Hayflick limit

Hayflick limit

The Hayflick limit is the number of times a cell will divide before it stops due to the telomere reaching a critical length [cite journal
author=Hayflick L.
title= The limited in vitro lifetime of human diploid cell strains.
journal=Exp. Cell Res.
year=1965
volume=37
issue=3
pages=614-636
pmid= 14315085
doi=10.1016/0014-4827(65)90211-9] .

It was discovered by Leonard Hayflick in 1965, at the University of California, San Francisco (UCSF), when Hayflick demonstrated that normal human cells in a cell culture divide about 52 times in 20% oxygen (i.e. practically normal air) or 70 times in 3% oxygen (which is the same as human internal conditions). It then enters a senescence phase (refuting the contention by Alexis Carrel that normal cells are immortal). Each mitosis shortens the telomere appendix on the DNA of the cell, thus ticking back an "inner clock" for each subsequent copy of the cell. Some organisms' cells do not encounter the Hayflick limit due to telomere lengthening, examples are long-lived sea-birds, whose cells are technically immortal.

This mechanism is believed to have evolved primarily to protect the body from creating a potentially-cancerous cell. Because of the fragmented way DNA replicates, a very short telomered cell may lead to genomic instability when the proteins meant to be located on the telomere will fail to attach and it will be marked as a double-strand DNA break, possibly leading to cancer.

Many stem cells, as they are undifferentiated, are not affected by the Hayflick limit. They exist in every tissue and may continue reproducing for the lifespan of the organism. To avoid reaching the barrier, cells that need to keep on dividing express the telomerase enzyme or use Alternative Lengthening of Telomeres mechanism. These methods are also used by cancer cells to divide uninhibited.

The normal Hayflick limit of cells in organisms other than humans varies, and affects their life span.

Carnosine can increase the Hayflick limit in human fibroblasts [cite journal
author=McFarlan GA.
coauthors=Holliday R.
title=Retardation of the senescence of cultured human fibroblasts by carnosine
journal=Exp. Cell Res.
volume=212
issue=2
pages=167-175
year=1994
pmid=8187813
doi=10.1006/excr.1994.1132] . It appears to reduce the telomere shortening rate as well [cite journal
author=Shao L
coauthors=Li QH, Tan Z
title=L-carnosine reduces telomere damage and shortening rate in cultured normal fibroblasts.
journal= Biochem Biophys Res Commun.
year=2004
volume=324
issue=2
pages=931-936
pmid=15474517
doi10.1016/j.bbrc.2004.09.136] .

ee also

*Apoptosis
*Biological immortality
*HeLa cells

External links

[http://www.newscientist.com/article/mg19626255.600-chromosome-caps-may-explain-cell-immortality.html Cell immortality and cancer]


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  • Hayflick limit — Hayflick limit. См. граница Хейфлика. (Источник: «Англо русский толковый словарь генетических терминов». Арефьев В.А., Лисовенко Л.А., Москва: Изд во ВНИРО, 1995 г.) …   Молекулярная биология и генетика. Толковый словарь.

  • Hayflick limit — Hay·flick limit (haґflik) [Leonard Hayflick, American microbiologist, born 1928] see under limit …   Medical dictionary

  • Hayflick limit — /ˈheɪflɪk lɪmət/ (say hayflik limuht) noun the number of times a normal cell population will continue to divide, each division shortening the telomeres on the DNA until cell division is no longer possible. {described in 1961 by Leonard Hayflick,… …  

  • Hayflick limit — the maximum number of divisions a cell can undergo before cell death, between 50 and 60 in most human cells. Some malignant cell lines escape the limit and undergo immortalization (q.v.) …   Medical dictionary

  • Hayflick limit — See cell death, cell line …   Dictionary of molecular biology

  • Hayflick — Leonard Hayflick (* 20. Mai 1928 in Philadelphia/Vereinigte Staaten) ist ein US amerikanischer Gerontologe. Bekannt wurde er vor allem durch seine Arbeiten auf dem Gebiet der Zellteilung, in denen er zeigte, dass normale Körperzellen sich nur… …   Deutsch Wikipedia

  • Hayflick-Grenze — Als Hayflick Grenze wird bei Eukaryoten die begrenzte Anzahl von Zellteilungen bezeichnet, denen sich eine Zelle unterziehen kann, bevor der Programmierte Zelltod eingeleitet wird, weil die Telomere eine kritische Länge erreicht haben. Benannt… …   Deutsch Wikipedia

  • Hayflick — Leonard, U.S. microbiologist, *1928. See H. limit …   Medical dictionary

  • limit — A boundary or end. [L. limes, boundary] critical l. the upper or lower boundary of a laboratory test result that indicates a life threatening value. elastic l. the greatest stress to which a material may be subjected and still be capable of… …   Medical dictionary

  • Leonard Hayflick — (born May 20, 1928), Ph.D., is Professor of Anatomy at the University of California, San Francisco, School of Medicine, and was Professor of Medical Microbiology at Stanford University School of Medicine. He is a past president of the… …   Wikipedia

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