Telomeres and Telomerase

Introduction

• Telomeres are repetitive DNA sequences at the ends of eukaryotic chromosomes.
• They act as protective "caps" to prevent chromosome degradation.
• Composed of TTAGGG repeats, found in humans and other organisms.

The End-Replication Problem

• Eukaryotic chromosomes are linear, unlike circular bacterial chromosomes.
• The ends pose a replication issue: not fully copied in each cell division, leading to gradual shortening.
• Leading Strand: synthesized continuously.
• Lagging Strand: synthesized in Okazaki fragments, initiating with RNA primers.
• Final RNA primer on lagging strand cannot be replaced, causing a gap.

Telomeres

• Serve as buffers to protect chromosome ends and genes during replication.
• Telomeres shorten gradually over divisions, connected to cellular aging.
• Shortened telomeres can trigger DNA repair mechanisms, causing problems.

Telomerase

• An enzyme that can extend telomeres, preventing their shortening.
• RNA-dependent DNA polymerase using RNA template to add nucleotides.
• Active in germ cells and some stem cells, but usually not in somatic cells.
• Many cancer cells reactivate telomerase, aiding in unchecked growth.

Implications of Telomere Shortening

• Progressive telomere shortening is linked to aging and limited cell division.
• Telomerase activity may counteract aging effects and is a focus in cancer therapy.

References

• Articles and studies from various sources supporting telomere and telomerase information.
• Attribution given to Khan Academy and other scientific publications.

Visual Aids

• Diagrams and images illustrating DNA replication and telomerase function.

These notes cover the basics of telomeres and telomerase, providing insight into their roles in DNA replication, cellular aging, and their connection to diseases such as cancer.