Telomeres are short nucleotide sequences found at the end of linear chromosomes which protect the genetic information. In vertebrates, telomeres have the hexameric sequence TTAGGG.
Elizabeth Blackburn and Joseph Gallworking in the 1970s discovered that telomeres at the end of chromosomes have DNA consisting of repeated similar units.
They also discovered that these repeated units of DNA within the telomeres protected the genetically significant central part of the chromosome from damage during cell division. The protection is necessary for two reasons:
(I)Enzymes involved in DNA synthesis are unable to synthesise the ends of one of the DNA strands. This is because in the double helix, one DNA strand “Chromatid” runs forward from the 5 carbon position in Ribose to end at the last Ribose with carbon 3 at the end of the chain of Ribose – Phosphate repeating units and the complementary strand in the opposite direction, i.e. 3 to 5.
(II)The second reason for the importance of telomeres is again found during DNA replication. Exposed lengths of single stranded DNA are liable to attach to each other, either in the same chromosome or between chromosomes. Such fusions could lead to apoptosis or cancer.
These are the two reasons why that are formed.