What is Nucleosome? What is the Structure of Nuleosome?
The nucleosome can be defined as the constantly repeating basic unit of eukaryotic chromatin. Nucleosomes resemble a bead-like structure. It consists of a core of eight histone molecules and a piece of DNA containing about 150 base pairs. Each nucleosome is separated from each other by a linker DNA sequence containing approximately 50 base pairs. The nucleosome structure helps bring DNA into its breakable form during interphase. Otherwise, the linear length of a chromosome would be greater than the diameter of the nucleus.
These DNA base pairs are neatly wrapped around histone protein cores located in the nucleosome. The arrangement of nucleosomes resembles beads on a string. These nucleosomes are folded over and over to form the chromosome that 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?
Nucleosomes can be defined as the building blocks responsible for structuring and packaging the DNA held within the chromosome. The idea of squeezing a long piece of DNA material, the size of an entire DNA garden, into a smaller nucleosome is fascinating to most scientists. Everyone knows that compared to the size of DNA, the size of the cell is quite small. In fact, the diameter of the cell is only one hundredth of a millimeter.
So how does a long piece of DNA fit into this tiny cell? What the cell does is rewind the stretch of DNA over and over. There are many different and complex ways to do this. These basic blocks of cell building can be called nucleosomes. These are blocks containing a core of histone proteins. DNA wraps itself around these histone proteins in the nucleosome so that the formation of the chromosome takes place one small step at a time. The structure of the nucleosome is like beads on a string. But instead of passing through the strands, DNA wraps around it.
Today, researchers have found that the structure of the nucleosome is as follows: Two histones each from H2A, H3, H2B and H4 are combined to form the histone octamer. This octamer will then bind and wrap around 1.7 turns of DNA consisting of about 146 base pairs. When another histone, known as H1, is added, about 20 base pairs of DNA will be properly wound. This means that the DNA will be wound in two complete turns. This leads to the formation of a structure called chromatosome. A total of 166 pairs does not seem very long, as a single chromosome consists of about 100 million DNA base pairs in total. Chromosomes therefore consist of thousands of nucleosomes that come together with the help of the DNA wrapped around them. The DNA used in the joining process is known as linker DNA. Each of the chromosomes contains a long chain of nucleosomes. Studying the nucleosome diagram will help students better understand the subject.
To find the total DNA base pair in the nucleosome, the scientists treated the chromatin with a special type of enzyme that can cut DNA. These enzymes are known as DNases. Micrococcal nuclease or MNase enzyme has a very special feature. It cuts DNA, which acts as a linker for the nucleosome, just before it begins the process of cutting the DNA wrapped around histone octamers.
By adjusting the shear amount appropriately after the enzyme has been applied, the reaction can be stopped before each linker DNA is cut. In this case, chromatin will have only some mononucleosomes as well as dinucleosomes and trinucleosomes and some others. When the DNA is separated and held on a gel, certain bands tend to appear on the construct. There is a very simple explanation for this phenomenon, and that is the fundamentally repetitive structure of chromatin.
Nucleosome and Its Functions
Everyone knows that the nucleosome is made up of histone proteins that DNA will wrap around. These nucleosomes are then folded over and over to form the chromosomes that provide genetic traits to humans. Thus, the main function of nucleosomes is to ensure that long stretches of DNA can fit properly inside the cell and form the basic unit of life that allows us to live and breathe as we do today. Nucleosomes can be defined as structures that help DNA bind with histone protein and form chromosomes.