Heterochromatin Vs Euchromatin: The human genome consists of over 3 billion base couples or nucleotides. These nucleotides, which are arranged in a linear arrangement along with DNA (deoxyribonucleic acid), encode every protein and genetic trait in the human body. This information is contained in almost 20,000 genes which, surprisingly, mean only a small fraction (about 1.5%) of the total DNA. The rest is comprised of non-coding sequences. The principle of the genetic sequence is necessary for normal cell function and that is highlighted when genetic anomalies go unexplored by intrinsic genetic repair mechanisms and give acceleration to dysfunctional proteins and various diseases states.
In the interphase nucleus, chromosomes are troublesome to analyze from each other. Nevertheless, they do involve a discrete space inside a nucleus – a so-called chromosome area. Lighter-stained euchromatin (transcriptionally active) and the bits of darker heterochromatin (transcriptionally silent) are, on the other hand, easy to envision. During the cell division, chromosome territories convert into extremely condensed chromosomes, which then can be clearly categorized from one another. Together, mitotic chromosomes, visualized in the light microscope, are named karyotypes.
A series of mechanisms must therefore take area that enables the cell to package DNA within the confines of the nucleus whilst maintaining its capability to transcribe and clone the entire DNA sequence and hold its integrity. This is achieved through a complicated process of DNA condensation that identifies DNA packaged into 46 chromosomes (or 23 chromosome pairs) in humans. The number of chromosomes differs from species to species; for example, there are 40 chromosomes (20 pairs) in mice, 8 chromosomes (4 pairs) in the popular fruit fly, and 10 chromosomes (5 pairs) in the Arabidopsis thaliana plant.
Chromosomes reach their greatest level of condensation during cell division, or mitosis, where they will achieve a discrete 4-armed or 2-armed morphology that displays almost 10,000-fold compaction. Although this densely condensed mitotic form has become the most familiar way of characterizing chromosomes, their structure is significantly disparate during the interphase. Correlated to mitotic chromosomes, interphase chromosomes are less condensed and take up the entire nuclear space, making them somewhat challenging to distinguish.
Like the construction of metaphase chromosomes, the compaction lacked to fit a full set of interphase chromosomes into the nucleus is accomplished through a series of DNA folding, wrapping, and curling events that are facilitated by histones, which are eminently maintained basic nuclear proteins that enable DNA compaction by counterbalancing DNA’s negative charge. Histones mainly arrange as an octamer in complex with DNA to form the nucleosome. The combination of DNA and histone proteins that make up the nuclear content is frequently referred to as chromatin.
What Is Heterochromatin?
Heterochromatin is a tightly crowded or condensed DNA that is characterized by extraordinary stains when stained with nuclear stains, consisting of transcriptionally inactive sequences.
- It remains in multiple variations, up to four to five states, each of which is signified with combinations of epigenetic markers.
- The blotch of heterochromatin might appear in heteropycnosis; heteropycnosis is the differential staining of parts of chromosomes.
- This chromosome is disparate from euchromatin in that the genes in these chromosomes are commonly inactivated and are not indicated.
- Heterochromatin is present in the nucleus towards the boundary. It is also not present in prokaryotic cells, expressing this form that arrived later during evolution.
- However, the two most remarkably familiar heterochromatin include; constitutive heterochromatin and facultative heterochromatin.
- Constitutive heterochromatin usually packages the uniform arrangements of DNA in all cells of the same species. It is usually repetitive and is present in structural forms like telomeres and centromeres.
- The genes in constitutive heterochromatin might disturb the genes present near the tightly packed chromosomes.
- In humans, genes 1, 9, 16, and the Y chromosomes in men consist of larger quantities of this heterochromatin.
- Facultative heterochromatin packages genes that are commonly silenced through various mechanisms; however, unlike constitutive heterochromatin, facultative chromatin packages differ genes in different organisms within the ditto species.
- The facultative chromosome is not repeated but has the same structural components as the constitutive heterochromatin.
- The formation of facultative heterochromatin is administered by the process of morphogenesis or differentiation.
- In humans, one of the two X chromosomes in women is inactivated as facultative heterochromatin while the other is expressed as euchromatin.
- Heterochromatin has multiple functions. Some of which consist of gene regulation and chromosomes integrity.
- The tightly packaged DNA in heterochromatin prevents the chromosomes from various protein factors that might lead to the binding of DNA or the inaccurate destruction of chromosomes by endonucleases.
- Besides, heterochromatin also allows gene regulation and the inheritance of epigenetic markers.
What Is Euchromatin?
Euchromatin is a more delicately packed DNA that is characterized by less intense staining and DNA arrangements that are transcriptionally active or might become transcriptionally active at some point during improvement.
- Euchromatin is available towards the center of the nucleus and accounts for about 90% of the genome in an organism.
- Under an optical microscope, it arrives as light-colored bands after staining. All parts of euchromatin are consistently stained, which doesn’t result in heteropycnosis.
- Under an electron microscope, however, it emerges as an elongated 10 nm microfibril.
- The format of the euchromatin can be made as an unfolded collection of beads in a string where the beads are the nucleosomes. The nucleosomes accommodate histone proteins that coat a particular number of DNAs around.
- In euchromatin, the wrapping around by histone proteins is relaxed, and thus the individual DNA sequences might be reachable.
- The conformation of euchromatin is claimed to be administered by a methylated part in the chromosome called the histone tail.
- Euchromatin is the only confirmation of chromosomes in the case of the prokaryotic genome, which proposes that this form derived earlier than heterochromatin.
- Unlike heterochromatin, euchromatin doesn’t exist in two patterns. It only exists as constitutive euchromatin.
- Euchromatin is utterly essential as it contains genes that are transcripted into RNA, which are then translated into proteins.
- The unfolded structure of DNA in euchromatin allows regulatory proteins and RNA polymerase to bind to the sequences so that the mechanism of transcription can initiate.
- It is achievable for some genes in the euchromatin to be transformed into heterochromatin when they are not to be transcribed and are no longer active.
- The conversion of euchromatin to heterochromatin acts as a form for regulating gene expression and replication.
- For this purpose, some genes like housekeeping genes are always arranged in euchromatin surity as they have to be continuously replicated and transcribed.
Heterochromatin vs 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. while 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 while 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 the 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.
The process of DNA to protein formation is a complex one! Many enzymes, DNA sequences, and regulatory elements are involved in it. The transition from the euchromatin region to heterochromatin plays an important role in gene expression.
An abnormal euchromatin profile or heterochromatin profile may cause several health problems. Conclusively, the main difference between the euchromatin and heterochromatin regions is their role in transcription. One is transcriptionally active while another is transcriptionally active.
The overall function of chromatins is to form protein and regulate the expression of genes.