Summary
Shortening of chromosome end caps with each division eventually triggers permanent growth arrest called senescence.
In depth
Telomeres are repeats (TTAGGG in humans) at chromosome ends that protect against degradation and fusion. DNA polymerase cannot fully copy the lagging strand end, so telomeres shorten by 50 to 100 bases per division, the end-replication problem.
After about 50 divisions (the Hayflick limit) cells stop dividing. Stem and cancer cells express telomerase to avoid this.
Telomerase is a ribonucleoprotein with a built-in RNA template that adds TTAGGG repeats, and it is active in germ cells, many stem cells and about 85 to 90 percent of cancers; the rest use a recombination route called ALT. Shelterin proteins cap the ends and prevent them from being recognised as broken DNA. Elizabeth Blackburn, Carol Greider and Jack Szostak received the 2009 Nobel Prize for this work.
Short telomeres trigger a p53-dependent stop, which acts as a tumour-suppressing mechanism but also contributes to tissue ageing. Dyskeratosis congenita, caused by telomerase defects, leads to bone marrow failure. Senescent cells secrete inflammatory molecules (the SASP) that affect neighbouring tissue, and drugs that remove them (senolytics) are under study.
Remember: telomere length is a marker, not a clock that sets lifespan alone; lifestyle, genetics and damage all contribute.
Frequently asked questions
What is Telomeres and Senescence?
Shortening of chromosome end caps with each division eventually triggers permanent growth arrest called senescence.
Which area of biology covers Telomeres and Senescence, and how advanced is it?
Telomeres and Senescence is one of the 52 topics in Cell Biology. It is rated Advanced, so it suits learners who want specialist depth. Related topics in this area include Cell Cycle Checkpoints, Cancer Cell Biology, Cyclin-Dependent Kinases.
Why does Telomeres and Senescence matter?
Short telomeres are linked to ageing-related diseases, while telomerase reactivation is a feature of about 90 percent of cancers.
What should I learn before Telomeres and Senescence?
Work through the Beginner topics in Cell Biology first, such as Cell Theory, Prokaryotic Cell, Eukaryotic Cell, then return to Telomeres and Senescence. Advanced topics assume the Intermediate vocabulary.
What topics are related to Telomeres and Senescence?
The closest topics to Telomeres and Senescence are Cell Cycle Checkpoints, Cancer Cell Biology, Cyclin-Dependent Kinases, Receptor Tyrosine Kinases. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Telomeres and Senescence?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Telomeres and Senescence. To practise the whole of Cell Biology, use the Cell Biology quiz.
How is Telomeres and Senescence different from Cell Cycle Checkpoints?
Telomeres and Senescence: Shortening of chromosome end caps with each division eventually triggers permanent growth arrest called senescence. Cell Cycle Checkpoints: Control points at G1/S, G2/M and metaphase that halt the cycle until DNA and spindle attachments are correct. Read both side by side and note what each one explains.
How should I study Telomeres and Senescence step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Cell Cycle Checkpoints and explain the difference aloud. Finally, take the Cell Biology quiz and come back to this page for any question you miss.