6: Telomeres & Telomerase

Part 6

What is the end-replication problem?

DNA cannot fully replicate the ends of linear chromosomes.

What are telomeres, and why are they composed of repetitive DNA?

• Telomeres are specialized, protective caps found at the ends of linear eukaryotic chromosomes

• acts as a buffer that prevents the loss of genetic information during DNA replication & protects chromosomes from being recognized as damaged DNA

• repetitive DNA sequences that protect chromosome ends (helps the problem of “end replication”)

How does the enzyme telomerase extend telomeres?

Extends telomeres by using the RNA template.

Why do most somatic cells show telomere shortening over time?

They lack sufficient active telomerase enzyme to counteract the "end replication problem," where DNA polymerase cannot fully replicate the very ends of linear chromosomes during division.

• somatic cells lack sufficient telomerase enzyme to repair these ends, telomeres progressively shorten, acting as a "mitotic clock" that eventually triggers cell senescence