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BY - TAKSHITA SHARMA (68) And special thanks to Ekatri Gupta

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Repetitive DNA sequences at the ends of all human chromosomes.

In humans there are 46 chromosomes and thus 92 telomeres ( one at each end).

They contain thousands of repeats of the six- nucleotide sequence , TTAGGG.

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THEY STOP CHROMOSOMES FROM LOSING BASE PAIR SEQUENCES AT THEIR ENDS

WITHOUT TELOMERES, THE ENDS OF THE CHROMOSOMES WOULD BE “REPAIRED” , LEADING TO CHROMOSOMES FUSION AND MASSIVE GENOMIC INSTABILITY

THEY SEP A RATE ONE CHROMOSOME FROM ANOTHER IN THE DNA SEQUENCE.

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Telomeres are also thought to be the clock that regulates how many times an individual cell can divide.   Telomeric sequences shorten each time the DNA replicates

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Once the telomere shrinks to a certain level, the cell can no longer divide . Its metabolism slows down, it ages, and dies. Healthy human cells are mortal because they can divide only a finite number of times, growing older each time they divide. Thus cells in an elderly person are much older than cells in an infant

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Telomerase (TEE-LOM-ER-ACE) is a ribonucleoprotein enzyme complex ( a cellular reverse transcriptase) that has been referred to as a cellular immortalizing enzyme It stabilized telomere  lenth  by adding  hexamerie  (TTAGGG) repeats onto the telomeric ends of the  cgromosomes , thus compensating for the erosion of telomeres that occurs in its absence.

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Telomerase works by adding back telomeric DNA to the ends of chromosomes, thus compensating for the loss of telomeres that normally occurs as cells divide. Most normal cells do not have this enzyme and thus they lose telomeres with each division.

Dna helix structure closeup Premium Photo

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Replication of DNA with telomeres   -(A)  Formation of telomere   -(B)  role of telomerase in the replication of telomere (note: Only 2/3 repeat sequences of telomere shown for clarity)

TELOMERES

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