Courses for Kids
Free study material
Offline Centres
Store Icon


share icon
share icon

What is a Nucleosome and its Structure?

MVSAT 2024

A nucleosome can be defined as the basic unit of eukaryotic chromatin that keeps on repeating. In the cells of human beings, a total of about 6 feet of the DNA has to be packed into the nucleus that has a diameter that is less than a single strand of human hair. There are about 150 different base pairs of DNA sequences present in one nucleosome. 

                                                         (Image will be uploaded soon)

These DNA base pairs are wrapped properly around the histone protein cores which are present in the nucleosome. The arrangement of the nucleosomes resembles that of beads that are arranged on a string. These nucleosomes are repeatedly folded in order to create the chromosome which provides us with genetic characteristics. In this article, students will learn about DNA packaging nucleosomes and chromatin 310 along with some other details about nucleosomes. 

What is Nucleosome?

The nucleosomes can be defined as the building blocks which are responsible for the structuring and packing of the DNA that is held within the chromosome. The entire idea of fitting a lengthy stretch of DNA material that resembles the size of an entire DNA yard into a smaller nucleosome is pretty fascinating to most scientists. Everyone knows that the size of the cell is pretty small when compared to the size of the DNA. In fact, the cell has a hundredth of a millimetre of diameter. 

So, how does the long stretch of DNA fit into the smaller cell? Well, what the cell does is it coils the DNA stretch again and again. There are so many different and complex ways to do that. These fundamental blocks of cell-building can be called nucleosomes. These are the blocks that contain a core of histone proteins. The DNA wraps itself around these histone proteins in the nucleosome and hence the formation of the chromosome happens one small step at a time. The structure of the nucleosome resembles that of beads being put into the string. However, the DNA wraps around the strings instead of going through them. 

(Image will be uploaded soon)


In the present times, the researchers have figured out the structure of nucleosome to be as follows: Two histones each from H2A, H3, H2B, and H4 are grouped together in order to create the histone octamer. This octamer will then bind and wrap about 1.7 turns of the DNA which consists of about 146 base pairs. With the addition of another histone known as H1, about 20 base pairs of the DNA will be wrapped properly. This means that the DNA will be wrapped in two full rounds. This leads to the creation of the structure which is called chromatosome. The 166 pairs in total don’t seem much long since a single chromosome consists of about 100 million DNA base pairs in total. Therefore, the chromosomes are made up of thousands of nucleosomes which are combined together with the help of the DNA coiling around them. The DNA that is used in the process of joining is known as linker DNA. Every single one of the chromosomes contains a lengthy chain of nucleosomes. Studying the diagram of nucleosome will help students understand the topic in a better way. 

In order to find out the total base pairs of DNA in the nucleosome, scientists treated chromatin with a particular type of enzyme that can cut the DNA. These enzymes are known as DNases. The enzyme micrococcal nuclease or MNase has a very special property. It cuts the DNA which acts as a linker for the nucleosome right before it begins the process of cutting the DNA wrapped around the histone octamers. 

With the proper regulation of the cutting amount after applying the enzyme, the reaction can be stopped before every single linker DNA is cut. In this case, the chromatin will just have some mononucleosomes as well as dinucleosomes and trinucleosomes along with some others. In case the DNA is separated and kept on a gel, certain bands tend to appear on the structure. There is a very simple explanation for this incident and that is the fundamentally repeating structure of chromatin. 

Nucleosome and its Functions

Everyone knows that nucleosome consists of the histone proteins around which the DNA will wrap itself around. These nucleosomes are then repeatedly folded in order to create the chromosomes that provide genetic characteristics to human beings. So, the main function of the nucleosomes is to ensure that the long stretches of the DNA are able to fit properly inside the cell and create the basic unit of life that allows us to live and breathe as we are today. 


Nucleosomes can be defined as structures that help the DNA in binding with the histone protein and creating the chromosomes. From this article mentioned above, students will be able to know about DNA packaging nucleosomes and chromatin 310. 

Want to read offline? download full PDF here
Download full PDF
Is this page helpful?

FAQs on Nucleosome

1. What is nucleosome?

The definition of a nucleosome can be given as the basic unit of the eukaryotic chromatin that tends to keep on repeating. There are long stretches of DNA present in human beings and it has to be packed into smaller compartments that are known as cells. In total there are about 150 pairs of DNA which are also known as base pairs, that are kept inside one nucleosome. The nucleosome contains the histone protein around which the DNA will wrap itself. These nucleosomes are then repeatedly folded in order to create the chromosome. The chromosomes provide people with the genetic characteristics that they have after birth. 

2. What is the function of nucleosome?

The nucleosomes have a very important function and that is to ensure that the DNA which is quite lengthy on its own is able to wrap itself inside the cell, which has a comparatively smaller size. According to the nucleosome model Nucleosomes are made up of histone proteins around which the DNA will properly wrap itself. The histone octamer created with the pairing of two histones is the central agent in which the DNA wraps itself. After the creation of the nucleosome is complete, these nucleosomes are grouped together and folded repeatedly in order to create the chromosomes that tend to provide genetic characteristics to human beings.

Competitive Exams after 12th Science