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Article:
Death, Aging, Rejuvenation (Part 2) by: Aleksandr Kavokin, MD,PhD Death Death. Why it happens? Why do we die? Why do animals die? Why do plants die? What is the need of this? In my opinion mechanism of death was selected during Evolution. From the position of Darwin's theory of Natural Selection everything, that benefits survival of species and gives advantage in Natural Selection, is preserved in following generations. Improvements were often left unchanged from the moment of life appearance. Though there could be other ways, certain mechanisms were accidentally selected. These improvements are reproduced in the genome of more complex species. Billions of years ago, according to the theory of evolution, chemicals randomly organized themselves into a self-replicating molecule. Lightings and UV-radiation helped to create first organic molecules. This phenomenon is reproducible in a lab. The experiments were described in 1950-60. First self-replicating molecules were probably RNA. First enzymes were probably RNA - enzymes. Then proteins, DNA and more complex lipid molecules and polysaccharide came to the scene. Death as it is did not exist at the stage of Primeval Soup . Sure some organic molecules were destroyed , some new created. But in general it was still that swirling and bubbling primary broth - quasi alive in our understanding as a mixture of biochemical reactions. Everything in the evolution was build from the previous blocks selected sometime by accident. Appearance of lipid membranes allows to compartmentalize the primary broth and create first cells. At the cellular stage we could already talk about the Death. Cell is destroyed, membrane is broken, everything leaked out. This is the Death. Content of cell inside lipid membrane is irradiated. Process of crazy molecular swirling is messed up by free radicals irreversibly. This is also signs of Death. Yet at the cellular stage we cannot talk about Aging. Death at this stage is accidental, not programed. Organic molecules may age (oxidation, conjugation, etc.) and cell would die. But damaged molecule are repaired or synthesized fresh usually. Hence, no good reason for a single cell organism to age. Irreparable damage from external cause leads to Death, not Aging. This is accidental death. For multicellular organisms, there is a parental organism that ages and eventually dies after next generation is born. For mono-cellular organism, there is parental organism that divides and becomes the next generation. There is no Aging leading to death of parental organism. Mono-cellular organisms are practically immortal in a right environment. Mechanism of division was selected during evolution. Cell has volume (3-D). Surface membrane is measured in square units (2-D). Growing beyond limits cause inadequate supply of nutrition from environment. Division solves the problem. Microbes, bacteria are immortal. Some divide every 20 minutes. In a an hour they multiply 8 times. Tumour cells divide slower. They are eukaryote. Most aggressive divide once a day. There is no need for Aging. They would die if you do not feed them. They die when you kill them with undiluted bleach in a flask. Otherwise they grow unstoppable. No aging. Multicellular organism supposedly has several control mechanisms to prevent excessive growth and division, to kill an extra cell. Apoptosis, programmed death, is used. Cancer cells often loose the control mechanisms. A scientist from Yale once pointed out to me that we can not say these cells are immortal. Maybe they divide and parental cell dies. Indeed. We do not follow the fate of every individual cell during experiments. They should give more children cells than parental cells die. Otherwise there would not be the multiplication. It is a possible scenario. We do not follow the fate of individual bacteria as well. Maybe they actually undergo aging. From the other hand some experiments suggest that new cells contain roughly half of the parent cell after division. So it is not Death or Aging. Next generations contain 1/'4
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