Heterochromatin Vs Euchromatin Over view
When stained with nuclear stains, heterochromatin, which contains sequences that are not active during transcription, exhibits strong stains.
- It comes in up to four or five different forms, each of which is identified by different combinations of epigenetic markers.
- Heteropycnosis, which is the differential staining of chromosomal sections, may occur from the staining of heterochromatin.
- The genes on this chromosome are often inactive and not expressed, which distinguishes them from euchromatin.
- The periphery of the nucleus contains heterochromatin. Additionally, prokaryotic cells do not have it, indicating that this type evolved later.
- However, constitutive heterochromatin and facultative heterochromatin are the two types that are most frequently seen.
- In all cells of the same species, constitutive heterochromatin typically stores the same DNA sequences. It may be found in structural forms like centromeres and telomeres and is often repeated.
- The genes present close to the densely packed chromosomes may be impacted by the genes in constitutive heterochromatin.
- Genes 1, 9, 16, and the Y chromosome in males have higher concentrations of this heterochromatin.
- Genes that are often silenced by a variety of methods are packaged by facultative heterochromatin. However, unlike constitutive heterochromatin, facultative chromatin packages diverse genes in various animals within the same species.
- Despite not being repeated, the facultative chromosome shares the same structural elements as constitutive heterochromatin.
- The process of morphogenesis or differentiation controls the production of facultative heterochromatin.
- In humans, one of the two X chromosomes found in females is expressed as euchromatin, while the other is inactivated as facultative heterochromatin.
- Heterochromatin serves a variety of purposes. Some of these include maintaining chromosomal integrity and gene control.
- The closely packed DNA in heterochromatin protects the chromosomes from numerous protein factors that might cause DNA binding or improper chromosomal destruction by endonucleases.
- Additionally, heterochromatin permits epigenetic marker inheritance and gene control.
With less strong staining and DNA sequences that are transcriptionally active or may become so at some point during growth, euchromatin is a more loosely packed form of DNA.
- About 90% of an organism’s genome is made up of euchromatin, which is located in the nucleus’ core.
- After staining, it shows as light-colored bands under an optical microscope.
- Heteropycnosis is prevented by the homogeneous staining of all euchromatin components.
- However, it appears as an elongated 10 nm microfibril under an electron microscope.
- Euchromatin’s structure may be seen as a thread of beads that has been unfurled, with the beads representing nucleosomes. Histone proteins found in the nucleosomes cover a certain amount of DNA.
- Since the histone proteins’ covering of the euchromatin is loose, the individual DNA sequences may be exposed.
- A region of the chromosome known as the histone tail is thought to regulate the conformation of euchromatin.
- The bacterial genome’s single confirmation of chromosomes, euchromatin, raises the possibility that it developed before heterochromatin.
- In contrast to heterochromatin, euchromatin does not have two forms. Only constitutive euchromatin is present.
- Given that it includes genes that are transcribed into RNA and ultimately into proteins, euchromatin is very significant.
- Because the DNA in euchromatin has an unfolded form, regulatory proteins and RNA polymerase may attach to the sequences and start the transcription process.
- When they are not to be transcribed and are no longer active, certain genes in the euchromatin may be transformed into heterochromatin.
- Gene expression and replication are controlled by the conversion of euchromatin to heterochromatin.
- Some genes, such as housekeeping genes, are constantly organised in the euchromatin conformation for this function since they must be continuously copied and translated.
Key Differences (Heterochromatin vs Euchromatin)
|Basis for Comparison||Heterochromatin||Euchromatin|
|Definition||Heterochromatin is a tightly packed or condensed DNA that is characterized by intense stains when stained with nuclear stains and transcriptionally inactive sequences.||Euchromatin is a more lightly packed DNA that is characterized by less intense staining and DNA sequences that are transcriptionally active or might become transcriptionally-active at some point during growth.|
|Staining||Heterochromatin is darkly stained under nuclear stains.||Euchromatin is lightly stained under nuclear stains.|
|DNA conformation||In heterochromatin, the DNA is tightly bound or condensed.||In euchromatin, the DNA is lightly bound or compressed.|
|The DNA in heterochromatin is folded with the histone proteins.||The DNA in euchromatin is unfolded to form a beaded structure.|
|Genes||The genes present in heterochromatin are usually inactive.||The genes present in euchromatin are either already active or will be active during growth.|
|Transcription||Heterochromatin is transcriptionally-inactive.||Euchromatin is transcriptionally-active.|
|DNA content||Heterochromatin has more amount of DNA tightly compressed with the histone proteins.||Euchromatin has less amount of DNA lightly compressed with the histone proteins.|
|Content in genome||Heterochromatin forms a smaller part of the genome. In humans, it makes about 8-10% of the genome.||Euchromatin forms a more significant part of the genome. In humans, it makes about 90-92% of the genome.|
|Found in||Heterochromatin is found only in eukaryotes.||Euchromatin is found in both prokaryotes and eukaryotes.|
|Types||Heterochromatin exists in two forms; constitutive and facultative heterochromatin.||Euchromatin exists in a single form; constitutive euchromatin.|
|Location within the nucleus||Heterochromatin is present towards the periphery of the nucleus.||Euchromatin is present in the inner body of the nucleus.|
|Heteropycnosis||Heterochromatin exhibits heteropycnosis.||Euchromatin doesn’t exhibit heteropycnosis.|
|Replicative||Heterochromatin is a late replicative that replicate later than euchromatin.||Euchromatin is an early replicative that replicate earlier than euchromatin.|
|Genetic processes||Heterochromatin is not affected by genetic processes where the alleles are not varied.||Euchromatin is affected by various genetic processes that result in variation within the alleles.|
|Function||Heterochromatin maintains the structural integrity of the genome and allows the regulation of gene expression.||Euchromatin allows the genes to be transcribed and variation to occur within the genes.|
|Examples||Telomeres and centromeres, Barr bodies, one of the X chromosomes, genes 1, 9, and 16 of humans are some examples of heterochromatin.||All the chromosomes in the genome except the heterochromatin are examples of euchromatin.|
References and Sources
- Murakami Y. (2013) Heterochromatin and Euchromatin. In: Dubitzky W., Wolkenhauer O., Cho KH., Yokota H. (eds) Encyclopedia of Systems Biology. Springer, New York, NY
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