Al Stahler: Invasion of the Body Snatchers
This is no movie. This is real. They are trying to hijack our bodies.
Plants must build leaves and stems. Plant-eaters must roam about, look for edible plants, munch them, digest them, then build their own bodies.
Animals further up the food-chain must hunt their prey, chase it down, chomp and digest and, like those above, build their bodies.
None of these activities happens by itself … all take energy. It takes work to keep oneself alive, to grow, to reproduce.
Some organisms manage to avoid most of that work: Parasites. The tapeworm anchors itself in your gut, and absorbs pre-digested food. No hunting, no grazing — and yet, the tapeworm has not escaped work entirely. The worm must still expend energy to build its body, to reproduce.
Leaving all these jobs to its host, the ultimate parasite would do no work at all.
We build our bodies with machines – tiny machines – made of protein. When we need a body part, we first build the machines that will then build that part. The instructions for building these machines are stored in our genes, which are composed of DNA. When we need something built, machines that can read DNA find the relevant instructions, and go to work.
All this work takes place in our cells. A recent estimate put the number of cells in the human body at something over 30 trillion — thirty million million. Cells are really small.
Surrounding the cell — keeping stuff from slopping out — is the cell membrane. The outer surface of the membrane looks like a three-dimensional jig-saw puzzle — the surface juts in and out, like the tabs on a puzzle piece that jut out, and the hollows that jut in, that we must match up to assemble the puzzle. But the pattern of shapes on the surface of the cell is not random — the innies and outies combine to make a signature — a signpost — identifying species (human, dog, goat) and type of cell (lung, liver, kidney).
Also scattered across the surface of the cell are regions of electric charge — much like the electricity that makes plastic peanuts stick to one’s clothes. Again, the pattern of charge is not random, but relates to species and organ.
More than just a signpost, the cell surface is a docking port. Suppose one part of your body wants to send a signal to another part. The signal comes attached to another puzzle piece, this one a mirror image of the cell surface, allowing it to recognize, then attach to — dock with — the cell.
The act of docking triggers the cell to pull the messenger inside.
Cells may be small, but viruses are tiny. A typical virus consists of a half dozen, maybe a dozen, genes (versus 20,000-plus in nearly every human cell), packed into a protein shell. The shell is studded with innies and outies, with regions of electric charge, mirroring the pattern on the cell surface — another jigsaw puzzle piece.
The virus docks with the cell … docking triggers the cell to pull it in … and all hell breaks loose. The viral capsule disintegrates, releasing the viral genes into the cell. Somehow — no one’s yet figured out how — the virus shuts down the cell’s normal work, and commandeers the cell’s machinery, forcing the cell to do nothing but make copies — thousands and thousands of copies — of the viral genes … and then package them in a shell.
Our ancestors’ cells have evolved with viruses for billions of years. We have defenses … not least, when a cell realizes it’s been hijacked, it’s programmed to commit suicide. Somehow, the virus shuts down our defenses.
Having made a multitude of copies, the cell bursts, releasing the new viruses into the body … perhaps into the nasal cavity, where they can be sneezed out, to infect more victims.
Every species, every organ, has its own jigsaw puzzle pattern, that the virus mirrors. So many viruses are species- or organ-specific. But sometimes the pattern — even if it doesn’t match — the pattern can be close enough for a virus to dock anyway, and infect a host of a different species … allowing a human victim to contract bird flu … or swine flu … or bat flu.
When our cells reproduce, we do our best to faithfully copy our DNA — to keep our genetic code accurate. Viruses, on the other hand, are programmed to make lots of mistakes … giving a new virus opportunities to evolve into a better fit to its new host.
Al Stahler enjoys sharing nature with friends and neighbors. His science and nature programs can be heard on KVMR (89.5 FM), and he may be reached at firstname.lastname@example.org.
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