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Furthermore, it was predicted that a specialized DNA polymerase (originally called a tandem-DNA-polymerase) could extend telomeres in immortal tissues such as germ line, cancer cells and stem cells. It also followed from this hypothesis that organisms with circular genome, such as bacteria, do not have the end replication problem and therefore ...
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 ...
Therefore, TERRA expression may play an important role in the proper orchestration of DNA replication, as TERRA may hybridize with single-stranded DNA during replication. [ 21 ] [ 26 ] [ 27 ] [ 28 ] In cells with long telomeres and high TERRA expression, this could potentially lead to replicative arrest and the eventual collapse of the ...
Shelterin (also called telosome) is a protein complex known to protect telomeres in many eukaryotes from DNA repair mechanisms, as well as to regulate telomerase activity. In mammals and other vertebrates, telomeric DNA consists of repeating double-stranded 5'-TTAGGG-3' (G-strand) sequences (2-15 kilobases in humans) along with the 3'-AATCCC-5' (C-strand) complement, ending with a 50-400 ...
When the cell does this due to telomere-shortening, the ends of different chromosomes can be attached to each other. This solves the problem of lacking telomeres, but during cell division anaphase, the fused chromosomes are randomly ripped apart, causing many mutations and chromosomal abnormalities. As this process continues, the cell's genome ...
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.
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 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.