Chapter 15 cell organelles

We seem to be living through a biological revolution—at least so far.But the revolution didn't mess us up, or even disturb us much.Even if we don't fully understand what it is, we're learning to take it for granted.It's a weird, peaceful revolution.In this revolution, there is no such thing as panic and fear that old ideas will be denounced and overthrown.Instead, whole, chunks of new knowledge are being brought in almost every day, to be placed where there were previously blank spots.The news about DNA and the genetic code does not displace some old dogma where there was nothing to be sidelined.Molecular biology does not reject old theories about the inner details of cellular function.We seem to be starting from scratch, from scratch.

Not only do we take it for granted—we tend to talk about revolutions in biology as if expecting to profit from them, just as we did with the Industrial Revolution last century.All kinds of revolutionary changes in technology, from the ultimate control of human disease to the solution of the world's food and population problems, are assumed to be for the future.We have even debated what kind of future we like and what kind of future we are willing to cancel.Issues such as the value of genetic engineering, the creation of desirable human clones from a single cell, and even the possibility that two heads are truly smarter than one have been debated at several conferences.

So far, we seem to have been really shocked by nothing in the new knowledge.People have felt strange, even consternated, but not yet panicked.Maybe it's too early to expect this, maybe it's just around the corner. But it's not too early to look for trouble.I can sense some, at least to me.I realize these troubles from what I know about organelles.I was brought up with the belief that organelles are little invisible engines inside my cells, owned and manipulated by me or my cellular agents, little microscopic things that are private to my intelligent body .But now it seems that some of them, and indeed some of the most important ones, are completely unknown.

The evidence is strong and direct.The mitochondrial inner membrane is not like the cell membrane of other animals, but most like the membrane of bacteria.Mitochondrial DNA is qualitatively different from animal cell nucleus DNA, but it resembles bacterial DNA; in addition, like microbial DNA, it is closely connected with the membrane.Mitochondrial RNA is the same as organelle RNA, but not the same as that of the nucleus.The ribosomes in mitochondria are like bacterial ribosomes, but different from animal ribosomes.Mitochondria are inherent, they have always been there, replicating and multiplying on their own, and have nothing to do with the reproduction of the cells in which they are located.They are passed from egg to newborn; a few are passed down from sperm, but most are from the mother.

Likewise, chloroplasts in all plants are independent, self-replicating residents with their own DNA, RNA, and ribosomes.In terms of structure and pigment content, they mirror the prokaryotic blue-green algae.It was recently reported that the nucleic acids of chloroplasts are actually homologous to the nucleic acids of some photosynthetic microorganisms. Maybe there are more.It has been suggested that flagella and cilia were once spirochetes that merged with other prokaryotes during the formation of nucleated cells.Some believe that centrioles and basal bodies are semiautonomous organisms with their own independent genomes.There may be others, as yet undiscovered.

I just wish I could retain ownership of my own nucleus. It's amazing how calmly we accept such information, as if it just fits with a notion we've always had.In fact, the possibility that chloroplasts and mitochondria might be endosymbionts had been suggested as far back as 1885, but one would still expect that confirmation of the notion would send researchers shouting in the streets.However, this is a contemplative, industrious field, where work is well underway, with special attention now being paid to the molecular genetics of organelles.There has been careful, measured thought about how they got there in the first place, and the consensus has been that they were probably swallowed up by larger cells about a billion years ago and have remained in the There.

The usual view is to see them as enslaved organisms, captured to provide ATP for cells that cannot breathe themselves, or carbohydrates and oxygen for cells that are not equipped for photosynthesis.This master-slave relationship is the common view of some biologists.They were also fully fledged biologists, all eukaryotes.But there is another side to the story.Viewed from the standpoint of organelles, it can be argued that they learned early on the best kind of life, the one with which they live with the least effort and with which they and their offspring take the least risk.They are not like us.We have evolved along the way, painstakingly producing longer and longer strands of DNA, taking greater and greater risks—maybe someday some mutation will occur and send us to an evolutionary dead end.They are the opposite.They decided not to grow up any longer, and to keep their duties as a group.To this end, to ensure that they last as long as possible, they penetrate us and all living things.

Mitochondria and chloroplasts have always been small, conserved and stable.That's a good thing for the whole enterprise, because these two organelles are fundamentally the most important living things on Earth.The two work hand in hand to create oxygen and arrange its use.In fact, they run life. My mitochondria make up a huge part of who I am.I can't count for sure, but I think, drying them, they're almost as big as the rest of me.In this light, think of me as a colony of large, mobile, breathing bacteria manipulating a complex system of nuclei, microtubules, and neurons, working for the bacteria's domestic pleasure and livelihood , and at this time, he was manipulating the typewriter.

I am inseparable from my mitochondria and have to do a lot of vital work for them.My nucleus is genetically coded to create the outer membrane of each mitochondria, and I have to synthesize the bulk of the enzymes that attach to the mitochondrial cristae.It is said that each of them only produces a small amount of matter that is only enough to survive on its own, and I must provide the rest.And all my worries and worries are mine. Knowing the situation, I can find all sorts of things to worry me about, such as viruses.If my organelles are really symbiotic bacteria colonizing me, how can I prevent them from getting viruses?Or, if they have such a thing as lysogeny, how can I prevent them from delivering phages to other organelles?Then there's the issue of my property rights.Are my mitochondria all dying with me?Do my kids get their mother's mitochondria and some of mine?I know this kind of thing shouldn't bother me, but it does.

Finally, there is the big question of my identity, and even my dignity as a human being.When I first knew that I was born from a lower life form, I didn't care.I pictured in my mind a family of thick-browed, protruding, speechless, hairy apes that inhabited the woods and never objected that they were my ancestors.To be honest, as a Welshman, I am even more proud to know that I have evolved significantly above them.It is a source of satisfaction to be able to be part of the process of improvement of the species. That's not all the problems.It never occurred to me that my origin was a cell without a nucleus.Let's just say that, if that's the end of it, I can live with it.But now there's an added layer of shame, saying that in some real sense I'm not descended from some ancestor at all, I've always carried all these things with me, or maybe they've always carried me.

In such a situation, there is no use in maintaining one's dignity, and it is best not to try to maintain it.It was incredible that they were here, moving around in my cytoplasm, breathing for my own muscles, but strangers.They are not so much related to me as they are to each other and to the free-living bacteria down there at the foot of the mountain.They felt like strangers, but then it occurred to me that the same creature, exactly the same creature, lived in the cells of the seagull over there, and in the cells of the whale, and the dune grass, and the seaweed, and the hermit crab; Also in the beech leaves in my back yard, in the skunk nest under the fence in my back yard, and even in the fly in the window.Through them, I relate to these.My next of kin--only one step further than my next of kin--is all over the world.This is new knowledge for me, and I'm a bit sad that I can't keep in closer touch with my mitochondria.If I pay attention, I can imagine I feel them: they don't squirm very much, but there is some kind of tremor now and then.I can't help but think that if I knew more about them, and more about how they keep them and I in sync, I'd have a new way of understanding music. In all symbiotic relationships, there is an inherent kindness, that's for sure.But this one -- quite possibly the oldest and most established -- seems especially fair.It doesn't look like the law of the jungle at all, and neither side poses as an enemy.If you're looking for something resembling a natural law to replace the "social Darwinism" of a century ago, you'll have to take lessons from the meaning of life implied by chloroplasts and mitochondria.It's laborious, but it can be found.