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

Researchers study the intricate processes underpinning gene expression

A new study led by University of Maryland physicists sheds light on the cellular processes that regulate genes. Published in the journal Science Advances, the paper explains how the dynamics of a polymer called chromatin—the ...

A glimpse into the hexasome: 40 years on

In 1983, scientists discovered hexasomes—a unique molecular structure that helps cells package their DNA. Now, a study conducted by the Eustermann group at EMBL Heidelberg has shed light on how DNA packaging into hexasomes ...

Team proposes a new view on euchromatin in the cell

Scientists studying cells have long held the view that euchromatin, the part of chromatin that is made up of genes and is genetically active, is open and can be transcribed. A research team, looking at new evidence from genomics ...

DNA packaging supports cell division, finds study

The DNA molecule is located in the cell nucleus as a densely packed complex of DNA and protein, known as chromatin. Wrapped in sections around a core of special proteins known as histones, the DNA forms so-called nucleosomes, ...

Euchromatin is not really open in living cells, shows study

DNA and associated proteins in active regions of the genome are condensed but behave like a viscous liquid at the molecular level. This finding greatly increases our understanding of the physical nature of expressed genome ...

Study: SARS-CoV-2 can alter genome structure of our cells

People infected with SARS-CoV-2, the virus that causes COVID-19, may experience genome structure changes that not only may explain our immunological symptoms after infection, but also potentially link to long COVID, according ...

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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.

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