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Molecular and genetic theory of aging
It is peculiar to the person are afraid of aging, it conducts to a decline of his life. And human life in comparison with other processes of the Universe is very short. Therefore mental functioning at advanced age significantly differs from other periods of human life. To find a longevity elixir, many famous scientists tried to solve an aging riddle. But to find the answer it is necessary to get into secrets of the laws of nature. Today geneticists work on many questions, but the question of aging remains the biggest riddle.
The modern gerontology has several theories which give the chance to understand why the person grows old and dies. All of them have the right for existence, but the most recognized remains the molecular and genetic theory of aging. The hypothesis claiming that the reason of aging is covered in primary changes of the device of a cell is its cornerstone. But here as for process, here opinions of scientists do not meet as there can be two options, how exactly it happens and what it is caused by.
If to look at these two options of process, then it is simply impossible to disprove them. According to the first theory the mechanism of aging is genetically put in the cell, manifestations of an old age — the consistent pattern determined by the nature. In the second case it is only result of accumulation of mistakes in genetic memory which collected during evolution of living beings. So far preference behind the molecular and genetic theory with the first option of process of aging.
It is considered that the molecular and genetic theory of aging was created by A. Veysman who made a hypothesis of division of functions between somatic and sexual carriers of genetic material. Lack of aging in unicells is the cornerstone of this hypothesis. As Weismann's theory claims, the ratio between sexual and somatic cells defines life expectancy. Sexual or formative cells do not die as they bear in themselves the main genetic information, and here somatic are differentiated and die.
The first are responsible for information transfer in population, and the second provide their life activity. After the organism executed the purpose, having transferred populations information it becomes useless and somatic cells stop the division. The longer reproduction function duration, the is more than generations of somatic cells, respectively longer life expectancy. It can be considered as the natural selection provided by the nature.
In order that Weismann's theory was confirmed or disproved, the set of scientific researches is already conducted. During these researches consistent pattern between restriction of food and growth, and respectively and aging of an organism was determined. At food restriction the young organism slows down the growth owing to what puberty is late, it in turn slows down also aging. These experiences gave the chance to establish that aging is controlled by genes, as well as other stages of ontogenesis. At food restriction the organism needs more time to reach the final sizes, to execute the purpose in reproduction and to start a countdown, that is to begin to grow old.
The first denial of this theory gave A. Karrel's experiences. This French surgeon and the pathophysiologist developed technology of cultivation of culture of fabrics with use of a blood plasma and embryonal liquid. Its experiment with cells of the tissues of myocardium placed in a medium proved that the molecular and genetic theory of aging is not always right as the layer of cells shared unlimited number of times.
The molecular and genetic theory of aging of Veysman, found the continuation in Heylik's theory. Experiences of this scientist proved that the normal somatic cell has the strict number of divisions, this number, in honor of the scientist, called Heylik's number. According to this theory somatic cells have the limited mitotic potential and a certain life expectancy.
Example of such experience it is possible to observe when placing fibroblasts in a medium. The connecting fabric taken from an organism shares a certain number of times and perishes. But how A. Karrel's experiences? Difference between these researches consisted in the material. Karrel placed in nutritious mix pieces of fabrics, and Heylik single cells that yielded more exact results. The difference consisted also in nutritious mix. In Karrel's experiences together with blood and embryonal liquid to samples new cells got. Heylik in turn used solution of amino acids, salts and other low-molecular components. Thus, the molecular and genetic theory of aging was confirmed again, but it did not give the answer as the number of division and differentiation in all generations of cells is connected. The answer to this question was not given by the telomerny theory, it only allowed to establish that the structure which is responsible for the number of divisions – trailer sites of chromosomes, or telomeres.
At the end of HH-go of a century the new theory of aging in the course of which proof the telomerny theory was refuted was put forward. On a new hypothesis structures out of a cell kernel are responsible for aging of an organism, these are proteinaceous structures which participate in cell fission and are the division counter – centrioles. So the tsentriolyarny theory of Tkemaladze was born.
The Tsentriolyarny theory of Tkemaladze called the previous hypotheses into question, giving an indisputable fact. From a kernel of a somatic cell, perhaps to grow up the cloned animal, so it also bears in itself genetic information. Then it is more logical to assume that not the kernel, but structures in cytoplasm is responsible for aging.
Researches of cells led to conclusions that centrioles are responsible for this process. Before each division they double, and also direct forming of a framework of a cell – a cytoskeleton which plays an important role in cell life. The cytoskeleton coordinates association of cells in fabric and a metabolism of cells, is responsible for the initial stages of embryonic development. He is responsible for passing of external signals to a kernel, up to a signal on destruction of a cell. When the number of cell divisions is exhausted, centrioles perish, support of a cytoskeleton stops, so, the cell grows old and perishes. The exception is made only by cells capable to regeneration as, for example, cells of a liver of mature animals.
According to the tsentriolyarny theory of Tkemaladze there are immortal cells, cells of the higher plants, an oospore and some more types of initially deprived centrioles and a cytoskeleton consider such. Malignant cancer cells at which orientation of centrioles is sharply broken also belong to this list and the structure of a cytoskeleton is changed.
Aging of an organism begins when cells reached the limit of divisions. Such cells become differentiated, or specialized. In a human body the first differentiated are stem cells. Their majority has the suppressed division mechanism, it create a stock, all others go for forming of an organism. Gradually the stock is spent, for resuming of cells of fabrics when it is settled, stem cells do not renew it.
As the alternative to all above-mentioned hypotheses is put forward the theory of chance mutations, or mistakes in human genome. Researches of cells of long-livers are more senior than 100 years showed dominance of an allele apoye2, over an allele apoye4, and the last contributes to some diseases for example to a giperkhodesterinemiya and Alzheimer's disease. Dominance of one alleles over others can be considered as mutations. Change of apolipoprotein, a gene of the person who is responsible for longevity, can also lead to the fact that the organism grows old.
Molecules DNA are a basis of the genetic device, they can be damaged by physical or chemical agents, or so-called free radicals that breaks process of their division and can lead to their modification. Such influence on genetic material during evolution also led to aging of an organism.
Today thousands of researches are carried out, but these are only the next attempts in a long succession of searches of eternal youth. All previous theories of aging are not studied up to the end yet. Modern geneticists achieved tremendous result — having cloned an animal. Such achievements as increase in number of Heylik of divisions became on 20-30 result of work of many scientists, the marker of tumoral process is allocated that can help will win against cancer and other outstanding achievements. But ahead there is a lot more work of geneticists before the person finds eternal youth and immortality.
Section: Gerontology (Ageing)