Telomerernas

Telomerernas are the protective caps at the ends of chromosomes. They are composed of repetitive nucleotide sequences and associated proteins. In humans, the telomere sequence is typically TTAGGG repeated many times. These repetitive sequences act like the plastic tips on shoelaces, preventing the ends of chromosomes from fraying or fusing with each other. Each time a cell divides, a small portion of the telomere is lost. This process is known as the end replication problem. Over many cell divisions, telomeres shorten significantly. When telomeres become too short, they can signal to the cell that it is time to stop dividing or undergo programmed cell death, a process called apoptosis. The enzyme telomerase is responsible for maintaining telomere length by adding back the repetitive sequences. Telomerase activity is high in germ cells and stem cells, allowing these cells to divide many times without critically shortening their telomeres. However, telomerase activity is generally low or absent in most somatic cells. The shortening of telomeres is thought to be a biological clock that contributes to cellular aging and the aging of the organism. Dysregulation of telomere length and telomerase activity has been implicated in various diseases, including cancer and premature aging syndromes.