Why do people grow old# ?

Ancient emperors were obsessed with taking "elixir". In modern society, there are all kinds of drugs that claim to "prolong life and restore youth." Immortality "is the wish of human beings for thousands of years. With the progress of medical treatment and the improvement of living conditions, people's life expectancy is getting longer and longer. Statistics in 2009 show that the average life expectancy of Chinese has reached 73 years, including 71.3 years for men and 74.8 years for women. Looking around us, there are 80 or 90 year olds everywhere, and news about centenarians is also heard from time to time. However, so far, the life span of the longest living people in the world is only over 120 years old. Why can't we live forever? Why do people get old?

Body: a sophisticated and complex machine

The simplest answer to the aging of organisms is that organisms (such as the human body) are like a very complex and sophisticated machine. Machine used for a long time, will always cause wear and tear, exposed a variety of problems. It's the same with people. Whether it's organs or cells, the molecules in them are gradually damaged, and the wastes are constantly accumulating. Finally, there are always times when they lose their functions. This statement is most easily accepted, but what is the specific mechanism? People don't know.

The "deoxyribonucleic acid" (abbreviated as DNA) in cells, carrying the genetic information of each person's body, will be constantly damaged by chemicals and rays (such as ultraviolet) in our life. Although there is a whole set of mechanisms in cells to repair damaged DNA, once this repair mechanism itself is damaged, cells and human body will accelerate aging. For example, the phenomenon of "accelerated aging" in patients with "Werner syndrome" tells us that the destruction of DNA integrity is one of the mechanisms of aging.

Oxygen: a double edged sword of life activity

Our bodies can't leave oxygen for a moment. Only it can make us fully "burn" the "fuel" in food and supply energy to our body. But oxygen is a very active molecule, in vitro can make iron rust, make cooking oil become "Ha La". In our body, it will also compete with many molecules for electrons and destroy their structures. The common "destructive substance" in these chemical reactions is the "free radical" (also called "free radical") formed by oxygen. As people get older, more and more molecules are destroyed by oxygen "free radicals", and cells and bodies are gradually aging. In order to deal with these oxygen "free radicals", we have some proteins in our body, which can break down some of these harmful substances and make them harmless. One such protein is called "superoxide dismutase", abbreviated as sod. Animal experiments show that if the SOD gene is knocked out artificially, the life span of these organisms will be shortened. And if you raise the level of SOD in the body, these organisms will live longer. However, the increase of SOD does not make the organism "immortal", indicating that there are other mechanisms of aging.

Every day a lot of oxygen enters the lungs and is transported to all parts of the body

Cell: can you divide infinitely if you have enough to eat and drink

In 1961, American scientist hayfrick made an interesting research. He first took "fibroblasts" from the lungs of the fetus and cultured them in vitro with adequate nutrition. At first, these cells divide normally, and they seem to be full of vitality, as if they can proliferate indefinitely. But after about 50 equal divisions, the cells no longer divide and enter the "old age" stage. Will fetal and adult cell life be the same? To find out, he took "fibroblasts" from the lungs of adults and found that they only divided about 20 times in vitro and then stopped. This suggests that the number of cell divisions is related to the life span of the body that supplies the cells.

Hefrick and other scientists also compared the number of division of "fibroblasts" in different animal embryos, and found that the longer the life of organisms, the more times "fibroblasts" can divide. For example, a turtle that can live for 175 years can divide its embryonic fibroblasts 90-120 times, while a mouse that can live for 2-3 years can only divide its embryonic fibroblasts 8-11 times. Fibroblasts from patients with Werner's syndrome can only divide 2-4 times. This indicates that the number of cell division is closely related to the average life span of the animals that provide cells. What is the mechanism that determines the number of cell divisions?

Telomere: the timer of life

It turns out that a structure called "telomere" is the hand behind cell division. It is located at the end of the chromosome, just like the "shoelace head" made of metal wrapping on the shoelace head, which prevents the DNA double helix in the chromosome from loosening and maintains the stability of the DNA structure. For many cells in the body, the chromosome is duplicated every time they divide, and the "shoelace head" is shortened. When the "shoelace head" is almost "used up", DNA becomes loose and unstable, just like shoelaces without "shoelace head", and cells are close to death. So "telomeres" are like the "clock" of cell life, "ticking" to "tell" how long the cell has to live.

These are just a few of the mechanisms that cause aging. They are different from each other, but they work together. At present, the understanding of biological aging mechanism is far from enough, and scientists need to continue to work hard to uncover the truth of aging for us.

Telomeres are located at the end of chromosomes