Question

(Molecular Biology) Explain how telomerase extends telomeres.

Answer 1

Answer :

Enzyme telomerase can be used to extend telomeres.

Telomeres: Repetitive regions at the very ends of the chromosomes are called telomeres. Telomeres act as caps that protect the internal region of the chromosomes and they are worn down by a small amount in each round of DNA replication.Telomeres need to be protected from a cell's DNA repair system because they have single-stranded overhangs.The overhangs at the lagging strand end of the chromosome is due to incomplete end replication. Telomere shortening has been connected to aging of cells and due to which cells can only divide a certain number of times.

Telomerase: Some cells have the ability to reverse telomere shortening by expressing telomerase, an enzyme that extends the telomeres of chromosomes. Telomerase is an RNA dependent DNA polymerase (enzyme that can make DNA using RNA as a template).

Process:Telomerase binds to a special RNA molecule that contains a sequence complementary to the telomeric repeat. It repeats i.e. adds nucleotides to the overhanging strand of the telomere DNA using the complementary RNA as a template. When the overhang is long enough, a matching strand can be made by the normal DNA replication machinery (using RNA primer and DNA polymerase) producing double-stranded DNA.The primer may not be positioned right at the chromosome end and cannot be replaced with DNA, so an overhang will still be present and the overall length of the telomere will be greater.

Potential use: Many cancer cells have shortened telomeres and telomerase is active in these cells.If telomerase could be inhibited by drugs as part of cancer therapy, their excess division / growth of cancerous tumor could be stopped.