The Hayflick Limit PDF

The Hayflick Limit The number of times a normal [somatic](https://en.m.wikipedia.org/wiki/Somatic_cell), [differentiated](https://en.m.wikipedia.org/wiki/Cellular_differentiation) human cell population will divide before [cell division](https://en.m.wikipedia.org/wiki/Cell_division) stops describes...

The Hayflick Limit The number of times a normal [somatic](https://en.m.wikipedia.org/wiki/Somatic_cell), [differentiated](https://en.m.wikipedia.org/wiki/Cellular_differentiation) human cell population will divide before [cell division](https://en.m.wikipedia.org/wiki/Cell_division) stops describes the Hayflick limit. Leonard Hayflick demonstrated that a normal [human](https://en.m.wikipedia.org/wiki/Human) [fetal](https://en.m.wikipedia.org/wiki/Fetus) cell population will divide between **[40 and 60 times]** in [cell culture](https://en.m.wikipedia.org/wiki/Cell_culture) before entering a [senescence](https://en.m.wikipedia.org/wiki/Cellular_senescence) phase. (it is a point of debate among researchers what this number might be in living organisms rather than in a laboratory setting). This finding refuted the previously accepted view that normal cells are [immortal](https://en.m.wikipedia.org/wiki/Biological_immortality). Hayflick interpreted his discovery to be aging at the cellular level. The aging of cell populations appears to correlate with the overall physical aging of an organism. The Hayflick limit has been found to correlate with the length of the telomeric region at the end of chromosomes. During the process of [DNA replication](https://en.m.wikipedia.org/wiki/DNA_replication) of a chromosome, small segments of DNA within each [telomere](https://en.m.wikipedia.org/wiki/Telomere) are unable to be copied and are lost. The telomeric region of DNA does not code for any protein; it is simply a repeated code on the end region of linear eukaryotic chromosomes. After many divisions, the telomeres reach a critical length and the cell becomes senescent. It is at this point that a cell has reached its Hayflick limit. Hayflick was the first to report that only cancer cells are immortal. This could not have been demonstrated until he had demonstrated that normal cells are mortal. [Cellular senescence](https://en.m.wikipedia.org/wiki/Cellular_senescence) does not occur in most [cancer cells](https://en.m.wikipedia.org/wiki/Cancer_cell) due to expression of an [enzyme](https://en.m.wikipedia.org/wiki/Enzyme) called [telomerase](https://en.m.wikipedia.org/wiki/Telomerase). This enzyme extends telomeres, preventing the telomeres of cancer cells from shortening and giving them infinite replicative potential. A proposed [treatment for cancer](https://en.m.wikipedia.org/wiki/Experimental_cancer_treatment#Telomerase_therapy) is the usage of telomerase [inhibitors](https://en.m.wikipedia.org/wiki/Enzyme_inhibitor) that would prevent the restoration of the telomere, allowing the cell to die like other body cells.