Chromatin
Chromatin, or nuclear material, is a complex of DNA and proteins that together form a nucleohistone (chromosome) thread. In the nucleus, where nuclear division does not take place, chromatin is found in 2 forms, heterochromatin and euchromatin.
Heterochromatin and Euchromatin[edit | edit source]
If we stained the nuclear mass with nuclear dyes, "euchromatin" appears as a lighter, i.e. more transcriptionally active part (the fiber is more relaxed) when stained with nuclear dyes. The parts that turn darker are called heterochromatin, they are places where transcription is not active. Heterochromatin is further divided into:
- constitutive – permanently inactive sections of DNA (typical are large heterochromatin blocks on chromosomes 1, 9, 16 and Y[1]);
- optional - currently inactive sections (under certain conditions they can resume their function) e.g. developmental genesy.
Structure of Chromatin[edit | edit source]
- DNA
- Specific proteins - Histones and non-histone proteins
The DNA double helix is wrapped around the histone octamers H2A, H2B, H3, H4. Histone H1 forms a link between these formations. This whole thing together (DNA, histone octamer and histone H1) forms a 'nucleosome.
Nucleosome[edit | edit source]
It represents the basic building block of the chromosome (nucleohistone) fiber. Several nucleosomes in a row form formations similar to beads on a thread - so-called polynucleosomes.
Histones[edit | edit source]
For more information see Histones.In addition to the construction function, they also have a regulatory function. It forms the histone code. They are involved in the regulation of gene expression as one of many epigenetic modifications.
E.g.:
- methylation of a lysine residue on H3 stops expression
- acetylation of a lysine residue on H3 initiates transcription
- and others: phosphorylation, ubiquitinization, ADP ribosylation affecting expression regulation as well as chromatin condensation and decondensation
Links[edit | edit source]
Related Articles[edit | edit source]
References[edit | edit source]
- ↑ KOWALCZYK, Małgorzata – SREBNIAK, Małgorzata – TOMASZEWSKA, Agnieszka. Chromosome abnormalities without phenotypic consequences. J Appl Genet [online]. 2007, vol. 48, no. 2, p. 157-66, Available from <https://www.ncbi.nlm.nih.gov/pubmed/17495350>. ISSN 1234-1983.
References[edit | edit source]
- STROLLER, Eduard – MR, Martin. Clinical Cytogenetics I : introduction to clinical cytogenetics. 2. edition. Prague : Karolinum, 2010. ISBN 978-80-246-1880-7.
