Mapping the development of infection-fighting immune cells

The immune system protects the body from invaders, such as bacteria, viruses, or tumors, with its intricate network of proteins, cells, and organs. Specialized immune cells, called cytotoxic T cells, can develop into short-lived ...

Oncology & Cancer

How genome doubling helps cancer develop

A single cell contains 2-3 meters of DNA, meaning that the only way to store it is to package it into tight coils. The solution is chromatin: a complex of DNA wrapped around proteins called histones. In the 3D space, this ...

Medical research

How pancreatic cancer defies treatment by leveraging a protein

Pancreatic cancer is the third deadliest cancer in the United States, after lung and colorectal, though far less common. It is also among the hardest to effectively treat, with pancreatic cancer stem cells quickly developing ...


3D map reveals DNA organization within human retina cells

National Eye Institute researchers mapped the organization of human retinal cell chromatin, the fibers that package 3 billion nucleotide-long DNA molecules into compact structures that fit into chromosomes within each cell's ...


Researchers use DNA analysis to diagnose subtypes of heart disease

The human heart is an intricate, complex organ and, like a car that starts sputtering, its function deteriorates for all sorts of reasons. Cardiomyopathy—any disease of the heart muscle that makes it pump blood less effectively—can ...

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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.

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