the first crystal structure of nucleosome describing every small detail about it. Today, we have solved the structure of over 20 different nucleosome core particles including those containing histone and its variants from different species.

Discovery of nucleosome

Don and Ada Olins first discovered nucleosomes in 1974 and Roger Kornberg showed their structure and proven existence. It was found as a regulator of transcription by Lorch et al in 1987 in Vitro, in 1987 by Han and Grunstein and by Clark Adams et al in 1988.

Define Human cells.

Cells are the basic building block of the human body and all other living beings. Trillions of cells are present in the human body. They perform the different functions by energy which they get from the food we eat, they take the nutrients from the food for energy. Our human body is developed and formed of cells.

Define Histones.

Histones are proteins containing a large amount of Lysine and Arginine residues which are present in eukaryotic cell nuclei. They are having alkaline in nature. Histones are surrounded with DNA to form a unit called nucleosomes. They play a very important role in gene transcription and can be modified using enzymes.

Define Chromatin.

Chromatin is composed of DNA and proteins found in eukaryotic cells (i.e., histone). Chromatin helps in packaging long DNA molecules into a more compact and denser structure, which helps prevent tangles in DNA strands. It also helps in preventing further cell division, and cell damage and regulating gene expression and DNA replication.

How to calculate nucleosomes in a human cell?

The number of nucleosomes in a human cell can be calculated as:

The DNA in a human cell = 6.6 × 109 base pair (bp)

We know that,

1 nucleosome = 200 bp

Therefore, 1bp = 1/200 nucleosomes

Hence, 6.6 × 109 bp will have = (1 × 6.6 × 109)/ 200 nucleosomes i.e., 3.3 × 107 nucleosomes = 33 × 106 nucleosomes = 33 million nucleosomes.

\begin{array}{l}

6.6 \times\ 10^9 \text {bp}=\left(1 \times\ 6.6 \times\ 10^9\right) / 200 \\

3.3 \times \ 10^7 \\

=33 \times \ 10^6 \\

=33 \text { millions }

\end{array}

Conclusion

Nucleosomes are a vital part of a human cell, as they carry epigenetically inherited information in the form of covalent modification of their core histones. On calculating the number of nucleosomes in each human cell is 33 million. It may fluctuate in some cases so, approximately 30 million nucleosomes are present in a human cell.