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

Histone degradation after DNA damage enhances repair

DNA damage can occur anywhere in the genome, but most DNA is wrapped around nucleosomes making it inaccessible to the repair machinery. Researchers from the Gasser group now show that DNA damage induces histone depletion, ...

How cGAS enzyme is kept bottled up

In higher organisms, detection of DNA in the cytoplasm triggers an immune reaction. The enzyme that senses "misplaced" DNA is also found in the nucleus, but nuclear DNA has no such effect. LMU researchers now report why that ...

FloChiP, a new tool optimizing gene-regulation studies

In the cell, proteins often interact directly with DNA to regulate and influence the expression of genes. For this to happen, proteins need to travel into the cell's nucleus where the DNA is tightly twisted and packed as ...

New method reveals where DNA is at risk in the cell

Researchers at Karolinska Institutet have developed a new sequencing method that makes it possible to map how DNA is spatially organized in the cell nucleus—revealing which genomic regions are at higher risk of mutation ...

New technology will show how RNA regulates gene activity

The discovery of a huge number of long non-protein coding RNAs, aka lncRNAs, in the mammalian genome was a major surprise of the recent large-scale genomics projects. An international team including a bioinformatician from ...

Novel system reveals mechanisms of pluripotency transition

In a study published online in Nature Cell Biology on May 11, scientists from Guangzhou Institute of Biomedicine and Health (GIBH) of the Chinese Academy of Sciences established a novel and efficient system for non-integrated ...

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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