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20-September-2008 09:29:09 - Complementary DNA For the general property of complementarity in molecular biology, see Complementarity molecular biology. For complementation tests used in genetics research, see Complementation genetics. Output from a cDNA microarray used in testing 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.1 cDNA is often used to clone eukaryotic genes in prokaryotes. 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. Contents 1 Overview 2 Synthesis 3 Applications 4 Viruses 5 References 6 External links Overview The central dogma of molecular biology outlines that in synthesizing proteins, DNA is transcribed into mRNA, which is translated into protein. One difference between eukaryotic and prokaryotic genes is that eukaryotic genes can contain introns intervening sequences, which are not coding sequences, and must be 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. 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 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 pairs 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 processes the pre-mRNA strands by splicing out introns, and adding a poly-A tail and 5' Methyl-Guanine cap. This mixture of mature mRNA strands are extracted from the cell. A poly-T oligonucleotide primer is hybridized onto the 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 gene cloning or as gene probes or in the creation of a cDNA library. Partial sequences of cDNAs are often obtained as expressed sequence tags. 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 ^ cDNA - Definitions from Dictionary.com. dictionary.reference.com. Retrieved on 2008-04-26. External links H-Invitational Database Functional Annotation of the Mouse database v d e Types of nucleic acids Constituents Nucleobases | Nucleosides | Nucleotides | Deoxynucleotides Ribonucleic acids RNA | mRNA pre-mRNA/hnRNA | tRNA | rRNA | aRNA | gRNA | miRNA | ncRNA | piRNA | shRNA | siRNA | snRNA | snoRNA | stRNA | ta-siRNA | tmRNA Deoxyribonucleic acids DNA | cDNA | gDNA | msDNA | mtDNA Nucleic acid analogues GNA | LNA | PNA | TNA | morpholino Cloning vectors phagemid | plasmid | lambda phage | cosmid | P1 phage | fosmid | BAC | YAC | HAC Major families of biochemicals Saccharides | Carbohydrates | Glycosides | | Amino acids | Peptides | Proteins | Glycoproteins | | Lipids | Terpenes | Steroids | Carotenoids Alkaloids | Nucleobases | Nucleic acids | | Enzyme cofactors | Flavonoids | Polyketides | Tetrapyrroles Retrieved from http://en..org/wiki/Complementary_DNA Categories: DNA Views Article Discussion this page History Personal tools Log in / create account Navigation Main page Contents Featured content Current events Random article Search Go Search Interaction Community portal Recent changes Contact Donate to Help Toolbox What links here Related changes Upload file Special pages Printable version Permanent link Cite this page Languages العربية Català Deutsch Español Ù?ارسی Français Bahasa Indonesia Italiano עברית Nederlands 日本語 Polski Suomi Svenska УкраїнÑ?ька اردو ä¸æ–‡ This page was last modified on 29 July 2008, at 20:15
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