Question

the end of the telomere can't be replicated. Why is that?

Answer 1

This is an issue called the "end-replication issue". This depends on generally understanding that while DNA is bidirectional (every integral strand has a 5' to 3' arrangement), the DNA polymerase that duplicates the little girl strands is unidirectional (incorporating just from the 5' to 3' end).

Accordingly, little girl strand combination happens distinctively between the 3'- 5' mother and the 5'- 3' mother. The 3'- 5' mother is known as the main strand, and a RNA preliminary can strengthen to the 3' end of the mother, and take into consideration DNA polymerase to reproduce from the groundwork to the very end (since the little girl will keep running from the 5'- 3' toward the DNA polymerase).

In any case, the 5'- 3' mother is tricky. This strand is the slacking strand, in which various RNA preliminaries must be utilized to make spasmodic 'Okazaki parts" of DNA as helicase unfastens the mother twofold helix. Typically the RNA preliminaries are supplanted and filled in with DNA polymerase and ligated upon finish unfastening. Be that as it may, the last RNA introduction on the 3' end of the mother strand can't be filled in with DNA, and the RNA preliminary is debased.

Accordingly, as DNA is reproduced again and again, around 50-200bp of DNA is unreplicated at the mother 3' end. Since the closures are topped with telomeres, telomere shortening unavoidably happens.

In principle, telomerase can act to 'fill-in' this hole by topping the unreplicated end with new telomeres. In any case, telomerase movement isn't communicated by most substantial cells, and essentially works in germ and some embryonic cells.

As we as a whole know, with a straight chromosome, on the slacking strand (layout 5'- >3') of DNA replication, when the last bit of RNA groundwork at the 3' end is evacuated, the DNA can't be expanded and this makes the end replication issue

The replication birthplace is probably not going to be at the very end of the chromosome. Along these lines, the finish of the main strand is well on the way to be secured, which leaves the slacking strand to be the main issue, in a perfect world.