Chromatin
Chromatin
Chromatin (/kroʊˈmætɪn/; from Ancient Greek: χρῶμα, romanized: chrôma, lit. 'color') is a complex of DNA and protein that condenses to form chromosomes within the nucleus of eukaryotic cells.
Etymology
The term "chromatin" is derived from the Greek word "chroma" meaning color, as it can be stained with dyes to make it visible under a microscope. It was first used by German biologist Walther Flemming in 1882.
Structure
Chromatin is composed of nucleosomes, which are repeating units of DNA wrapped around eight histone proteins. This structure allows the long DNA molecules to fit within the cell nucleus and also plays a crucial role in gene regulation.
Types
There are two types of chromatin: euchromatin and heterochromatin. Euchromatin is less condensed and is actively transcribed, while heterochromatin is more condensed and is typically transcriptionally inactive.
Function
The primary function of chromatin is to efficiently package DNA into a small volume to fit into the nucleus of a cell and protect the DNA structure and sequence. Chromatin also controls gene expression and DNA replication, repair, and recombination.
Related Terms
- Epigenetics: The study of changes in organisms caused by modification of gene expression rather than alteration of the genetic code itself. Chromatin plays a key role in these processes.
- Histone modification: A covalent post-translational modification to histone proteins which includes methylation, phosphorylation, acetylation, ubiquitylation, and sumoylation. The modifications can alter chromatin structure and regulate gene expression.
- Nucleosome: The basic unit of DNA packaging in eukaryotes, consisting of a segment of DNA wound in sequence around eight histone protein cores.
External links
- Medical encyclopedia article on Chromatin
- Wikipedia's article - Chromatin
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