fokiroute.blogg.se - Chromatin crossover definition genetics

I’ll retain the name Chromatin as long as Chemistry has decided about it, and I empirically refer to it as that substance in the cell's nucleus which takes up the dye upon staining the nucleus ("Kerntinktionen").

It is possible that this substance is really identical with the Nuclein-bodies. from German): “The scaffold owes its capability of refraction, the way how it behaves, and in particular its colorability to a substance which, with regard to its latter attribute, I have termed Chromatin. Furthermore, there were nucleoli, the nuclear plasm and the nuclear membranes. Flemming assumed that within the nucleus there was some kind of nuclear-scaffold. In 1882 Walther Flemming used the term chromatin for the first time. The changes in structure are required to allow the DNA to be used and managed, whilst minimising the risk of damage. The structure of chromatin varies considerably as the cell progresses through the cell cycle. Recent evidence however, has revealed that these traditional fixed views of chromatin are not strictly correct and that both active and inactive genes can be found within chromatin regions of either type. These correspond to uncompacted actively transcribed DNA and compacted untranscribed DNA. In non-dividing cells there are two types of chromatin: euchromatin and heterochromatin. The different levels of chromatin compaction are clearly visible in cells. These structures do not occur in all eukaryotic cells there are examples of more extreme packaging, for example spermatozoa and avian red blood cells.

Higher level DNA packaging into the metaphase chromosome.

A 30 nm condensed chromatin fiber consisting of nucleosome arrays in their most compact form.

DNA wrapping around nucleosomes - The "beads on a string" structure.

Simplistically, there are three levels of chromatin organization (Fig.

4.4 Spatial organization of chromatin in the cell nucleus.

4.2 The nucleosome and "beads-on-a-string".

Chromatin structure is also relevant to DNA replication and DNA repair.Ĭhromatin is easily visualised by staining, hence its name, which literally means coloured material. Changes in chromatin structure are affected mainly by methylation (DNA and proteins) and acetylation (proteins). The functions of chromatin are to package DNA into a smaller volume to fit in the cell, to strengthen the DNA to allow mitosis and meiosis, and to serve as a mechanism to control expression. The major proteins involved in chromatin are histone proteins, although many other chromosomal proteins have prominent roles too. It is found inside the nuclei of eukaryotic cells, and within the nucleoid in prokaryotes. If a more appropriate WikiProject or portal exists, please adjust this template accordingly.Ĭhromatin is the complex of DNA and protein that makes up chromosomes.

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