News tagged with chromatin

Related topics: protein , genes , gene expression , dna , cell nucleus

Recycling histones through transcription

Cells reuse a part of the histones which are used to pack DNA, according to a current study by Karolinska Institutet. The study, which is published in the journal Genome Research, was conducted on yeast cells, but it is ...

Mar 26, 2015
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Predicting cancers' cell of origin

A study led by researchers from Brigham and Women's Hospital suggests a new way to trace cancer back to its cell type of origin. By leveraging the epigenome maps produced by the Roadmap Epigenomics Program ...

Feb 18, 2015
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Genome packaging: Key to breast cancer development

Cancer is a complex disease and only thanks to advances in genomic techniques have researchers begun to understand, at a cellular and molecular level, the mechanisms which are disrupted in cancer cells. This ...

Nov 22, 2012
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Chromatin

Chromatin is the combination of DNA and proteins that make up the contents of the nucleus of a cell. The primary 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 prevent DNA damage, and to control gene expression and DNA replication. The primary protein components of chromatin are histones that compact the DNA. Chromatin is only found in eukaryotic cells: prokaryotic cells have a very different organization of their DNA which is referred to as a genophore (a chromosome without chromatin).

The structure of chromatin depends on several factors. The overall structure depends on the stage of the cell cycle: during interphase the chromatin is structurally loose to allow access to RNA and DNA polymerases that transcribe and replicate the DNA. The local structure of chromatin during interphase depends on the genes present on the DNA: DNA coding genes that are actively transcribed ("turned on") are more loosely packaged and are found associated with RNA polymerases (referred to as euchromatin) while DNA coding inactive genes ("turned off") are found associated with structural proteins and are more tightly packaged (heterochromatin). Epigenetic chemical modification of the structural proteins in chromatin also alter the local chromatin structure, in particular chemical modifications of histone proteins by methylation and acetylation. As the cell prepares to divide, i.e. enters mitosis or meiosis, the chromatin packages more tightly to facilitate segregation of the chromosomes during anaphase. During this stage of the cell cycle this makes the individual chromosomes in many cells visible by optical microscope.

In general terms, there are three levels of chromatin organization:

There are, however, many of cells which do not follow this organisation. For example spermatozoa and avian red blood cells have more tightly packed chromatin than most eukaryotic cells and trypanosomatid protazoa do not condense their chromatin into visible chromosomes for mitosis.

This text uses material from Wikipedia licensed under CC BY-SA