Extending the Telomeres

Although placing noncoding repeats at the ends of chromosomes protects chromosomes’ genes, the length of the telomeric repeats would dwindle over many replication cycles without a mechanism for replenishing them.

The telomere-replenishing mechanism depends on an enzyme named telomerase, first discovered in a chromosome-rich ciliated protozoan Tetrahymena. Telomerase is a ribonucleoprotein consisting of template RNA and a protein, TERT, that's a reverse transcriptase. Telomerase adds telomeric repeats to the 3′ end of a telomere.