Enzyme which prevents aging/senscence is -

Ans. is 'a' i.e., Telomerase Telomers and Telomeraseo Telomers are short repeated sequences of DNA present at the end of eukaryotic chromosomes.o In normal cells, telomeres get shortened in each replicated cycle. After the telomers get shortened by a critical length, cell stops dividing and enters into Go phase (senscence).o However, germ cells, cancer cells and stem cells have an enzyme telomerase (telomerase activity) which prevents telomer shortening. Thus telomers are not shortened in these cells, and therefore these cells have ability to self replicate extensively.o Telomerase is a reverse transcriptase (RNA dependent DNA polymerase) and is responsible for telomer synthesis and maintaining the length of telomers (replication of end of chromosome). Thus, telomerase provide longetivity to the cells which contain this enzyme.o Telomerase is absent from most of the somatic cells and hence they suffer progressive loss of telomers and they exit the cell cycle.o Senscent cells lack telomerase so their telomers get shortened by critical length and these cells remains in Go phase.