Tuesday, March 5, 2013

Space, Time and the DNA Continuum

Time. The great beyond, the relative, unfathomable, progression of the universe. Time, time, time. It’s what becomes of you.

This whole chain of thought started with telomeres. In case you don’t know, and I know some of you do, so I apologize in advance, your DNA replication only works one way. Without going into the big analogy to the New Jersey Turnpike I just made up, because it’s off-topic, I’ll simply put it this way: every time your DNA replicates, a little part of one end gets lost. Scary thought, isn't it? I mean, if that’s so, it serves as a useful explanation for stupid people, right? Their DNA must just replicate faster and thus they lose all sort of important genes.

Fortunately, this is not the case. Which leaves you to find another excuse for stupidity, but I’m sure you’ll manage. Your body has attached long bits of random repeated sequences to the ends of your chromosomes that don’t represent anything. Your DNA got tail, baby. And that tail is the telomere. The enzyme that attaches this tail, however, only works when you’re very very little (unless you have cancer, but it’s not the only wacky thing messing up during cancer), and then stops. Call it seriously early retirement if you like. This means your cells only have a certain number of replications before they start chopping into the Important Stuff, which usually causes them to die (in a very cool way, however - it looks a lot like a “splat” cartoon under the microscope, but really is a highly controlled explosion). But get this - the amount of tail chopped with every replication varies significantly, so there’s no real telling when you’ll get to the “point of no return.” And a lot of cells, for reasons we don’t understand, die “naturally” before they ever get into the DNA-chopping stage. But nevertheless, telomeres are very important, and are one of the many timing mechanisms of the cell.

There are many others, most of which are very poorly understood. Most cells aren't dividing - they’re just sitting there. Your liver cells, for example. Unless you do something profoundly necrotic, like become an alcoholic and destroy your liver, your liver cells replicate maybe once every few years. Obviously, this is asexual reproduction, because if it were sexual, there’d be a lot more of it. That said, your cells somehow know how many divisions they “are allowed” and die off after that number (and it’s pretty consistent among specific tissues. I believe liver cells get about 40 divisions each).

So the train of thought went like this in my mind this morning: “hmmm. telomeres. sucks to be the woman who cloned her cat for $50,000. life, the universe, and the definition of time. hmmmmmm.”

Now, you may be wondering why it “sucks to be the woman who cloned her cat for $50,000.” Well, barring the obvious attachment issues that led her to drop enormous sums on one cell when she could have maybe bought an entire animal shelter, there’s a simple problem with cloning. The DNA taken from the original cat is at a certain point in its “replication life cycle,” and that point is a lot further along than the original cells of an embryo. Which is to say, when the clone is born, its cells are already much older than the cells of all the other kittens on the block. This doesn't mean the kitten looks any different than any other kitten, but it does mean the kitten will age much more rapidly than those other kittens. This was the problem facing Dolly the sheep, and something that “science” has yet to overcome. So the woman who dropped the huge chunk of change isn't getting a cat for the next two decades, she’s getting a cat for a much shorter amount of time. I have no idea how aware of this she is, but I think it kinda sucks for her (given her aforementioned obvious attachment issues and all).

Then my mind sort of wandered off and started wondering how cells perceive time? I mean, technically we define time in I.S. units - seconds, minutes, etc…. But not always. Sometimes time is a distance “Just…. three…. more…. steps…. to…. the…ice cream!” Sometimes, it’s a list or a numbered set “Three questions to go, then it’s over.” Now, these things are also distances and lists in their own right, but we wrap time up in their definition, measuring the time of each question without resorting to minutes or seconds, but by the starting and stopping of the event - the exam. The exam is 40 questions long. Usually, this is then followed by “and you have 50 minutes to complete it in” but the initial measurement of the event is a set of numbered questions. It’s convoluted, but it’s a perceptual shift. And that’s what I’m getting to: the perception of time. We define time; we perceive it; time drags, speeds, slows, etc…. Time itself, however, is constant, not relative. It is our perception that is relative. How does a cell view time? In replication cycles? In nerve impulse firings? In glucose depletion and replenishment? Of course, that would require perception, which there’s no guarantee a cell has. But cells mark the passing of time - they start/live, grow and end/die. Bacteria, cells, plants, dingoes, etc, all mark the passing of time, with or without consciousness, by a different set of rules. That is to say, while it may be that only humans have a perception of time (and I have no thoughts on animals and this matter), all life has a definition of time, a unit of measurement. Cell cycles, seasons, sun-dark cycling, time outside a host/time inside a host. Beginning, middle, end. Life itself, being an event, is thus a definition of time. I wonder: do atoms also define time thusly? They have a spin, electrons have an orbit, things move, although there is no point at which they started or stopped moving, except in terms of temperature raising or slowing the spin. Does temperature impact atomic time - does it give the definition of time to the atom? Does the atom define time in temperature, then? Does the universe define time in the movement of atoms - in the location of molecules? Is time defined by Universe in terms of geography then? Is it really all about location, location, location?

Anyway, it was obviously a very stimulating virology lecture. The end result is that Science Theater today is a lesson in molecular biology’s Big Picture. Teensy-Tiny DNA vs. Goliath Time. Time is an enormous arrow; DNA is a tiny (yet powerful) trigger for the continuation of life. Time is the constant the universe defines in infinite and relative ways. Time is why you shouldn't clone your cat (or yourself?). Time was, I didn't think so much before my second cup of coffee. Time for another, I say.

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