Why is a chromosome important?
All genes are joined together to form the DNA. This DNA is condensed to form the nucleosome and present together in the form of the chromosome. All the genes are ultimately present on the Chromosome. These genes are responsible for the formation of protein and enzymes.
These chromosomes have all the genetic information and are transferred to the next generation through the process of sexual reproduction.
Walter Flemming discovered the first chromosome in 1882. Before this discovery, the chromosome was considered the X factor. After discovering the chromosome, Henking discovered the sex chromosome and named it the X chromosome in grasshopper.
How Chromatin packed into DNA
The length of the DNA is approximately 2m which is very large and cannot fit into the cell without coiling. All the genes are present in the chromosome. These chromatin materials have to be condensed, and for condensation, the histone protein comes into action.
These histone proteins are basic in nature, while DNA is acidic in nature, due to which they form a complex structure known as a nucleosome. The eight nucleosomes join together to form the histone octamers, which have the DNA in condensed form.
These octamers are present in a long thread known as chromomere, which has around 200-300 octamers and is packed inside the nucleus. There are two types of packing: Euchromatin and heterochromatin.
What is chromatic fibre?
In the human body, there are 46 chromosomes, out of which 44 chromosomes are autosomes, and two chromosomes are sex chromosomes. These chromosomes help form the protein and the enzyme essential for the body’s growth and development.
The DNA is present in a coiled structure inside the nucleus. These chromatin materials are duplicated by the process of replication in the S phase of the interphase.
After the replication, the Chromatin material and DNA transfer their information into the RNA by a process called transcription. In the process, one strand of the DNA is copied into the RNA.
The RNA is read by the ribosome and helps in the formation of the required protein by a process called translation. Any abnormality during the transcription and the translation will lead to mutation and abnormal character.
There is a modification process in the RNA that helps avoid mutation.
Structure of the Chromatin
The structure of the chromosome can be best studied at metaphase. The primary constriction of the chromosome represents the position of the centromere.The centromere is covered by the kinetochore plate. The kinetochore plate is made up of tubulin protein and spindle protein.
The kinetochore plate acts as the site for attachment of the spindle. Secondary constriction on the chromosome makes the position of the nuclear satellite region (NOR). A chromosome having a satellite is called sat chromosome, whereas the sat chromosome acts as a marker.
In humans, these chromosomes act as markers:-
- Chromosome 1
- Chromosome 1
- Chromosome 15
- Chromosome 21
- Chromosome 22
The chromosome having DNA is called chromonema and chromonemata, while the beaded appearance in the chromosome is called chromomere.4
The composition of the chromatin material is as follows: –
- DNA
- Histone protein
- Non-histone protein
- RNA
- Ions
- Enzyme
- Matrix
Types Of Chromosome
There are different types of chromosomes depending on the centromere and they are: –
1- Metacentric: – A chromosome whose centromere is located at the centre is called the metacentric. Due to this, the chromosome arm will divide into two equal arms and the X shape.
2- Sub-metacentric: – A chromosome whose centromere is located just near the centre is called a sub-metacentric. Due to this the chromosome arm will divide into two unequal arms and a V shape. In humans, several chromosomes are submetacentric: chromosome 6, chromosome 4, chromosome 4, chromosome 2,
3- Acrocentric: – A chromosome whose centromere is located just near the terminal is called acrocentric. Due to this, the chromosome arm will divide into two unequal arms and an L shape.
In humans, chromosome 15, chromosome 14, chromosome 15, chromosome 21, chromosome 13, and Y chromosome are acrocentric.
4- Telocentric:- A chromosome whose centromere is at the terminal is called telocentric. Due to this, the lower arms of the chromosome are not visible and have only two arms.
Functions of Chromatin
Functions of Chromatin in Mitosis
Prophase: During the prophase of mitosis, Chromatin fibres are not seen properly and present in a loosening form.
Metaphase: During metaphase, the chromosome is highly condensed and can be easily visible.
Anaphase: During anaphase, the sister chromatid starts separating from each other for division.
Telophase: In telophase, Chromatin material reaches the end of the pole and from the two cells having the same DNA content.
Packaging of DNA: Compactification of long DNA strands is the most important function of chromatin. The size of the compartment in which DNA is housed in the nucleus is significantly greater than the length of DNA in the nucleus. The DNA must be compressed in some way to fit into this compartment.
The packing ratio is a measurement of how tightly DNA is packed. DNA is not packaged directly into the structure of chromatin to achieve the total packing ratio. Instead, it has numerous organisational structures.
Regulation of Transcription : Transcription is the process by which proteins read the genetic information stored in DNA and then transcribe it into RNA, which is then translated into functional proteins. There will be no transcription if the chromatin is reinforced and access to the read proteins is restricted. The transcription process can be carried out by euchromatin, an expanded kind of chromatin. While heterochromatin, a condensed form of chromatin, is too densely packed for proteins to read DNA.
Conclusion
Therefore, chromatin plays an important role in the various processes occurring in the body. The formation of the protein, enzymes and hormones are regulated by the chromosomes. This chromatin material is only responsible for transferring the genes from the parents to the offspring.