Telomeres

General

Ends of eukaryotic chromosomes

• Prevent chromosome ends from fusing to other chromosomes

• Prevent DNA degradation from nucleases

• Assist DNA repair mechanisms in distinguishing DNA breaks

• Play a role in determining how many divisions a cell can undergo

Correlation with aging

Telomeres contain short nucleotide sequenes present (5-TTAGGG-3)

• Human somatic cells contain 500-3000 (5-TTAGGG-3) repeats at the ends of chromosomes

  • They shorten with age

    • Most human somatic cells die after 20-70 generations - Hayflick limit

Shortening

DNA polymerase 3 can only add nucleotides from 5prime - 3prime

• DNA polymerase 1 replaces all RNA primers

  • The first primer on the lagging strand can be removed but not replaced because the is no 3prime-OH from another primer existing

• Results in 50-100 bases lost each time DNA replicates

  • Telomeric DNA protects organisms genes

Protection

Act as bufers at the ends of linear DNA

• Everytime DNA replicates

  • Telomeres absor the loss of DNA tat occurs during replication

  • PRevents shortening of important genes

  • Prevent chromosome ends being recognized as broken DNA, avoding fusion or degradation