Nucleoid
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In prokaryotes, the nucleoid (meaning nucleus-like and also known as the nuclear region, nuclear body or chromatin body) is an irregularly shaped region within the cell where the genetic material is localised. The nucleic acid is a circular, double-stranded piece of DNA and multiple copies may exist. This method of genetic storage can be contrasted against that of the eukaryotes, where DNA is packed into chromosomes and sequestered within a membrane-bound organelle called the nucleus. The nucleoid can be clearly visualised on an electron micrograph at high magnification, where although its appearance may differ, it is clearly visible against the cytosol. Sometimes even strands of what is thought to be DNA are visible. By staining with the Feulgen stain, which specifically stains DNA, the nucleoid can also be seen under a light microscope. It is also near the nucleay in a prokaryotic cell.
[edit] Composition
Experimental evidence suggests that the nucleoid is largely composed of DNA, about 60%, with a small amount of RNA and protein. The latter two constituents are likely to be mainly messenger RNA and the transcription factor proteins found regulating the bacterial genome. Proteins helping to maintain the supercoiled structure of the nucleic acid are known as nucleoid proteins and are distinct from the functionally similar histones present in eukaryotic nuclei.
[edit] See also
[edit] References
- Prescott, L. (1993). Microbiology, Wm. C. Brown Publishers, ISBN 0-697-01372-3
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