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The Hayflick limit is the number of times a cell will divide before it stops due to the telomere
Telomere

A telomere is a region of repetitive DNA at the end of chromosomes, which protects the end of the chromosome from destruction. Its name is derived from the Greek nouns telos "end" and mer?s "part"....
 reaching a critical length.

Overview
The Hayflick limit was discovered by Leonard Hayflick
Leonard Hayflick

Leonard Hayflick , Doctor of Philosophy, 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....
 in 1965, at the University of California, San Francisco
University of California, San Francisco

The University of California, San Francisco is one of the world's leading centers of health sciences research, patient care, and education. UCSF's medical, pharmacy, dentistry, nursing, and graduate schools are among the top health science professional schools in the world....
 (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).






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The Hayflick limit is the number of times a cell will divide before it stops due to the telomere
Telomere

A telomere is a region of repetitive DNA at the end of chromosomes, which protects the end of the chromosome from destruction. Its name is derived from the Greek nouns telos "end" and mer?s "part"....
 reaching a critical length.

Overview


The Hayflick limit was discovered by Leonard Hayflick
Leonard Hayflick

Leonard Hayflick , Doctor of Philosophy, 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....
 in 1965, at the University of California, San Francisco
University of California, San Francisco

The University of California, San Francisco is one of the world's leading centers of health sciences research, patient care, and education. UCSF's medical, pharmacy, dentistry, nursing, and graduate schools are among the top health science professional schools in the world....
 (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
Senescence

Senescence encompasses all of the biological processes of a living organism's approaching an advanced age . The word senescence is derived from the Latin word senex, meaning "old man" or "old age" or "advanced in age"....
 phase (refuting the contention by Alexis Carrel
Alexis Carrel

Alexis Carrel was a French people surgeon, biologist and eugenicist, who was awarded the Nobel Prize in Physiology or Medicine in 1912....
 that normal cells are immortal
Biological immortality

biology immortality can be defined as the absence of a sustained increase in Mortality rate as a function of chronological age. A cell or organism that does not experience, or at some future point will cease, senescence is biologically immortal....
). Each mitosis
Mitosis

Mitosis is the process in which a eukaryotic cell separates the chromosomes in its cell nucleus, into two identical sets in two daughter nuclei....
 shortens the telomere
Telomere

A telomere is a region of repetitive DNA at the end of chromosomes, which protects the end of the chromosome from destruction. Its name is derived from the Greek nouns telos "end" and mer?s "part"....
 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; for example, the cells of some long-lived sea-birds such as Leach's Petrel are technically immortal.

This telomere lengthening mechanism is believed to have evolved primarily to protect the body from creating a potentially cancerous cell. Because of the fragmented way DNA
DNA

Deoxyribonucleic acid is a nucleic acid that contains the genetics instructions used in the development and functioning of all known living organisms and some viruses....
 replicates
DNA replication

DNA replication, the basis for heredity, is a fundamental process occurring in all living organisms to copy their DNA. This process is "semiconservative replication" in that each strand of the original double-stranded DNA molecule serves as template for the reproduction of the complementary strand....
, 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
Cancer

Cancer is a class of diseases in which a group of cell display uncontrolled growth , invasion , and sometimes metastasis . These three malignant properties of cancers differentiate them from benign tumors, which are self-limited, do not invade or metastasize....
.

Many stem cell
Stem cell

Stem cells are Cell found in most, if not all, multi-cellular organisms. They are characterized by the ability to renew themselves through Mitosis cell division and Cellular differentiation into a diverse range of specialized cell types....
s, 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
Telomerase

Telomerase is an enzyme that adds specific DNA sequence repeats to the 3' end of DNA strands in the telomere regions, which are found at the ends of eukaryote chromosomes....
 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
Carnosine

Carnosine is a dipeptide of the amino acids beta-alanine and histidine. It is highly concentrated in muscle and brain biological tissues.A small 2002 study reported that carnosine improved on a measure of socialization and receptive vocabulary in children with autism....
 can increase the Hayflick limit in human fibroblasts, as well as appearing to reduce the telomere shortening rate.

See also

  • Apoptosis
    Apoptosis

    Apoptosis is the process of programmed cell death that may occur in multicellular organisms. Programmed Cell death involves a series of biochemical events leading to a characteristic cell Morphology and death, in more specific terms, a series of biochemical events that lead to a variety of morphological changes, including Bleb , changes...
  • Biological immortality
    Biological immortality

    biology immortality can be defined as the absence of a sustained increase in Mortality rate as a function of chronological age. A cell or organism that does not experience, or at some future point will cease, senescence is biologically immortal....
  • HeLa cells
    Hela

    Hela can stand for:* Hela, an ancient name for Sri Lanka* Hela , a name for the Sinhala people of Sri Lanka* Hela means restroom in Turkish....


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