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Human chromosomes (grey) capped by telomeres (white). A telomere (/ ˈ t ɛ l ə m ɪər, ˈ t iː l ə-/; from Ancient Greek τέλος (télos) 'end' and μέρος (méros) 'part') is a region of repetitive nucleotide sequences associated with specialized proteins at the ends of linear chromosomes (see Sequences).
As telomeres shorten as a natural consequence of repeated cell division or due to other factors, such as oxidative stress, [19] shelterin proteins lose the ability to bind to telomeric DNA. When telomeres reach a critically short length, sufficient shelterin proteins to inhibit checkpoint activation are not available, although NHEJ and HR ...
The presence of repeated sequence DNA makes it easier for areas of homology to align, thereby controlling when and where recombination occurs. In addition to playing an important role in recombination, tandem repeats also play important structural roles in the genome. For example, telomeres are composed mainly of tandem TTAGGG repeats. [15]
Although the replication and transcription of DNA is highly standardized in eukaryotes, the same cannot be said for their karyotypes, which are highly variable. There is variation between species in chromosome number, and in detailed organization, despite their construction from the same macromolecules .
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.
Telomeres are specialized protein–DNA constructs present at the ends of eukaryotic chromosomes, which prevent them from degradation and end-to-end chromosomal fusion. Most vertebrate telomeric DNA consists of long (T T A G G G)n repeats of variable length, often around 3-20kb. Subtelomeres are segments of DNA between telomeric caps and ...
Telomeres are long stretches of repetitive sequences that cap the ends of the linear chromosomes and prevent degradation of coding and regulatory regions during DNA replication. The length of the telomeres decreases each time the genome is replicated and has been implicated in the aging process. [54]
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.