Which enzymatic mutation is responsible for immortality of cancer cells :

Ans. is 'c' is Telomerase " Telomeres are short repeated sequences of DNA (TTAGGG) that compose the linear ends of chromosomes and are important inensuring the complete replication of chromosome ends and,protecting chromosomal termini from Fusion and degradation.The sequences are formed by a specialized Ribonucleoprotein, telomerase, an enzyme that stabilizes telomere length by adding to the ends of chromosomes. The activity of telomerase is repressed by regulatory proteins, which restrict telomere elongation, then providing a length sensing mechanism. Telomerase activity is expressed in germ cells and is present at low levels in stem cells, but is usually absent in most somatic tissues.When somatic cells replicate, a small section of telomere is not duplicated and telomeres become progressively shortened. Shortened telomeres are proposed to signal a growth check point allowing cells to become senescent. Conversely in immortal cancer cells, telomerase is reactivated and telomeres are not shortened, suggesting that telomere elongation might be an important, possibly essential step in tumor formation