Telomerase -
Ans. is 'b' i.e., Causes carcinogenesis o Telomerase is a DNA polymerase (RNA dependent DNA polymerase) which is present in germ cells and is absent from most somatic cells.o Thus telomerase activity and maintenance of telomere length are essential for the replicative potential in cancer cells.o After a fixed number of divisions, normal cells becomes arrested in a terminally nondividing state.# Haw does the normal cells count their divisions i.e. How, do the cells find out that now they do'nt need to divide furtherCells achieve this through telomer shorteningo Telomers are short repeated sequences of DNA present at the linear ends of chromosome that are important for ensuring complete replication of chromosome ends.o It consists of many arrays of TTAGGG repeats at terminal of 3' ending strand. It confers stability- to chromosomes.With each successive division there is some shortening of the telomers.o Once the telomers are shortened beyond a certain point the ends of the chromosome are seen as broken DNA, which signals cell cycle arrest.o The broken DNA leads to activation of p53 dependent cell cycle check points causing proliferative arrest or apoptosis.o P53 causes activation of CDK inhibitor p21 that inactivate cyclin D-CDK4 complex so that cell can not cross restriction point and can not enter into 'S'phase.o Thus telomere shortening functions as a clock that counts cell division.How do the germ cells keep on dividing throughout their life ???o In germ cells telomere shortening is prevented by the sustained function of the enzyme telom erase,o Telomerase is a reverse transcriptase and is responsible for telomer synthesis and maintaining the length of telomer.o it is RNA dependent DMA polymerase. It has one segment that is complimentary to TTAGGG repeat and is used as template for the replication of teiomeric sequence.o This enzyme is absent from most somatic cells and hence they suffer progressive loss of telomers and they exit the ceil cycle. Telomerase is present in Germ cells thus explaining the ability' of these cells to self replicate extensively. If loss of telomere is the basis offinite life span then how do cancer cells continue to divide actively ????o In cancer cells telomerase activity is reactivated. Telomerase activity has been detected in more than 90% of human tumours.o Thus telomerase activity and maintenance of telomere length are essential for the replicative potential in cancer cells.
RNA polymerase
Causes carcinogenesis
Present in somatic cells
Absent in germ cells
Cytogenetic Disorders