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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]
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.
[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 ...
Cells may reduce their telomere length by only 50-252 base pairs per cell division, which can lead to a long lag phase. [ 59 ] [ 60 ] A telomerase activator TA-65 is commercially available and is claimed to delay aging and to provide relief from certain disease conditions.
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.
The discontinuous stretches of DNA replication products on the lagging strand are known as Okazaki fragments and are about 100 to 200 bases in length at eukaryotic replication forks. The lagging strand usually contains longer stretches of single-stranded DNA that is coated with single-stranded binding proteins, which help stabilize the single ...
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.