Telomeres

Why do eukaryotic DNA molecules get shorter during replication?

Because after replication, each new strand has a gap at the 5’ end where the RNA primer was removed, leaving part of the template un-replicated and causing DNA to shorten each division.

What are telomeres and what is their function?

Are protective DNA caps made of many repeats of TTAGGG at chromosome ends. They prevent genes from being shortened during DNA replication.

How do telomeres help protect genes?

Telomeres contain repeated, non-gene sequences, so even as they shorten, actual genes are not lost.

How do cells use telomere shortening?

Telomere shortening acts as a cell “age counter.” After about 50 divisions, telomeres become too short and the cell dies.

What is telomerase and what does it do?

Is an enzyme that adds DNA to telomeres, lengthening them so cells (like bone marrow stem cells and gamete-producing cells) can divide many more times.