Up to now, life expectancy has not increased due to the improvement of the human body, but due to the successful fight against unfavorable factors such as epidemics, hunger, hard working conditions. Having coped with viruses and developed technology, civilization has entered a stage where most people live safely to the natural limit of their age. But even with the most healthy lifestyle a person does not step over the physiological limit of 120 years. To move on, it is necessary to change not the external environment, but the body itself. And for this we need to understand the nature of death. It turns out that death is not necessarily the destiny of every organism. For example, in Hydra – a freshwater polyp from the group of jellyfish, there is a continuous renewal of cells of the body. With proper care, she lives indefinitely without showing signs of aging. Bacteria are immortal. Long-livers are some cancer cells. Even humans are partially "immortal": our blood, epidermal and gastric epithelial cells can be renewed without restrictions. So, unlimited longevity does not contradict the nature of life. To get closer to the solution of this mystery, biologists had to go down from the cell level to the step where the DNA.
Why bacteria do not grow old? Their DNA, unlike the DNA of other organisms, has the shape of a ring. When a cell multiplies, its "duplicate" is divided as follows. The circular DNA molecule "sits" special protein. He "crawls" on it, increasing the copy until it reaches the starting point. A duplicate of DNA is obtained without changes.
But hundreds of millions of years ago, more complex cells appeared. Their DNA exploded-the molecule has acquired the famous form of a double helix. Once the molecule is broken, its " tip " is no longer copied. Having reached the end, the enzyme does not feel the presence of DNA on both sides and stops working. Therefore, the next copy of DNA is a little shorter than the previous one, it is not accurate. But each piece is vital information. Cells multiply constantly, gradually they accumulate "errors".
DNA is restored in humans only at the beginning of his life – in the womb. Studies have shown that the fetus has a special protein that builds on the ends of the torn DNA molecule a certain text. But, when the baby is born, the enzyme somehow stops working. Accordingly, begin to accumulate errors in cell division, and we begin to age.