Genetics

Scientists find molecular key to body making healthy T cells

In a finding that could help lead to new therapies for immune diseases like multiple sclerosis and IBD, scientists report in the Journal of Experimental Medicine identifying a gene and family of proteins critical to the formation ...

Genetics

How your DNA takes shape makes a big difference in your health

The more we learn about our genome, the more mysteries arise. For example, how can people with the same disease-causing mutation have different disease progression and symptoms? And despite the fact that it's been more than ...

Medical research

A moderate dose of novel form of stress promotes longevity

A newly described form of stress called chromatin architectural defect, or chromatin stress, triggers in cells a response that leads to a longer life. Researchers at Baylor College of Medicine and the Houston Methodist Research ...

Oncology & Cancer

Study identifies link between DNA-protein binding, cancer onset

Researchers at the Stanford University School of Medicine and their collaborators at other institutions have identified a link between how proteins bind to our DNA and how cancer develops. This finding may allow researchers ...

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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