The Role of Telomeres (Cambridge (CIE) AS Biology)

The Significance of Telomeres

• The ends of the chromatids in chromosomes are ‘sealed’ with protective structures called telomeres

  • They are made of non-coding DNA (DNA that does not contain genes) that is made up of short base sequences that are repeated many times (multiple repeat sequences)

• In telomeres, one strand is rich in the base guanine (G) and the other strand is rich in the complementary base cytosine (C)

• The main function of telomeres is to ensure that the very ends of the DNA molecules are included in DNA replication during mitosis

  • This is because the copying enzyme responsible for DNA replication is unable to run right to the very end of the DNA molecule and stops a little short of the end

  • If this end part of the DNA molecule contained an important gene, that piece of genetic information would be lost during DNA replication

  • In each subsequent cell division, a little more genetic information would be lost

• Telomeres therefore act as a ‘buffer’ region of non-essential DNA and ensure that no important coding sections near the ends of the DNA molecules are left out of the replication process

  • This ensures no genes are lost during cell division (the loss of vital genes can even result in cell death) and allows for continued replication of a cell

• To avoid the risk of losing genes most cells have an enzyme called telomerase that adds additional bases at each end (the telomeres)

• Some cells (generally specialised cells) do not have telomerase to ‘top up’ their telomeres and therefore after a certain number of cell divisions the cell dies, this has been connected with the ageing process

A telomere with multiple repeat sequences