Ends of chromosomes replicated by: (PGI Dec 2006)

Ans: A (Telomerase) TelomersThe ends of each chromosomeQ contain structures called telomers. Telomers consists of short repeat TG rich sequences.Telomerase is mutisubunit RNA-containing complex related to viral-RNA-dependent DNA polymerase (Reverse transcriptase), the enzyme which is responsible for telomere synthesis & thus for maintaining the length of telomereQ.Telomere shortening functions as a clock that counts cell divisionsTelomerase maintain telomer length by synthesizing telomereQTelomere shortening is associated with cancer and agingImportance of Telomers in:Ensuring the complete replication of chromosomal endsQProtecting chromosomal termni from fusion & degradationCentromere is an adenine - thymine (A-T)Q rich region, which connects sister chromatids Multiple rounds of cell replication |Short telemeresQ|||CheckpointintactCheck point bypassed:additional telomere shortening||||||ProliferativearrestApoptosisChromosomefusionNon-reciprocalrecombination |||Genomic instability|||Reactivationof telomeraseCell death| CANCERQ