Non-coding DNA
Non-coding DNA sequences are parts of an organism's DNA which do not code for protein sequences. It is often called junk DNA.[2]
Some non-coding DNA is transcribed into functional non-coding RNA molecules (e.g. transfer RNA, ribosomal RNA, and regulatory RNAs). Other DNA sequences are not transcribed, or give rise to RNA transcripts of unknown function. The amount of non-coding DNA varies greatly between species. For example, over 98% of the human genome is noncoding DNA,[3] while only about 2% of a typical bacterial genome is non-coding DNA.
At first, much non-coding DNA had no known biological function. It was called junk DNA, particularly in the press. But many non-coding sequences are functional. These include genes for functional RNA molecules and DNA sequences such as "start replication" signals, centromeres, and telomeres.
Other noncoding sequences have not-yet-discovered functions. This is inferred from the high levels of sequence similarity seen in different species of DNA.
The Encyclopedia of DNA Elements (ENCODE) project[4] suggested in September 2012 that over 80% of DNA in the human genome "serves some purpose, biochemically speaking".[5] This conclusion was strongly criticized by some other scientists.[6][7]
Historical note
The term "junk DNA" was first used by Charles Ehret and Gérard de Haller in a paper.[8] Widely influential was Susuno Ohno's 1972 paper.[9] The term has been replaced by the more neutral term "non-coding DNA".
Non-coding DNA Media
Schematic karyogram of a human, showing an overview of the human genome on G banding, wherein non-coding DNA is present at the centromeres (shown as narrow segment of each chromosome), and also occurs to a greater extent in darker (GC poor) regions.
Mobile genetic elements in the cell (left) and how they can be acquired (right)
References
- ↑ "Worlds record breaking plant: deletes its noncoding "Junk" DNA". Design & Trend. 2013. http://www.designntrend.com/articles/4291/20130512/worlds-record-breaking-plant-deletes-noncoding-junk-dna.htm. Retrieved 2013-06-04.
- ↑ Carey, Nessa 2017. Junk DNA: a journey through the dark matter of the genome. Columbia University Press. ISBN 9780231539418
- ↑ Elgar G. & Vavouri T. 2008. Tuning in to the signals: non-coding sequence conservation in vertebrate genomes. Trends in Genetics. 24 (7): 344–52. [1][dead link]
- ↑ The ENCODE Project Consortium (2012). "An integrated encyclopedia of DNA elements in the human genome". Nature. 489 (7414): 57–74. Bibcode:2012Natur.489...57T. doi:10.1038/nature11247. PMC 3439153. PMID 22955616.
- ↑ Pennisi, E. (2012). "Genomics. ENCODE project writes eulogy for junk DNA". Science. 337 (6099): 1159, 1161. doi:10.1126/science.337.6099.1159. PMID 22955811.
- ↑ Robin McKie (24 February 2013). "Scientists attacked over claim that 'junk DNA' is vital to life". The Observer. http://www.guardian.co.uk/science/2013/feb/24/scientists-attacked-over-junk-dna-claim.
- ↑ Graur, Dan; et al. (2013). "On the immortality of television sets: "function" in the human genome according to the evolution-free gospel of ENCODE". Genome Biology and Evolution. 5 (3): 578–590. doi:10.1093/gbe/evt028. PMC 3622293. PMID 23431001.
- ↑ Ehret C.F. & De Haller G. 1963. Origin, development, and maturation of organelles and organelle systems of the cell surface in Paramecium. Journal of Ultrastructure Research 23: SUPPL6:1–42.
- ↑ Ohno S. 1972. So much junk in our genome. In Brookhaven Symposia in Biology. New York: Gordon & Breach. ed: Smith H.H. 23: p366–370.