Telomere

From ArticleWorld

The telomere is a region on the end of the chromosome that is made up of a repetitive sequence of DNA. This functions as a disposable set of DNA as its purpose is to avoid the loss of valuable genetic data. The enzyme DNA polymerase is only able to replicate DNA to a certain point on the chromosome. This means if genetic data at the ends were not repeated these would be lost.

Function

Telomeres are repeating sequences and proteins on the terminal ends of chromosomes that act to prevent fraying of chromosomes as well as loss of genetic information. They are extended by telomerases. The telomere sequence varies from organism to organism but, generally, tends to be rich in the bases guanine and cytosine.

Telomere shortening

This occurs in DNA replication in eukaryotes. As DNA replication occurs from the middle of the strand of DNA this causes the molecule being replicated by the enzyme DNA polymerase to develop a lagging strand. Problems arise here as in the lagging strand the direction of polymerization required is reversed to the 5' to 3' direction as opposed to the 3' to 5' direction.

This problem is overcome by short RNA sequences which attach to the lagging strand so that the enzyme can start replication from these points. Okazaki fragments are formed and the RNA sequences continue to move along the strand to facilitate the formation of the DNA. This continues until the last RNA attaches and is converted into DNA to seal the gaps between the Okazaki fragments. This is where a section of the telomere is destroyed by the enzyme converting the RNA to DNA resulting in shortening of the telomere.