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Nucleosome model


Nucleosome is called the unit of DNA packaging.

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This is how we can understand why DNA packaging is necessary in the cell.

In total, more than 6 billion Nitrogenous Bases are found in the diploid content of Human.

If we want to measure the length of DNA present in only human cells in meters, then it is around 2.2 meters.

In total, more than 6 billion Nitrogenous Bases are found in the diploid content of Human.

On the other hand, talk about the nucleus, whose total dimension is only 10-6 meters.

So how does such a long piece of DNA (about 2.2 meters) fit into such a small nucleus?

In today’s post, we will try to understand about this.

DNA packaging in Eukaryotes

Due to the nucleosome, a very long DNA is packaged and shortened and fit into a correct size in a eukaryotic or prokaryotic cell.

However, at both sites, different basic proteins participate in the packaging of DNA.

We all know that DNA is acidic in nature, so it needs basic proteins to pack it.

So that the condition of the medium becomes neutral in the entire nucleus or cytoplasm.

Histone proteins

Histone proteins are used as basic proteins in eukaryotic cells.

The basic nature of histones is due to the abundance of two types of amino acids. The names of these two basic amino acids are Arginine and lysine.

Histone proteins are made up of five types of subunits.

The core part of the histone protein is found in the form of an 8 subunit octamer, which means that the histone octamers protein has eight subunits.

The names of these sub-units are as follows-

H1, H2A, H2B, H3, and H4 (H1, H2A, H2B, H3 and H4).

Out of these two polypeptide chains of H2A, H2B, H3, H4 are found. The histone octamer forms the core of the nucleosome around which the DNA is wrapped.

A total of 200 base pairs of DNA is wrapped around the histone core.

The DNA used to join two nucleosome is called linker DNA.

The H1 protein acts as a plugging protein in the nucleosome.

This type of DNA packaging system is found in eukaryotic cells, be it protists or multicellular and complex organisms, such as humans.

Everywhere the nucleosome model serves as the basic unit in DNA packaging.

The nucleosome further coils even more compactly to form a solenoid.

If we look at the nucleosome with an electron microscope, it appears like a necklace of pearls, for which the term beads on a string is also used.

Higher level packaging of DNA requires some additional basic proteins.

These proteins are called non histone proteins.

DNA packaging in prokaryotes cell

How would DNA packaging happen in a prokaryotic cell?

Prokaryotic cells use non-histone basic proteins called polyamines for DNA packaging.

Here we have to note one more thing that, nucleus is not found in Prokaryotic cell.

Therefore, in Prokaryotic cell, DNA is present only in the cytoplasm.

DNA in prokaryotic cell is called nucleoid.


In today’s post, we understood the following questions related to nucleosomes such as-

What is the nucleosome model?

Histone is a protein?

However, any kind of suggestion or update and if you see any mistake, then you must tell us.

We will try our best to update your suggestion or any mistake which happened somewhere in the post.

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