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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 ...
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]
As telomeres do not contain a canonical stop codon signaling the end of RNA transcription, it remains unclear exactly where transcription ceases along the telomere tracks. Similarly to most mRNAs transcribed in the nucleus, nearly all TERRA transcripts contain a 7-methylguanosine (m 7 G) cap structure at their 5' end. [ 10 ]
(A) Telomere-bound proteins involved in preventing the activation of the DNA damage response checkpoint and of DSB repair mechanisms in S. cerevisiae (top) and in humans (bottom). (B) Overview of the normal function of telomere-shelterin complexes and the pathways activated by telomere shortening. [5]
In DNA replication, DNA-dependent DNA polymerases make copies of DNA polynucleotide chains. To preserve biological information, it is essential that the sequence of bases in each copy are precisely complementary to the sequence of bases in the template strand. Many DNA polymerases have a proofreading activity. Here, the polymerase recognizes ...
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]
The process of duplicating DNA is called DNA replication, and it takes place by first unwinding the duplex DNA molecule, starting at many locations called DNA replication origins, followed by an unzipping process that unwinds the DNA as it is being copied. However, replication does not start at all the different origins at once.
The initiator is the protein that recognizes the replicator and activates replication initiation. [1] Sometimes in bacteriology, the term "replicon" is only used to refer to chromosomes containing a single origin of replication and therefore excludes the genomes of archaea and eukaryotes which can have several origins. [2]