Origin of replication - wikipedia Origin of replication The origin of replication ( also called the replication origin ) is a particular sequence in a genome at which replication is initiated. This can either involve the replication of DNA in living organisms such as prokaryotes and eukaryotes, or that of DNA or RNA in viruses, such as double - stranded RNA viruses. DNA replication may proceed from this point bidirectionally or unidirectionally. The specific structure of the origin of replication varies somewhat from species to species, but all share some common characteristics such as high AT content ( repeats of adenine and thymine are easier to separate because their base stacking interactions are not as strong as those of guanine and cytosine ). The origin of replication binds the pre-replication complex, a protein complex that recognizes, unwinds, and begins to copy DNA. Contents 1 Types 2 Prokaryotic 2.1 Bacterial genome origins 2.2 Bacterial plasmid origins 3 Eukaryotic 4 Viral 5 See also 6 References 7 External links Types The origin of replication are classified in two ways : Narrow or broad host range High - or low - copy number. There are also significant differences between prokaryotic and eukaryotic origins of replication : Most bacteria have a single circular molecule of DNA, and typically only a single origin of replication per circular chromosome. Most archaea have a single circular molecule of DNA, and several origins of replication along this circular chromosome. Eukaryotes often have multiple origins of replication on each linear chromosome that initiate at different times ( replication timing ), with up to 100,000 present in a single human cell. Having many origins of replication helps to speed the duplication of their ( usually ) much larger store of genetic material. The segment of DNA that is copied starting from each unique replication origin is called a replicon. Origins of replication are typically assigned names containing `` ori ''. Prokaryotic Bacterial genome origins The genome of E. coli consists of a single circular DNA molecule of approximately 4.6 x 10 nucleotide pairs. DNA replication typically begins at a single origin of replication. In E. coli, the origin of replication -- oriC -- consists of three A -- T rich 13 - mer repeats and four 9 - mer repeats. Ten to 20 monomers of the replication initiator protein DnaA bind to the 9 - mer repeats, and the DNA coils around this protein complex forming a protein core. This coiling stimulates the AT rich region in the 13 - mer sequence to unwind, allowing the helicase loader DnaC to load the replicative helicase DnaB to each of the two unwound DNA strands. The helicase DnaB forms the basis of the primosome, a complex of enzymes to which DNA polymerase III is recruited before replication can occur. Bacterial plasmid origins Many bacteria, including E. coli, contain plasmids that each contain an origin of replication. These are separate from the origins of replication that are used by the bacteria to copy their genome and often function very differently. For example, the E. coli plasmid pBR322 uses a protein called Rop / Rom to regulate the number of plasmids that are within each bacterial cell. The most common origin of replication that is used in plasmids for genetic engineering is called pUC. This origin is derived from pBR322 but it contains two mutations. One single point mutation in the origin itself and another that deletes the Rop / Rom gene. This removes all the regulatory constraints on the plasmids replication and the bacteria then go from producing 30 -- 40 plasmids per cell with pBR322 up to producing over 500 with pUC. This allows genetic engineers to produce large quantities of DNA for research purposes. Other origins of replication include pSC101 ( derived from Salmonella, around 5 copies per cell ), 15A origin ( derived from p15A, 10 -- 20 copies per cell ) and Bacterial artificial chromosomes ( 1 copy per cell ). Eukaryotic In eukaryotes, the budding yeast Saccharomyces cerevisiae were first identified by their ability to support the replication of mini-chromosomes or plasmids, giving rise to the name Autonomously replicating sequences or ARS elements. Each budding yeast origin consists of a short ( ~ 11 bp ) essential DNA sequence ( called the ARS consensus sequence or ACS ) that recruits replication proteins. In other eukaryotes, including humans, the base pair sequences at the replication origins vary. Despite this sequence variation, all the origins form a base for assembly of a group of proteins known collectively as the pre-replication complex ( pre-RC ) : First, the origin DNA is bound by the origin recognition complex ( ORC ) which, with help from two further protein factors ( Cdc6 and Cdt1 ), load the mini chromosome maintenance ( or MCM ) protein complex. Once assembled, this complex of proteins indicates that the replication origin is ready for activation. Once the replication origin is activated, the cell 's DNA will be replicated. In metazoans, pre-RC formation is inhibited by the protein geminin, which binds to and inactivates Cdt1. Regulation of replication prevents the DNA from being replicated more than once each cell cycle. In humans an origin of replication has been originally identified near the Lamin B2 gene on chromosome 19 and the ORC binding to it has extensively been studied. Viral Genome of human herpesvirus - 6, a member of the Herpesviridae family. The origin of replication is labeled as `` OOR. '' Viruses often possess a single origin of replication. A variety of proteins have been described as being involved in viral replication. For instance, Polyoma viruses utilize host cell DNA polymerases, which attach to a viral origin of replication if the T antigen is present. See also OriDB the DNA Replication Origin Database Origin of transfer References Jump up ^ Technical Glossary Edward K. Wagner, Martinez Hewlett, David Bloom and David Camerini Basic Virology Third Edition, Blackwell publishing, 2007 ISBN 1 - 4051 - 4715 - 6 Jump up ^ ViralZone : a knowledge resource to understand virus diversity. Hulo C, de Castro E, Masson P, Bougueleret L, Bairoch A, Xenarios I, Le Mercier P. Nucleic Acids Res. 2011 Jan ; 39 ( Database issue ) : D576 - 82. Jump up ^ Martín - Parras L, Hernández P, Martínez - Robles ML, Schvartzman JB ( August 1991 ). `` Unidirectional replication as visualized by two - dimensional agarose gel electrophoresis ''. Journal of Molecular Biology. 220 ( 4 ) : 843 -- 53. PMID 1880800. Jump up ^ http://nar.oxfordjournals.org/content/34/2/564.full Jump up ^ Mott ML, Berger JM ( May 2007 ). `` DNA replication initiation : mechanisms and regulation in bacteria ''. Nature Reviews. Microbiology. 5 ( 5 ) : 343 -- 54. doi : 10.1038 / nrmicro1640. PMID 17435790. Jump up ^ Kelman LM, Kelman Z ( September 2004 ). `` Multiple origins of replication in archaea ''. Trends in Microbiology. 12 ( 9 ) : 399 -- 401. doi : 10.1016 / j. tim. 2004.07. 001. PMID 15337158. Jump up ^ Nasheuer HP, Smith R, Bauerschmidt C, Grosse F, Weisshart K ( 2002 ). `` Initiation of eukaryotic DNA replication : regulation and mechanisms ''. Progress in Nucleic Acid Research and Molecular Biology. 72 : 41 -- 94. doi : 10.1016 / S0079 - 6603 ( 02 ) 72067 - 9. PMID 12206458. Jump up ^ Baker TA, Wickner SH ( 1992 ). `` Genetics and enzymology of DNA replication in Escherichia coli ''. Annual Review of Genetics. 26 : 447 -- 77. doi : 10.1146 / annurev. ge. 26.120192. 002311. PMID 1482121. Jump up ^ oxfordgenetics.com/origins,. Jump up ^ Falaschi A, Giacca M. The quest for a human ori, ' Genetica ', 1994 ; 94 ( 2 - 3 ) : 255 - 66 External links Ori - Finder, an online software for prediction of bacterial and archaeal oriCs Replication Origin at the US National Library of Medicine Medical Subject Headings ( MeSH ) DNA replication ( comparing Prokaryotic to Eukaryotic ) Initiation Prokaryotic ( initiation ) Pre-replication complex dnaC Cdc6 Helicase dnaA dnaB T7 Primase dnaG Eukaryotic ( preparation in G1 phase ) Pre-replication complex Origin recognition complex ORC1 ORC2 ORC3 ORC4 ORC5 ORC6 Cdc6 Cdt1 Minichromosome maintenance MCM2 MCM3 MCM4 MCM5 MCM6 MCM7 Licensing factor Autonomously replicating sequence Single - strand binding protein SSBP2 SSBP3 SSBP4 RNase H RNASEH1 RNASEH2A Helicase : HFM1 Primase : PRIM1 PRIM2 Both Origin of replication / Ori / Replicon Replication fork Lagging and leading strands Okazaki fragments Primer Replication Prokaryotic ( elongation ) DNA polymerase III holoenzyme dnaC dnaE dnaH dnaN dnaQ dnaT dnaX holA holB holC holD holE Replisome DNA ligase DNA clamp Topoisomerase DNA gyrase Prokaryotic DNA polymerase : DNA polymerase I Klenow fragment Eukaryotic ( synthesis in S phase ) Replication factor C RFC1 Flap endonuclease FEN1 Topoisomerase Replication protein A RPA1 Eukaryotic DNA polymerase : alpha POLA1 POLA2 PRIM1 PRIM2 delta POLD1 POLD2 POLD3 POLD4 epsilon POLE POLE2 POLE3 POLE4 DNA clamp PCNA Control of chromosome duplication Both Movement : Processivity DNA ligase Termination Telomere : Telomerase TERT TERC DKC1 Retrieved from `` https://en.wikipedia.org/w/index.php?title=Origin_of_replication&oldid=810778824 '' Categories : DNA replication Hidden categories : All articles with unsourced statements Articles with unsourced statements from February 2016 Articles with unsourced statements from December 2013 Talk Contents About Wikipedia Čeština Deutsch Español فارسی Français Galego Italiano Nederlands Polski Português Русский Српски / srpski Srpskohrvatski / српскохрватски Svenska Türkçe 中文 Edit links This page was last edited on 17 November 2017, at 11 : 11. Text is available under the Creative Commons Attribution - ShareAlike License ; additional terms may apply. By using this site, you agree to the Terms of Use and Privacy Policy. Wikipedia ® is a registered trademark of the Wikimedia Foundation, Inc., a non-profit organization. About Wikipedia

Question: where does dna replication begin on a chromosome
Answer: bidirectionally or unidirectionally