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Telomerase is a reverse transcriptase enzyme that carries its own RNA molecule (e.g., with the sequence 3′-CCCAAUCCC-5′ in Trypanosoma brucei) [3] which is used as a template when it elongates telomeres. Telomerase is active in gametes and most cancer cells, but is normally absent in most somatic cells.
During DNA replication, DNA polymerase cannot replicate the sequences present at the 3' ends of the parent strands. This is a consequence of its unidirectional mode of DNA synthesis: it can only attach new nucleotides to an existing 3'-end (that is, synthesis progresses 5'-3') and thus it requires a primer to initiate replication.
The two major protein complexes that bind to telomeric DNA in S. cerevisiae are: [citation needed] the Cdc13-Stn1-Ten1 (CST) complex, which binds the single-stranded DNA (ssDNA) of the 3' G-rich overhang at the end of the telomere, and; the Rif1-Rif2-Rap1 complex, which binds the double-stranded DNA (dsDNA) preceding the 3' overhang.
[10] [11] Examining telomeres is one of the most important fields of research related to aging. It is also very important to investigate the mechanisms of maintaining telomerase, cell cleansing (old cells that accumulate in tissues and sometimes cause cancer and inflammation) and the production of new cells in long-lived organisms.
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.
During DNA replication, the replisome will unwind the parental duplex DNA into a two single-stranded DNA template replication fork in a 5' to 3' direction. The leading strand is the template strand that is being replicated in the same direction as the movement of the replication fork.
Knockout of subtelomeres in Schizosaccharomyces pombe cells after the loss of telomerase does not affect cell survival, indicating that subtelomeres are not necessary for cell survival. [20] An explanation as to why subtelomeres are not necessary after the loss of telomerase is because the chromosomes can use intra or inter-chromosomal ...
Recombination is important as a source of genetic diversity, as a mechanism for repairing damaged DNA, and a necessary step in the appropriate segregation of chromosomes in meiosis. [14] The presence of repeated sequence DNA makes it easier for areas of homology to align, thereby controlling when and where recombination occurs.