Non-coding DNA
Non-coding DNA sequences are those parts of an organism's DNA that 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), while others are not transcribed or give rise to RNA transcripts of unknown function. The amount of non-coding DNA varies greatly among 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]
References
- ↑ "Worlds record breaking plant: deletes its noncoding "Junk" DNA". Design & Trend. 2013. 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]
- ↑ 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.
- ↑ 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. doi:10.1093/gbe/evt028. PMC 3622293. PMID 23431001.