Rucete ✏ Biology In a Nutshell
1. What Are Telomeres?
- Telomeres are repetitive DNA sequences (e.g., TTAGGG in humans) found at the ends of linear chromosomes.
- They protect genetic information by preventing the ends from deteriorating or fusing with other chromosomes.
2. The End Replication Problem
- During DNA replication, the lagging strand cannot be fully replicated at the very end.
- This happens because primase cannot add an RNA primer at the extreme 3' end after the last Okazaki fragment.
- As a result, the new strand is shorter than the original, leading to gradual shortening of chromosomes after each cell division.
3. Role of Telomerase
- Telomerase is an enzyme that adds telomeric repeats to the 3' end of the template strand, using its own RNA template.
- This allows DNA polymerase to complete replication of the lagging strand.
- Active in germ cells, stem cells, and cancer cells, but mostly inactive in somatic cells, leading to aging-related telomere shortening.
4. Biological Significance
- Shortened telomeres are associated with cell aging and replicative senescence.
- Telomerase activity is linked to cell immortality in cancer, making it a target for cancer research.
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Biology in a nutshell