Complementary DNA 7330 222876033 2008-07-01T15:20:59Z 169.226.137.240 /* Synthesis */ {{for|the general property of complementarity in molecular biology|Complementarity (molecular biology)}} {{for|complementation tests used in genetics research|Complementation (genetics)}} [[Image:Cdnaarray.jpg|thumb|right|250px|Output from a '''cDNA''' [[microarray]] used in testing]] In [[genetics]], '''complementary DNA''' ('''cDNA''') is [[DNA]] synthesized from a mature [[mRNA]] template in a reaction catalyzed by the enzyme [[reverse transcriptase]].<ref> {{cite web |url=http://dictionary.reference.com/browse/cDNA |title=cDNA - Definitions from Dictionary.com |publisher=dictionary.reference.com |accessdate=2008-04-26 |last= |first= }} </ref> cDNA is often used to clone [[eukaryote|eukaryotic]] [[gene]]s in [[prokaryote]]s. cDNA is also produced by [[retroviruses]] (such as [[HIV-1]], [[HIV-2]], [[Simian Immunodeficiency Virus]], etc.) which is integrated into its host to create a [[provirus]]. == Overview == The [[central dogma of molecular biology]] outlines that in synthesizing [[protein]]s, [[DNA]] is [[transcription (genetics)|transcribed]] into [[mRNA]], which is [[translation (genetics)|translated]] into protein. One difference between eukaryotic and prokaryotic genes is that eukaryotic genes can contain [[intron]]s (intervening sequences), which are not coding sequences, and must be [[splicing|spliced]] out of the RNA primary transcript before it becomes mRNA and can be translated into protein. Prokaryotic genes have no introns, so their RNA is not subject to [[splicing (genetics)|splicing]]. Often it is desirable to express eukaryotic genes in prokaryotic cells. A simplified method of doing so would include the addition of eukaryotic DNA to a prokaryotic host, which would transcribe the DNA to mRNA and then translate it to protein. However, as eukaryotic DNA has introns, and since prokaryotes lack the machinery to splice them, the splicing of eukaryotic DNA must be done prior to adding the eukaryotic DNA into the host. This DNA which was made as a complementary to the RNA is called complementary DNA (cDNA). To obtain [[gene expression|expression]] of the protein encoded by the eukaryotic cDNA, prokaryotic regulatory sequences would also be required (e.g. a [[promoter]]). == Synthesis == Though there are several methods for doing so, cDNA is most often synthesized from mature (fully spliced) mRNA using the enzyme [[reverse transcriptase]]. This enzyme operates on a single strand of mRNA, generating its complementary DNA based on the pairing of RNA [[base pair]]s (A, U, G and C) to their DNA complements (T, A, C and G respectively). To obtain eukaryotic cDNA whose introns have been spliced: # A eukaryotic cell transcribes the DNA (from genes) into RNA ([[pre-mRNA]]). # The same cell [[Post-transcriptional modification|processes]] the pre-mRNA strands by splicing out introns, and adding a [[Polyadenylation|poly-A tail]] and [[5' cap|5’ Methyl-Guanine cap]]. # This mixture of mature mRNA strands are extracted from the cell. # A poly-[[thymine|T]] [[oligonucleotide]] [[primer]] is hybridized onto the [[Polyadenylation|poly-A tail]] of the mature mRNA template, or random hexamer primers can be added which contain every possible 6 base single strand of DNA and can therefore hybridize anywhere on the RNA (Reverse transcriptase requires this double-stranded segment as a primer to start its operation.) # Reverse transcriptase is added, along with deoxynucleotide triphosphates (A, T, G, C). The reverse transcriptase scans the mature mRNA and synthesizes a sequence of DNA that complements the mRNA template. This strand of DNA is complementary DNA. Note that the [[central dogma of molecular biology]] is not broken in this process. == Applications == Complementary DNA is often used in [[clone (genetics)|gene cloning]] or as [[gene probe]]s or in the creation of a [[cDNA library]]. Partial sequences of cDNAs are often obtained as [[expressed sequence tag]]s. == Viruses == Some viruses also use cDNA to turn their viral RNA into mRNA (viral RNA → cDNA → mRNA). The mRNA is used to make viral proteins to take over the host cell. == References == {{reflist}} == External links == * [http://www.h-invitational.jp/ H-Invitational Database] * [http://fantom.gsc.riken.jp/ Functional Annotation of the Mouse database] {{Nucleic acids}} [[Category:DNA]] [[ar:دنا متمم]] [[ca:ADN complementari]] [[de:CDNA]] [[es:ADN complementario]] [[fr:ADN complémentaire]] [[id:DNA komplemen]] [[it:DNA complementare]] [[he:CDNA]] [[nl:CDNA]] [[ja:相補的DNA]] [[pl:CDNA]] [[fi:CDNA]] [[sv:CDNA]] [[uk:Комплементарна ДНК]] [[ur:متمم دنا]] [[zh:互補DNA]]