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In comparison, when cells were released and allowed to cycle, telomere length increased linearly with time. [34] These data suggest that telomere elongation occurs only in S phase. Additional experiments with greater time resolution support this hypothesis and narrow the timeframe to late S phase.
The telomere was first discovered by biologist Hermann Joseph Muller in the early 20th century. [4] However, experiments by Elizabeth Blackburn, Carol Greider, and Jack Szostak in the 1980s led to the successful discovery of telomerase (the enzyme responsible for maintaining telomere length) and a better understanding of telomeres. [5] [6] [7]
[49] [50] There is a Web-based Analyser of the Length of Telomeres , software processing the TRF pictures. [51] A Real-Time PCR assay for telomere length involves determining the Telomere-to-Single Copy Gene (T/S) ratio, which is demonstrated to be proportional to the average telomere length in a cell. [52]
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 ...
This inhibitive effect seems to function in a telomere length-dependent manner; [3] that is, TERRA levels inversely correlate with increased activity of telomere elongation. In general, TERRA has been shown to be most abundant in cells with long telomeres, [ 2 ] [ 3 ] while cells with short telomeres express comparatively lower levels of ...
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. The Hayflick limit has been found to correlate with the length of the telomeric region at the end of chromosomes.
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.
TERRA can also regulate telomere length by increasing euchromatin formation. [5] On the other hand, nonsense-mediated decay factor enrichment at telomeres may exist to prevent TERRA inhibition of telomerase. [1] TERRA levels vary during the cell cycle, decreasing during S phase, and increasing in the transition from G2 phase to G1 phase. [5]