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This end stage is known as cellular senescence. The Hayflick limit has been found to correlate with the length of the telomeric region at the end of chromosomes. During the process of DNA replication of a chromosome, small segments of DNA within each telomere are unable to be copied and are lost. [10]
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 replication fork consists of a group of proteins that influence the activity of DNA replication. In order for the replication fork to stall, the cell must possess a certain number of stalled forks and arrest length. The replication fork is specifically paused due to the stalling of helicase and polymerase activity, which are linked together ...
Replication processes permit copying a single DNA double helix into two DNA helices, which are divided into the daughter cells at mitosis. The major enzymatic functions carried out at the replication fork are well conserved from prokaryotes to eukaryotes , but the replication machinery in eukaryotic DNA replication is a much larger complex ...
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.
DNA re-replication (or simply rereplication) is an undesirable and possibly fatal occurrence in eukaryotic cells in which the genome is replicated more than once per cell cycle. [1] Rereplication is believed to lead to genomic instability and has been implicated in the pathologies of a variety of human cancers . [ 2 ]
This stoppage could be permanent or temporary, and could occur in any one of the four cycle phases (G1, S, G2 and M), depending on the status of cells or the activities they are undergoing. [1] During the process, all cell duplication process, including mitosis, meiosis as well as DNA replication, will be paused. [2]
Mitosis occurs only in eukaryotic cells and varies between organisms. [9] For example, animal cells generally undergo an open mitosis, where the nuclear envelope breaks down before the chromosomes separate, whereas fungal cells generally undergo a closed mitosis, where chromosomes divide within an intact cell nucleus.