Euchromatin

A loose aggregation form of chromatin

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often Chromatin Is chromatin (from DNA 、 RNA and protein Composition), which is a loose aggregation form. This aggregation mode exists in a large number of genes, and the corresponding fragments are usually in the active transcription (but not necessary, that is, the euchromatin is not necessarily a highly expressed sequence). Euchromatin nucleus genome The most active part of.

human genome 92% of them are euchromatin^[1] 。

Chinese name: Euchromatin
Foreign name: euchromatin

Nature: Low folding and compression degree of chromatin fiber
Chemical essence: DNA, RNA and protein
DNA packaging: The ratio is about 1/2000-1/1000

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structure

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The structure of euchromatin is similar to that of an unfolded string of beads, which are passed through by a string Nucleosome structure 。 each Nucleosome By eight protein Monomer composition, these proteins are called Histone 147 around each histone monomer Base pair Lengthwise Double chain DNA Surround; In euchromatin, the package of DNA on histone is relatively loose, so the original DNA sequence It is exposed and can be read. Each is surrounded by DNA core histone Monomer (in addition to the 8 core histones wrapped by DNA Connexin Histone H1, etc.) has a "tail" polypeptide structure, which can be modified in various degrees. These tail decorations are believed to play a role gene regulation They can determine the density of the whole gene on the chromosome. One specific example of this is when Lysine (K4), which is an important class of markers on histones.

appearance

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Chromatin can be divided into two groups, Heterochromatin And euchromatin. At the beginning, the two forms are distinguished by their color after dyeing. The euchromatin is generally slightly colored, while the heterochromatin is deeply colored, indicating that it is closely clustered. Heterochromatin is usually concentrated in the marginal region of the nucleus. However, unlike this early dichotomy Recent research shows that there are more than two kinds of chromosome structures in animals and plants. There may be four to five kinds of chromosome structures. The difference lies in their appearance genetic marker Is different.

In general, euchromatin passes through G banding The technology is represented by light colored ribbons. Such structures are optical microscope As can be seen below, its color is different from that of darker heterochromatin. The light staining is due to the low degree of aggregation. Autosome Of Basic structure It is a slender, open and unfolded 10 nanometer long microfiber. stay Prokaryotic cell The euchromatin is the only chromatin Existing form ； This indicates that heterochromatin is a structure evolved after prokaryotic cells together with the nucleus, and may also be a solution Eukaryotic cell Bigger and Bigger genome Mechanism of conflict with limited nuclear space.

function

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Genes in the euchromatin region can be transcribed into Messenger RNA 。 The unfolded structure of the euchromatin region allows gene regulatory proteins and RNA polymerase It binds to the DNA sequence on it to start the transcription process. In the process of transcription, not all euchromatin will be transcribed, but basically the non transcribed part will be folded into heterochromatin to protect genes not used on it temporarily. Therefore, the activity of the cell and the constant staining in the nucleus Prime number The item has a direct relationship.

The conversion between euchromatin and heterochromatin is considered as a regulation gene expression And replication mechanism. This is based on the "accessibility hypothesis". It is more difficult to complete gene transcription and expression in tightly compressed chromatin, which requires an additional mechanism. Therefore, genes on loosely clustered euchromatin regions are easier to replicate and transcribe. Such structures are particularly important for some genes with high expression levels. A class of frequently active structural euchromatin is a gene (also called Housekeeper gene ， housekeeping genes）。

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