Nucleoid


Nucleoid
Prokaryote cell showing the nucleoid.

The nucleoid (meaning nucleus-like) is an irregularly-shaped region within the cell of a prokaryote that contains all or most of the genetic material.[1] In contrast to the nucleus of a eukaryotic cell, it is not surrounded by a nuclear membrane. The genome of prokaryotic organisms generally is a circular, double-stranded piece of DNA, of which multiple copies may exist at any time. The length of a genome widely varies, but generally is at least a few million base pairs.

A genophore is the DNA of a prokaryote. It is commonly referred to as a prokaryotic chromosome. The term "chromosome" is misleading for a genophore because the genophore lacks chromatin.[2] The genophore is compacted through a mechanism known as supercoiling,[3] whereas a chromosome is compacted via chromatin. The genophore is circular in most prokaryotes, and linear in very few. The circular nature of the genophore allows replication to occur without telomeres.[4] Genophores are generally of a much smaller size than Eukaryotic chromosomes. A genophore of a true organism can be as small as 580,073 base pairs (Mycoplasma genitalium). Many eukaryotes (such as plants and animals) carry genophores in organelles such as mitochondria and chloroplasts. These organelles are very similar to true prokaryotes.[5]

Contents

Visualization

The nucleoid can be clearly visualized 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. The DNA-intercalating stains DAPI and ethidium bromide are widely used for fluorescence microscopy of nucleoids.

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 or nucleoid-associated proteins and are distinct from histones of eukaryotic nuclei. In contrast to histones, the DNA-binding proteins of the nucleoid do not form nucleosomes, in which DNA is wrapped around a protein core. Instead, these proteins often use other mechanisms to promote compaction such as DNA looping.

See also

References

  1. ^ Thanbichler M, Wang S, Shapiro L (2005). "The bacterial nucleoid: a highly organized and dynamic structure". J Cell Biochem 96 (3): 506–21. doi:10.1002/jcb.20519. PMID 15988757. 
  2. ^ Ris, H. (1961). Ultrastructure and molecular organization of genetic systems. Can. J. Genet. Cytol. 3, 95-120.
  3. ^ Benham C, Mielke S (2005). "DNA mechanics". Annu Rev Biomed Eng 7 (1): 21–53. doi:10.1146/annurev.bioeng.6.062403.132016. PMID 16004565. 
  4. ^ Nelson D, Cox M (2000). Principles of Biochemistry Third Edition. New York: Worth Publishers. pp. 28–39. ISBN 1-57259-153-6. 
  5. ^ Nelson D, Cox M (2000). Principles of Biochemistry Third Edition. New York: Worth Publishers. pp. 38–39. ISBN 1-57259-153-6. 

Wikimedia Foundation. 2010.

Look at other dictionaries:

  • nucleoid — nucleoíd s. n., pl. nucleoízi Trimis de siveco, 10.08.2004. Sursa: Dicţionar ortografic  NUCLEOÍD s.m. (biol.) Nucleul sau echivalentul său la bacterii. [pron. cle o id. / < germ. Nukleoid]. Trimis de LauraGellner, 24.06.2005. Sursa: DN …   Dicționar Român

  • nucleoid — nucleoid. См. нуклеоид. (Источник: «Англо русский толковый словарь генетических терминов». Арефьев В.А., Лисовенко Л.А., Москва: Изд во ВНИРО, 1995 г.) …   Молекулярная биология и генетика. Толковый словарь.

  • Nucleoid — Nucleoid, Kernäquivalent, unscharf abgegrenzter membranloser Bereich in Protocyten, in dem, zusammen mit RNA und Proteinen (Histone fehlen), das ⇒ Bakterienchromosom liegt …   Deutsch wörterbuch der biologie

  • nucleoid — [no͞o′klē oid΄, nyo͞o′klē oid΄] n. a region in the cells of prokaryotes that contains nucleic acids but which is not bounded by a membrane: it is analogous in function to the nucleus of eukaryotic cells …   English World dictionary

  • Nucleoid — Als Kernäquivalent wird der Bereich in einer Bakterienzelle bezeichnet, der von einem in sich geschlossenen DNA Molekül, dem Bakterienchromosom, ausgefüllt wird. Da sich dieser Bereich auch auf elektronenmikroskopischen Abbildungen deutlich vom… …   Deutsch Wikipedia

  • nucleoid — 1. SYN: nucleiform. 2. A nuclear inclusion body. 3. SYN: nucleus (2). [nucleo + G. eidos, resemblance] Lavdovsky n. SYN: astrosphere. * * * nu·cle·oid n(y)ü klē .ȯid adj resembling a nucleus …   Medical dictionary

  • nucleoid — noun Date: 1938 the DNA containing area of a prokaryotic cell (as a bacterium) …   New Collegiate Dictionary

  • nucleoid — (nu kle oid) An irregularly shaped region in the procaryotic cell that contains its genetic material …   Dictionary of microbiology

  • nucleoid — Region of cell in a bacterium that contains the DNA …   Dictionary of molecular biology

  • nucleoid — /nooh klee oyd , nyooh /, Microbiol. n. 1. the central region in a prokaryotic cell, as a bacterium, that contains the chromosomes and that has no surrounding membrane. adj. 2. resembling a nucleus. [1850 55; NUCLE(US) + OID] * * * …   Universalium


Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.