Telomeres are repetitive nucleotide sequences located at the ends of chromosomes that protect the ends from deterioration or fusion with other chromosomes. They shorten each time a cell divides until a length is reached that triggers cell senescence or death. The enzyme telomerase maintains telomere length by adding telomeric repeats to chromosome ends using its own RNA component as a template. Telomerase is active in germ cells, stem cells, and cancer cells, allowing indefinite cell division, but not in most somatic cells, limiting their replicative lifespan.

1. KASHMEERA.N.A
III SEM MSc ZOOLOGY
ROLL NO : 37
CHRIST COLLEGE

3. WHAT ARE TELOMERES ?

4. Telomeres are the ends of chromosomes

5. • Telomeres are repetitive nucleotide sequences
located at the termini of linear chromosomes
of most eukaryotic organisms.
• Its name is derived from the Greek nouns
telos ='end' and merοs = 'part’.
• Most prokaryotes do not have telomeres.

6. TELOMERES
Repetitive DNA sequence
(TTAGGG in vertebrates)
Specialized proteins
Form a 'capped' end structure

7. • Telomere specific proteins, eg. TRF1 & TRF2
bind to the repeat sequence and protect the
ends.
• Without these proteins, telomeres are acted
upon by DNA repair pathways leading to
chromosomal fusions.

8. • While replicating DNA, the eukaryotic DNA
replication enzymes cannot replicate the
sequences present at the ends of the
chromosomes .
• Hence, these sequences and the information
they carry may get lost.
• Telomeres "cap" the end-sequences and
themselves get lost in the process of DNA
replication.

9. Telomeres are the ends of
chromosomes
 Protect ends
 Maintain length

10. THE END REPLICATION PROBLEM
RNA primer near
end of the
chromosome on
lagging strand can’t
be replaced with
DNA since DNA
polymerase must
add to a primer
sequence.

12. TELOMERASE
• Telomeric sequence is maintained by a special
enzyme called telomerase.
• Specialized reverse transcriptase.
• Carries its own template RNA , which is
complementary to telomeric repeat sequences.

13. Telomerase "replenishes" the telomere "cap" of the DNA

14. • In most multicellular eukaryotic organisms,
telomerase is active only in germ cells,
stem cells, and certain white blood cells.

15. HOW TELOMERASE WORK ?

16. MECHANISM OF TELOMERASE ACTION
Tetrahymena
Model organism used in telomere & telomerase research.

17. MECHANISM OF TELOMERASE ACTION

18. Removal of the RNA
primer leaves an overhanging 3' end of
chromosomal DNA, which can
form loops at the ends of eukaryotic
chromosomes

19. CLINICAL ASPECTS

20. •Many experiments have
shown that there is a direct
relationship between
telomeres and aging, and that
telomerase has the ability to
prolong life and cell division.

21. • Most somatic cells do not have sufficiently
high levels of telomerase to maintain the
length of their telomeres for an indefinite
number of cell divisions.
• Consequently, telomeres gradually shorten as
cells age.
• This shortening eventually leads to cell death
or senescence.

22. • Cancer cells express abnormally high levels of
telomerase, allowing them to continue dividing
indefinitely.