Replicons, multiple

Compared with the process in bacteria, replication of DNA of a human cell requires multiple origins of replication, each of which leads to copying of replicons, regions 30 to 300 kilobase pairs in size. 

Aiyar, A., Tyree, C. and Sugden, B. (1998) The plasmid replicon of EBV consists of multiple as-acting elements that facilitate DNA synthesis by the cell and a viral maintenance element. EMBO J., 17, 6394-6403. 

Multiple replicons In eukaryotes, replication of chromosomal DNA occurs only in the S phase of the cell cycle. As for bacterial DNA (see Topic F3), eukaryotic DNA is replicated semi-conservatively. Replication of each linear DNA molecule in a chromosome starts at many origins, one every 3-300 kb of DNA depending on the species and tissue, and proceeds bi-directionally from each origin. The use of multiple... 

Multiple Replicon Model of Eukaryotic Chromosomal DNA Replication. 

Consequently, approximately one month is required for this DNA replication. Eukaryotic DNA synthesis is significantly faster than expected because each chromosome contains multiple replication units (replicons). 

In contrast to bacterial chromosomes (see section LA. of this chapter), eukaryotic chromosomes have multiple points of origin at which replication begins. Bubbles appear at these points on the chromosomes. At each end of a bubble, a replication fork forms thus, each bubble has two forks. DNA synthesis occurs at each of these forks, as illustrated in Figure 13.8. As the bubbles enlarge, they eventually merge, and replication is completed. Because eukaryotic chromosomes contain multiple points of origin of replication (and, thus, multiple replicons-units of replication), duplication of such large chromosomes can occur within a few hours. 

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