Space, Time and the DNA Continuum
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.
Labels: Biology, Cell Biology, Cell growth, DNA, DNA replication, Dolly, LiveScience, Telomere
posted by Madison @ 7:34 AM
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