Tag Archives: DNA Polymerase

Mosaic Me

DNA polymerase (which copies our DNA during cell division) makes an average of one uncorrected mistake per 100,000,000 bases.  Given that our genome consists of three billion bases, this means that an average of 30 alterations are made each time our DNA is copied.  As a result, not only are some of our cells genetically different from the others, in truth few if any of them are 100% identical.  We are all mosaic creatures.

Some types of cells, such as epithelial cells, can produce a new “generation” once a day.  This means that after three years, some of our cells are part of generation 1,000, and by the time we are thirty years old, some of our cells are in generation 10,000, with DNA that has drifted from the divinely inspired parental genome by some 300,000 bases.  While that is still only 0.01%  of the total – i.e., one part in ten thousand – 300,000 is still an alarming number.  No wonder I don’t get along with myself as well as I used to.

This sort of thing does call into question the logic of using a cheek swab or a blood sample to calculate a person’s genetic code.  In some situations, a person might be told they are at a high risk of, say, liver cancer, when the applicable mutations don’t appear in liver cells at all.  The real problem, though, is to speak of a person’s genetic code as if it were a single thing.  Our bodies are like multi-core computers, where (a) each core is running a different variant of the operating system, (2) each of those variants is a mish-mash of different versions, and (d) none of those operating systems have been through any but the most rudimentary quality assurance testing.

Surely this situation calls for action.  Unfortunately, as I understand it, various individuals have contacted the Original Equipment Manufacturer (OEM) to complain, only to be told that the system warranty was rendered null and void during a previous epoch.  Something to do with a pilfered apple.  For my part, I feel we’ve been sold a lemon.

Rather than complain, however, let’s look at the bright side: we now have one more reason to embrace diversity and renounce bigotry.  Viva le difference.

The Unexplained Intelligence of DNA Polymerase

Consider DNA polymerase.  We’re told that this complex molecule copies DNA at a rate of 200 bases per second.  Note that in order to perform this task correctly, the molecule has to identify which of the four bases (CATG) it is attached to, then it has to snatch the complementary (not the identical) base out of the cytoplasm, which means it only has a 25% chance of grabbing the right one, yet it does so 99.9999% of the time.

But wait, there’s more.  If the DNA polymerase happens to insert the wrong base into the growing chain, it is able to detect its mistake, back up, extract the errant nucleotide, and then proceed where it left off.

To reiterate:  this is a molecule we’re talking about.  Never mind where this molecule came from:  explain to me how it works right now, inside the cells of your body, my body, and pretty much every eukaryotic organism on the planet.

This molecule, however complex, is an inanimate collection of atoms.  It has no nervous system.  Even if it performs its assigned task inside a neuron in your brain, still:  it’s inside the neuron, inside the nucleus of that neuron, copying a small stretch of DNA on a single chromosome. Common sense tells us that no inanimate molecule can do what DNA polymerase is doing:  not without an intelligent, guiding Hand.

So how do we explain the behavior of this thing?  Is God personally moving every single molecule in every single cell inside your body?  Moving every molecule in the universe?  Is God personally pushing protons together in the heart of every star in the universe to form helium?  Going down that path leaves us with an animist religion, where God is the universe, and vice versa.

Another problem with this approach is that DNA polymerase does make mistakes that go uncorrected.  This happens about once every 100,000,000 bases, which is an A+ anywhere in the galaxy.  Yet even with such a low error rate, an average of 30 mistakes are made every time a human genome is copied.  In some situations, those mistakes lead to birth defects, degenerative diseases, and cancer.  Is God personally picking victims, seemingly at random?

Here’s an even worse problem.  If God is moving molecules around inside our bodies, is there any point in trying to cure diseases?  Surely we wouldn’t be able to do such a thing, and even if we did manage to succeed, surely we would pay the price for having thwarted God’s will.  So is all medicine an affront to God?

None of those answers seems especially appealing, which leaves us with the alternative:  that DNA polymerase is indeed performing its task without divine intervention, being driven instead by Brownian motion, 3d stereochemistry, electromagnetic attraction, and the like.  For fundamentalists, this isn’t a good answer either, because it opens the gate.  If we can accept that this obviously intelligent behavior is being perpetrated by an inanimate molecule, why point to something like the eye and say “that’s obviously too complex to simply have evolved”?

If you can accept that the present-day behavior of DNA polymerase is driven by natural laws, then accepting that evolution is driven by natural laws is trivial by comparison.