Let’s know about Heterochromatin vs Euchromatin. The main difference between heterochromatin and euchromatin is that heterochromatin is the part of chromosomes that is strongly packed form and is genetically inactive whereas euchromatin is an unpacked (loosely) packed form of chromatin and is genetically active .
When the non-dividing cells of the nucleus were observed under the light microscope, it exhibited two regions depending on the concentration or intensity of the staining. Dark stained areas are called heterochromatin and lightly stained areas are called euchromatin.
Euchromatin is approximately 90% of the total human genome . They are parts of chromatin and participate in the conservation of DNA in the genome present inside the nucleus. In the year 1928, Emil Heitz coined the terms heterochromatin and euchromatin.
By concentrating on a few more points, we will be able to understand the difference between both the types of chromatin. Below is a brief description of them along with a comparison chart.
definition of heterochromatin
The region of chromosomes that is intensely stained with DNA-specific strains and is relatively condensed is known as heterochaetin . They are tightly packed forms of DNA in the nucleus .
The organization of heterochromatin is highly compact in such a way that it is inaccessible to proteins that are engaged in gene expression. Even chromosome crossing is not possible due to the above reason. As well as being consequential, they must be genetically inactive. There are two types of heterochromatin: constitutive heterochromatin and constitutive heterochromatin. Genes that are silenced through the process of histone methylation or siRNA via RNAi are called facultative heterochromatin . Therefore they are inactive genes and are not a permanent feature of every nucleus of the cells.
Whereas repetitive and structurally functional genes like telomeres or centromeres are called constitutive heterochromatin . These are the constant nature of the nucleus of the cell and there are no genes in the genome. This structure is maintainable during the interphase of the cell.
The main function of heterochromatin is to protect DNA from endonuclease damage; This is due to its compact nature. It prevents DNA regions from accessing proteins during gene expression.
definition of euchromatin
The part of chromosome which is rich in gene concentration and loosely packed of chromatin is called euchromatin . They are active during transcription.
Euchromatin comprises the majority of the dynamic genome in the interior of the nucleus and euchromatin is said to comprise approximately 90% of the entire human genome .
To allow transcription, parts of the genome containing active genes are loosely packed. The covering of DNA is so loose that DNA is easily accessible. The structure of euchromatin resembles that of the nucleosome, which consists of histone proteins, with about 147 base pairs of DNA wrapped around it.
Euchromatin actively participates in the transcription from DNA to RNA. The gene regulation mechanism is the process of converting euchromatin to heterochromatin or vice versa.
Activated genes present in euchromatin are transcribed to form mRNA, which in turn leads to functional proteins being the main function of the encoplatin . They are therefore considered to be genetically and transcriptionally active. The housekeeping gene is one of the forms of euchromatin.
Key Difference Between Heterochromatin and Euchromatin
Following are the important points to differentiate between heterochromatin and euchromatin:
- The tightly packed form of DNA in a chromosome is called heterochromatin , while the loosely packed form of DNA in a chromosome is called euchromatin .
- In heterochromatin, DNA has a higher density and is darker in colour , whereas euchromatin has a lower DNA density and is lightly stained .
- Heterochromatin is found only at the periphery of the nucleus in eukaryotic cells , and euchromatin is located in the inner body of the nucleus of prokaryotic as well as in eukaryotic cells.
- Heterochromatin shows little or no transcriptional activity as well as they are genetically inactive , on the other hand, euchromatin actively participates in the process of transcription and is also genetically active .
- Heterochromatin is compactly coiled and late replicating , whereas euchromatin is loosely coiled and early replicative .
- Regions of heterochromatin are viscous, but regions of euchromatin are non-sticky.
- In the heterochromatin part, the phenotype remains unchanged of an organism, although variation can be observed in euchromatin due to effects in DNA during the genetic process.
- Heterochromatin allows regulation of gene expression and also maintains structural integrity of the cell although euchromatin contains genetic variations , and allows genetic transcription.
From the above information regarding chromatin – their structure and types. We can say that only euchromatin is strictly involved in the transcription process, although heterochromatin and its variants do not play such an important role.
Constitutive heterochromatin contains satellite DNA, and it surrounds the centromere, and the facultative heterochromatin is dissolved. So clearly it can be said that eukaryotic cells and their internal structure are relatively complex.