Question

What is the composition difference between chromosomes,chromatin and nucleosome?

Answer 1

DNA in the nucleus does not exist in free linear strand form. It is associated with proteins called histones and condensed into a structure called chromatin. Hence, chromatin can be defined as the highly condensed form of DNA with histone proteins. Under the microscope, chromatin appears as a string made up of beads as shown in figure 01. One bead is known as nucleosome, and it is the basic structural unit of chromatin. Chromatin forms the chromosomes of eukaryotic organisms and is packaged inside the nucleus. The structure of chromatin is visible only during the cell division under the microscope.

There are two forms of chromatin namely euchromatin and heterochromatin. Euchromatin is the less condensed form of chromatin which can be transcribed into RNA during the expression. Heterochromatin is the highly condensed form of chromatin which is not normally transcribed into RNA. Highly condensed supercoiled DNA in the form of chromatin is best suited to pack inside the nucleus which has a small volume.

The main function of chromatin is to pack DNA efficiently inside the nucleus which has a very small volume. Chromatins also perform additional functions such as protecting DNA structure and sequence, allowing mitosis and meiosis, preventing chromosomal breakages, regulating gene expression, and DNA replication.

Nucleosome is a small section of chromatin which is wrapped around the core histone protein. It looks like a bead in a string. Core histone protein is an octamer composed of eight histone proteins. Two copies from each histone protein are in the core octamer. The histone protein composition in the core octamer is H2A, H2B, H3 and H4. Core DNA tightly wraps around the globular core histone octamer and makes a nucleosome. Nucleosomes are then arranged into a chain like structure and wrapped around additional histone proteins tightly to make the chromatin in the chromosomes.

The length of the core DNA strand which wraps around the histone octamer in the nucleosome is approximately 146 base pairs. The approximate diameter of the nucleosome is 11 nm, and the spiral of nucleosomes in the chromatin (solenoid) has a diameter of 30 nm. Nucleosomes are supported by additional histone proteins to package into tightly coiled structure inside the nucleolus.
Composition
Chromatin is composed of DNA and histone proteins. Nucleosome is composed of 147 base pair length DNA and eight histone proteins.
In the nucleus of each cell, the DNA molecule is packaged into thread-like structures called chromosomes. Each chromosome is made up of DNA tightly coiled many times around proteins called histones that support its structure

Answer 2

Chromosomes are located on the chromatin fibres where as chromatin is located inside nucleus.chromatin is a coiled string like structure where as chromosomes are rod like structures . chromatin is made up of DANA and proteins and chromosomes will transfer the heritable characters to their daughter cells