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- Why did everyone start to hate the Russians if the U.S. did the same thing in Afghanistan, Iraq?
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People often die of old age only in books. A very small number of people manage not to acquire some dangerous disease by old age, or even several, which in adulthood does not seem so dangerous, but by old age, when the body is no longer able to effectively resist such “challenges”, they make themselves felt, significantly reducing the quality of life and its duration. There is also another aspect of aging, the answer to the question: why is a person's life limited? There is a Hayflick limit – the maximum number of divisions that a cell can perform without significant harm to its daughter cells. For most cells in the human body, this limit is ~52. As previously assumed, this is due to the fact that the enzyme DNA polymerase, which is responsible for doubling DNA during division, is not able to replicate (synthesize) nucleotides that are located at the edges of chromosomes (the so-called telomeres). With each cell division, if it does not have an active telomerase enzyme (as in all somatic – not sexual – human cells), a certain number of nucleotides carrying genetic information are lost at the ends of the chromosomes, which leads to various mutations. Now there is an idea that the Hayflick limit explains the activity of cellular recombinases that are triggered in response to age-related activation of mobile elements of the genome. When a cell loses its telomeres after all its divisions, it either remains in the same state as it was before (i.e., in the same state as before). it no longer divides), or ends its life with apoptosis (programmed cell death).