<prompt> Ends of chromosomes replicated by: PGI Dec 2006TelomeraseCentromereRestriction endonucleaseExonuclease  <response>: 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-TQ rich region, which connects sister chromatids Multiple rounds of cell replication Short telemeresQCheckpointintactCheck point bypassed:additional telomere shorteningProliferativearrestApoptosisChromosomefusionNon-reciprocalrecombination Genomic instabilityReactivationof telomeraseCell death CANCERQ 