Euchromatin is a lightly packed form of
chromatinthat is rich in geneconcentration, and is often (but not always) under active transcription. Unlike heterochromatin, it is found in both eukaryotesand prokaryotes.
The structure of euchromatin is reminiscient of an unfolded set of beads along a string, where those beads represent
nucleosomes. Nucleosomes consist of eight proteins known as histones, with approximately 147 base pairsof DNAwound around them; in euchromatin this wrapping is loose so that the raw DNA may be accessed. Each core histone possesses a `tail' structure which can vary in several ways; it is thought that these variations act as "master control switches" which determine the overall arrangement of the chromatin. In particular, it is believed that the presence of methylated lysine 4 on the histone tails acts as a general marker for euchromatin.
Euchromatin generally appears as light-colored bands when stained in
GTG bandingand observed under an optical microscope; in contrast to heterochromatin, which stains darkly. This lighter staining is due to the less compact structure of euchromatin. It should be noted that in prokaryotes, euchromatin is the "only" form of chromatin present; this indicates that the heterochromatin structure evolved later along with the nucleus, possibly as a mechanism to handle increasing genome size
Euchromatin participates in the active transcription of DNA to
mRNAproducts. The unfolded structure allows gene regulatory proteins and RNA polymerasecomplexes to bind to the DNA sequence, which can then initiate the transcription process. Not all euchromatin is necessarily transcribed, but in general that which is not is transformed into heterochromatinto protect the genes while they are not in use. There is therefore a direct link to how actively productive a cell is and the amount of euchromatin that can be found in its nucleus. It is thought that the cell uses transformation from euchromatin into heterochromatin as a method of controlling gene expression and replication, since such processes behave differently on densely compacted chromatin- this is known as the `accessibility hypothesis'. One example of constitutive euchromatin that is 'always turned on' is housekeeping genes, which codes for the proteins needed for basic functions of cell survival.
External links and references
* [http://chromatin.co.uk/Euchromatin.html Research news in Euchromatin]
* [http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=154571 Article]
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Look at other dictionaries:
euchromatin — euchromatin. См. эухроматин. (Источник: «Англо русский толковый словарь генетических терминов». Арефьев В.А., Лисовенко Л.А., Москва: Изд во ВНИРО, 1995 г.) … Молекулярная биология и генетика. Толковый словарь.
Euchromatin — das, s, die nur schwach anfärbbaren Chromosomenabschnitte, Chromosomen … Universal-Lexikon
Euchromatin — Euchromatin, beim Übergang vom Teilungskern zum Interphasekern sich auflockerndes Chromatin, schwächer anfärbbar als das kondensierte ⇒ Heterochromatin, wird in der Interphase vor dem Heterochromatin repliziert. Nur das E. wird transkribiert … Deutsch wörterbuch der biologie
euchromatin — [yo͞o krō′mə tin] n. [Ger: see EU & CHROMATIN] Biol. the portion of the chromatin that accepts a light stain and contains most of the active genetic material: cf. HETEROCHROMATIN … English World dictionary
Euchromatin — Das Euchromatin stellt die Bereiche des aufgelockerten Chromatingerüsts im Karyoplasma einer Zelle dar. Im Gegensatz zum Heterochromatin liegt die Desoxyribonucleinsäure (DNA) hier in weniger dicht gepackter Form vor. Im Euchromatin befinden sich … Deutsch Wikipedia
euchromatin — noun Etymology: International Scientific Vocabulary Date: 1932 the part of chromatin that is genetically active and is largely composed of genes • euchromatic adjective … New Collegiate Dictionary
euchromatin — The chromosomal regions that are diffuse during interphase and condensed at the time of nuclear division. They show what is considered to be the normal pattern of staining (eu = true) as opposed to heterochromatin … Dictionary of molecular biology
euchromatin — euchromatic /yooh kreuh mat ik/, adj. /yooh kroh meuh tin/, n. Genetics. the part of a chromosome that condenses maximally during metaphase and contains most of the genetically active material. [1930 35; EU + CHROMATIN] * * * … Universalium
euchromatin — noun uncoiled dispersed threads of chromosomal material that occurs during interphase; it stains lightly with basic dyes … Wiktionary
euchromatin — The parts of chromosomes that, during interphase, are uncoiled dispersed threads and not stained by ordinary dyes; metabolically active, in contrast to the inert heterochromatin. * * * eu·chro·ma·tin ( )yü krō mət ən n the genetically active… … Medical dictionary