Heterochromatin
Heterochromatin
Heterochromatin (pronounced: /ˌhɛtəroʊˈkroʊmətɪn/) is a type of chromatin that is densely packed and transcriptionally inactive.
Etymology
The term "heterochromatin" is derived from the Greek words "heteros" meaning different, and "chroma" meaning color. This is due to the fact that heterochromatin stains more intensely than other types of chromatin during interphase.
Description
Heterochromatin is a tightly packed form of DNA, which comes in multiple varieties. These varieties lie on a continuum between the two extremes of constitutive heterochromatin and facultative heterochromatin. Both play a role in the expression of genes. Because it is tightly packed, it was originally thought to be inaccessible to polymerases and therefore not transcribed into RNA.
Constitutive Heterochromatin
Constitutive heterochromatin is a form of heterochromatin that is always compact and not expressed. It is found around the centromere and telomeres of all chromosomes.
Facultative Heterochromatin
Facultative heterochromatin is a form of heterochromatin that can convert into euchromatin. It is not always in a compact state. The inactivation of the X chromosome in female mammals is an example of this type of heterochromatin.
Related Terms
- Euchromatin: The less condensed form of chromatin that is available for transcription.
- Chromosome: A DNA molecule with part or all of the genetic material of an organism.
- Gene expression: The process by which information from a gene is used in the synthesis of a functional gene product.
- Centromere: The part of a chromosome that links sister chromatids.
- Telomere: A region of repetitive nucleotide sequences at each end of a chromosome, which protects the end of the chromosome from deterioration or from fusion with neighboring chromosomes.
External links
- Medical encyclopedia article on Heterochromatin
- Wikipedia's article - Heterochromatin
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