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The Ter-Tus complex is able to stop helicase activity, terminating replication. [125] In eukaryotic cells, termination of replication usually occurs through the collision of the two replicative forks between two active replication origins. The location of the collision varies on the timing of origin firing.
Replication in eukaryotes begins at replication origins, where complexes of initiator proteins bind and unwind the helix. [3] In eukaryotes, it is still unclear what exact combinations of DNA sequence, chromatin structure, and other factors define these sites. The relative contribution of these factors varies between organisms.
The consequences of topological perturbations in DNA are exemplified by DNA replication during which the strands of the duplex are separated; this separation leads to the formation of positive supercoils (DNA overwinding or overtwisting) ahead of the replication fork and intertwining of the daughter strands (precatenanes) behind [10] [19] (Fig. 2).
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.
We also see that the size is another difference between these prokaryotic and eukaryotic cells. The average eukaryotic cell has about 25 times more DNA than a prokaryotic cell does. Replication occurs much faster in prokaryotic cells than in eukaryotic cells; bacteria sometimes only take 40 minutes, while animal cells can take up to 400 hours.
DNA gyrase, or simply gyrase, is an enzyme within the class of topoisomerase and is a subclass of Type II topoisomerases [1] that reduces topological strain in an ATP dependent manner while double-stranded DNA is being unwound by elongating RNA-polymerase [2] or by helicase in front of the progressing replication fork.
The genomes of most eukaryotic mitochondria and plastids are in a single circular chromosome, in line with their bacterial ancestor. However, a good number of eukaryotic species do harbor linear Mitochondrial DNA (mtDNA), some even broken into multiple molecules, across a wide variety of taxa: animals (mammals, medusozoans, sponges), fungi (especially yeast), plants, and Alveolatas.
Gene structure is the organisation of specialised sequence elements within a gene. Genes contain most of the information necessary for living cells to survive and reproduce. [ 1 ] [ 2 ] In most organisms, genes are made of DNA, where the particular DNA sequence determines the function of the gene.