7.6:
Euchromatin
In eukaryotes, chromatin exists in two primary forms based on its compaction level – euchromatin and heterochromatin.
During interphase, the euchromatin is dispersed in the nucleus and replicated throughout the S phase of the cell cycle.
Euchromatin is a gene-rich, less compact, and actively transcribed region of the chromatin. When fixed and viewed under a microscope, it appears as lightly stained regions because it can retain fewer stain particles.
In metaphase chromosomes, the lightly stained regions represent the euchromatin.
The histone tail amino acids of euchromatin are extensively acetylated. Acetylation increases the negative charge on histone proteins, locally reducing the histone-DNA affinity. This reduces the chromatin compaction, allowing easier access to DNA.
7.6:
Euchromatin
The extent of chromatin compaction can be studied by staining chromatin using specific DNA binding dyes. Under the microscope, the dense-compacted regions take up more dye, appearing darker, while the less-compact areas take up less dye and appear lighter. Based on the compaction level, chromatins are classified into two primary forms – euchromatin and heterochromatin.
Euchromatin is the less dense region of the chromatin and stains lighter. Euchromatin contains histone H3 extensively acetylated on lysine at the 9th position of the histone tail region. Histones in the promoter region have methylated lysine 4 and phosphorylation of position 10. Extensive acetylation reduces the attraction between histones and DNA, loosening the chromatin. During interphase, the euchromatin can be found dispersed throughout the cell nucleus. It replicates during the entire duration of the S-phase of cell division.
Leitura Sugerida
- Molecular Biology of Cell, Alberts, 6th edition, Pages 210-211
- Molecular Cell Biology, Lodish, 8th edition, Pages 333-341.
- Filion, Guillaume J., Joke G. van Bemmel, Ulrich Braunschweig, Wendy Talhout, Jop Kind, Lucas D. Ward, Wim Brugman et al. "Systematic protein location mapping reveals five principal chromatin types in Drosophila cells." Cell 143, no. 2 (2010): 212-224.