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Each time a cell undergoes mitosis, the telomeres on the ends of each chromosome shorten slightly. Cell division will cease once telomeres shorten to a critical length. [11] This is useful when uncontrolled cell proliferation (like in cancer) needs to be stopped, but detrimental when normally functioning cells are unable to divide when necessary.
The typical normal human fetal cell will divide between 50 and 70 times before experiencing senescence. As the cell divides, the telomeres on the ends of chromosomes shorten. The Hayflick limit is the limit on cell replication imposed by the shortening of telomeres with each division. This end stage is known as cellular senescence.
Telomeres at the end of a chromosome. The relationship between telomeres and longevity and changing the length of telomeres is one of the new fields of research on increasing human lifespan and even human immortality. [1] [2] Telomeres are sequences at the ends of chromosomes that shorten with each cell division and determine the lifespan of ...
When inflammation is present, this shortening happens faster. If telomeres become too short, cells may not be able to divide or work properly anymore, which may accelerate aging.
The successive shortening of the chromosomal telomeres with each cell cycle is also believed to limit the number of divisions of the cell, contributing to aging. After sufficient shortening, proteins responsible for maintaining telomere structure, such as TRF2, are displaced, resulting in the telomere being recognized as a site of a double ...
As telomeres shorten as a natural consequence of repeated cell division or due to other factors, such as oxidative stress, [19] shelterin proteins lose the ability to bind to telomeric DNA. When telomeres reach a critically short length, sufficient shelterin proteins to inhibit checkpoint activation are not available, although NHEJ and HR ...
Critically short telomeres trigger a DNA damage response and cellular senescence. [32] Mice have much longer telomeres, but a greatly accelerated telomere shortening-rate and greatly reduced lifespan compared to humans and elephants. [33] Telomere shortening is associated with aging, mortality, and aging-related diseases in experimental animals.
Alternative Lengthening of Telomeres (also known as "ALT") is a telomerase-independent mechanism by which cancer cells avoid the degradation of telomeres.. At each end of the chromosomes of most eukaryotic cells, there is a telomere: a region of repetitive nucleotide sequences which protects the end of the chromosome from deterioration or from fusion with neighboring chromosomes.