Similarities and Differences of Heterochromatin, Euchromatin and Transposons

Over 3 billion base pairs, or nucleotides, make up the human genome. Every protein and genetic feature in the human body is encoded by these nucleotides, which are arranged in a linear sequence along DNA (deoxyribonucleic acid). This information is housed in roughly 20,000 genes, which, interestingly, account for just about 1.5 percent of total DNA. Non-coding sequences make up the rest of the genome. The integrity of the genetic sequence is critical for appropriate cell function, as evidenced by the fact that genetic aberrations go undetected by intrinsic genetic repair systems, resulting in defective proteins and illnesses.

Steps Involved in Packaging DNA

As a result, a number of steps must occur to allow the cell to package DNA into the nucleus while maintaining its ability to transcribe and replicate the full DNA sequence while maintaining its integrity. This is accomplished through a complex DNA condensation process, in which DNA is packaged into 46 chromosomes (or 23 chromosome pairs) in humans. The number of chromosomes varies by species; for example, mice have 40 chromosomes (20 pairs), the common fruit fly has 8 chromosomes (4 pairs), and the Arabidopsis thaliana plant has 10 chromosomes (5 pairs).

Mitosis of Chromosomes

During cell division, or mitosis, chromosomes attain their maximum amount of condensation, acquiring a discrete 4-armed or 2-armed shape that indicates nearly 10,000-fold compaction.

 Despite the fact that this heavily condensed mitotic shape has been the most frequent manner of representing chromosomes, their structure during the interphase is significantly different. Interphase chromosomes are less condensed than mitotic chromosomes and occupy the full nuclear region, making them difficult to differentiate.

Change in Interphase of Chromosome

The compaction required to fit a full set of interphase chromosomes into the nucleus, like that required to fit a full set of metaphase chromosomes into the nucleus, is facilitated by histones, which are highly conserved basic nuclear proteins that enable DNA compaction by neutralising DNA’s negative charge. Histones form the nucleosome when they form an octamer in combination with DNA. Chromatin is the name given to the mixture of DNA and histone proteins that make up the nuclear material.

Euchromatin vs Heterochromatin

Depending on the degree of compaction, interphase chromatin is characterised as either euchromatin or heterochromatin. Euchromatin has a less compact structure and is commonly described as an 11 nm fibre that resembles “beads on a string,” with the beads representing nucleosomes and the string representing DNA. Heterochromatin, on the other hand, is more compact, and is commonly described as a nucleosome array condensed into a 30 nm fibre. However, the 30 nm fibre has never been seen in vivo, and its existence is debatable.

The condensation of DNA, which encodes the genetic information of the cell, is obviously more sophisticated than can be described by simple 11 nm or 30 nm fibre models. Throughout the cell cycle, transcription equipment requires access to genetic information, whereas replication machinery copies DNA during S-phase. The distinctions between euchromatin and heterochromatin, as well as the placement of chromatin within the nucleus, demonstrate this increased complexity.

The presence of repetitive DNA elements such as satellite sequences and transposable elements within heterochromatin, particularly in the highly condensed centromeres and telomeres, reflects the fact that intrinsic mechanisms exist in the condensation of DNA to control access for transcriptional or replication purposes. Constitutive heterochromatin is a type of heterochromatin that remains condensed throughout the cell cycle and is not actively transcribed. On the other hand, facultative heterochromatin, which can be unravelled to produce euchromatin, is more dynamic, forming and changing in response to cellular signals and gene activity . During the cell cycle, this area often includes genetic material that will be transcribed.

Euchromatin and Heterochromatin

• Both are DNA sequences built up of polynucleotide chains, but they serve different purposes
• The primary nucleosome assembly is used to organise both on chromosomes
• During the interphase stage of cell division, the euchromatin and heterochromatin are more evident

Transposable

Nearly all eukaryotes have transposable elements in their genomes. The Berkeley Drosophila Genome Project recently completed the release of 3 euchromatic genomic sequences of Drosophila melanogaster, which revealed an accurate sequence for the repeated elements in Drosophila euchromatin. The euchromatic transposable elements in the sequenced strain of this species were described using this genomic sequence.

Conclusion

Over 3 billion base pairs, or nucleotides, make up the human genome. Every protein and genetic feature in the human body is encoded by these nucleotides, which are arranged in a linear sequence along DNA (deoxyribonucleic acid). This information is housed in roughly 20,000 genes, which, interestingly, account for just about 1.5 percent of total DNA. 

Non-coding sequences make up the rest of the genome. The integrity of the genetic sequence is critical for appropriate cell function, as evidenced by the fact that genetic aberrations go undetected by intrinsic genetic repair systems, resulting in defective proteins and illnesses.