elect the best description of the end-replication problem. Telomere extension ca
ID: 140500 • Letter: E
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elect the best description of the end-replication problem. Telomere extension cannot occur when telomeres have been shortened by rounds of replication. When replicating linear DNA, the end primer cannot be replaced because of a oWhen replicating completely around circular DNA, the end primer must be incorporated into the DNA Replication near chromosome ends is significantly slower because of a lack of replication origins. When replicating circular DNA, winding of the helix can stall the completion of replication until unwound.Explanation / Answer
The best description for end replication problem is when replicating linear DNA, the end primer cannot be replaced because of a lack of adjacent 3'OH.
The requirement for an RNA primer to intiate all new DNA synthesis creates a dilemma for the replication of the ends of linear chromosomes. This is called the end replication problem. In this case a single internal RNA primer can direct the intiation of a DNA strand that can be extended to the extreme 5' terminus of its template.
Cells solves th end replication problem in different ways. One solution is to used a protein instead of an RNA as the primer for the last Okazaki fragment at each end of chromosome. In this case, the "priming protein" binds to the lagging strand template and uses amino acid to provide an OH that replaces the 3'OH normally provided by an RNA primer. By priming the last lagging strand, the priming protein becomes covalently linked to the 5' end of the chromsome. Terminally attached replication proteins of this kind are found at the end of the linear chroomsomes of certain species of bacteria (circular chromosomes) and at the ends of the linear chromosomes of certain bacterial and animal viruses.In eukaryotes chromosomes ends are called telomeres which have head to tail repeats. they are mostly double stranded , the 3' end of each chromosome extends beyond the 5' and as single standed DNA. So, the origin recruits specialized DNA polymerase called telomerase.Like all ither DNA polymerases , telomerases acts as extend the 3' end of its DNA substrate. The RNA component of telomerase serves as template for adding the telomeric sequence to the 3' terminus at the end of the chromosome. Telomerase specially elongates the 3'OH of particular single strande DNA sequences using its own RNA as a template. The newly synthesized DNA is single stranded.
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