Title:Long for This World: The Strange Science of Immortality
Author(s): Jonathan Weiner
Publisher(s): Ecco
Pages: 320
Year: 2011
Format: EPUB
Language: English
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Confusing things can happen in lysosomes, as in the fog of war. Cells can use them to devour invading parasites like the bacteria streptococcus. On the other hand, a cell that has been hurt or poisoned may devour a good part of its own substance and die. Nobody knows whether the cell is trying to kill itself or heal itself. Apparently the very same mechanism can promote survival and promote death. Perhaps when the cell devours itself too fast to rebuild, it dies.
It may be that our ability to maintain a healthy balance between the creation and destruction of molecules is what makes the difference, at the very finest scale of mortality, where we are examining life and death virtually one molecule at a time. Specialists in the lysosome, along with another cellular disposal unit, a stout, barrel-shaped structure called the proteasome, like to argue that housekeeping may turn out to be at the heart of it all. Many gerontologists think the Good Housekeeping people are a bit too enthusiastic; they think the self-cleaning, self-devouring work of autophagy is only a part of the problem of mortality. But it is certainly true that autophagy plays a role during the body’s time of growth, from embryo through youth to maturity. It is one of the ways the body sculptures itself to produce its final form, carving away webs between the fingers of the young embryo to produce the hand, or whittling away excess neurons from the brain of the infant to produce and refine each working mind. The machinery of autophagy is also important when aliens invade; when bacteria and viruses intrude on the body, some of the defensive work of demolition is done by autophagy. And autophagy is crucial at every moment of our lives in the nest of the Phoenix, where we are continually consumed and reborn. But our bodies are not designed to do it perfectly forever because our whole bodies are, in the last analysis, disposable.
It is easy to see how trouble in lysosomes might spiral out of control as we get older. For instance, free radical damage may interfere with the lysosome’s ability to digest big bites of the cell—macroautophagy. Then, because the lysosome can’t handle those big bites of the cell, more free radical damage builds up around it. When a cell is young, these bites really are gigantic. A healthy young lysosome can swallow a mitochondrion—it can take in a whole factory in one gulp. Because an aged lysosome can’t do that, more mitochondria that need scrapping may sit around unscrapped. And because the cell can’t swallow large chunks of itself at one go, billions of smaller molecular machines inside the cell have a longer “dwell time.” They sit around longer, increasing the chances that they will get bunged up and malfunction and make other stuff badly, which will then sit around, too, mucking things up.
- Рубрика: Фантастика
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