What Is the Hayflick Limit?

The Hayflick limit is a concept, explaining the process of cellular aging in human cells.
According to the Hayflick Limit, a normal cell can only replicate and divide forty to sixty times before it can no longer divide, due to programmed cell death.

The concept of the Hayflick Limit, coined by Lonard Hayflick in 1965, helped scientists study the effects of cellular aging on human populations from embryonic development to death, including the discovery of the effects of shortening repetitive sequences of DNA, called telomeres, on the ends of chromosomes. Elizabeth Blackburn, Jack Szostak and Carol Greider received the Nobel Prize in Physiology or Medicine in 2009 for their work on genetic structures related to the Hayflick Limit.

The discovery of the Hayflick limit represented a radical change in the way science looked at cellular reproduction. Before the doctor’s discovery, cells were thought to be capable of immortality. Although the phenomenon of the Hayflick limit has been studied only in vitro, it eventually came to generally be accepted in the scientific community as fact. For decades, it looked like the limit was insurmountable, and it still appears that way. In 1978, however, the discovery of a segment of non-replicating DNA in cells called telomeres shed light on the possibility of cellular immortality.

Scientists used Hayflick’s theory in support of further studies about cellular aging, especially with research in telomeres, which are repetitive sequences of DNA at the ends of chromosomes. Telomeres protect the chromosome from folding in on itself, and they decrease mutations in the DNA.

The ends of chromosomes carry structures called telomeres. Every time a cell divides the telomeres become shorter, this loss being the basis of what Hayflick described not as a clock (the process is not dependent on measuring time) but as a counting device, a “replicometer”.

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Branka Duric

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