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Eukaryotes initiate DNA replication at multiple points in the chromosome, so replication forks meet and terminate at many points in the chromosome. Because eukaryotes have linear chromosomes, DNA replication is unable to reach the very end of the chromosomes. Due to this problem, DNA is lost in each replication cycle from the end of the chromosome.
The temporal order of replication of all the segments in the genome, called its replication-timing program, can now be easily measured in two different ways. [1] One way simply measures the amount of the different DNA sequences along the length of the chromosome per cell.
The eukaryotic cell cycle consists of four distinct phases: G 1 phase, S phase (synthesis), G 2 phase (collectively known as interphase) and M phase (mitosis and cytokinesis). M phase is itself composed of two tightly coupled processes: mitosis, in which the cell's nucleus divides, and cytokinesis, in which the cell's cytoplasm and cell membrane divides forming two daughter cells.
Studies in Xenopus revealed the Mcm2-7 complex is a critical component of DNA replication machinery. [6] Inactivation of temperature sensitive mutants of any of the Mcm proteins in "S. cerevisiae" caused DNA replication to halt if inactivation occurred during S phase, and prevented initiation of replication if inactivation occurred earlier. [6]
The process of semiconservative replication for the site of DNA replication is a fork-like DNA structure, the replication fork, where the DNA helix is open, or unwound, exposing unpaired DNA nucleotides for recognition and base pairing for the incorporation of free nucleotides into double-stranded DNA.
A licensing factor is a protein or complex of proteins that allows an origin of replication to begin DNA replication at that site. Licensing factors primarily occur in eukaryotic cells, since bacteria use simpler systems to initiate replication. However, many archaea use homologues of eukaryotic licensing factors to initiate replication. [1]
As a summary, a typical DNA rolling circle replication has five steps: [2] Circular dsDNA will be "nicked". The 3' end is elongated using "unnicked" DNA as leading strand (template); 5' end is displaced. Displaced DNA is a lagging strand and is made double stranded via a series of Okazaki fragments. Replication of both "unnicked" and displaced ...
In prokaryotes, DnaA hydrolyzes ATP in order to unwind DNA at the oriC. This denatured region is accessible to the DnaB helicase and DnaC helicase loader. Single-strand binding proteins stabilize the newly formed replication bubble and interact with the DnaG primase. DnaG recruits the replicative DNA polymerase III, and replication begins.