Map of life expectancy at birth from Global Education Project.

Saturday, September 06, 2008

Viruses for Dummies

There are plenty of excellent on-line biology courses, and I'm not trying to compete with them. If you really want to spend the time and effort to get into it, this is not a bad place to start learning about human cells. I'm not even a real doctor -- I'm a doctor of philosophy -- and I'm not even a real scientist -- I'm a social scientist -- so it would be ridiculous for me to try to reinvent the excellent work of biologists who totally know their stuff. But what I want to do here is something different. This is a practical experiment in health communication.

I'm imagining that I'm talking to somebody who has been diagnosed with HIV infection, who maybe didn't pay a whole lot of attention in high school biology class. The person might have gone on to college and majored in art history, or might never have graduated from high school. Either way, I don't want to confuse you, and I don't want to bore you, but I want to tell you what you need to know to understand what's going on with your health and your treatment. Maybe that's you, with or without the HIV, in which case you can critique my success in communicating; or maybe you know a lot about biology, in which case you can critique me for accuracy and completeness. I can take it.

This will take a few posts, so let's get started.

I've said before that while the question "what is life" may be philosophically profound in some ways, if we're talking about life on earth, there's a simple answer. Life is cells. There isn't anything we call life that doesn't consist of cells. There are these things called viruses which are not cells, but they are not alive. They are just little pieces of some of the kinds of chemicals that make up cells, floating around loose. They can't eat, can't grow, and can't even reproduce by themselves. So that's number one: don't take it personally. They aren't out to get you. In fact, they aren't out to do anything. They're just really tiny little pieces of dead stuff that happen to mess up your body.

It's important to say that because lots of doctors and nurses and people who produce what they consider to be "educational" materials about HIV talk about the virus as though it's intelligent -- it can "outsmart" the drugs; it's malevolent -- the virus is like enemy soldiers and we need to keep our own soldiers in the field; and it's even drawn as an ugly monster with teeth and claws. It's nothing like that, all that is a load of crap and it isn't helping anybody understand anything.

So before we can understand what a virus really is we have to understand cells. We seem to be pretty solid -- we have lumps of stuff inside, such as muscles and our brain and our liver and so on, with blood flowing through tubes and what not and a solid fabric of skin stretched over the whole thing. But if we could shrink down to incredibly small size it would look completely different. It's all made out of cells, which are in the range of 30 millionths of a meter across, much too small to see although it's easy to see them with a microscope, and we have, get this, about 50 trillion of them, i.e. 50 times a million times a million. That's a lot.

You usually see complicated pictures of them, but I'm going to start off really simply. The cell is actually three dimensional, of course. They can be just about any shape but we'll imagine that this one is more or less spherical, and I've cut it in half so we're looking at a cross section. It's a membrane filled with a fluid. The fluid is called the cytoplasm, in case you want to build up your vocabulary, but that's not important, it could be called anything. For now, I'm not showing anything of what's inside, I'm just showing the outside.

You'll notice in my highly artistic drawing that there are a bunch of things sticking through the membrane. These are molecules called proteins. There are all kinds of different proteins and they perform many different functions in cells. These proteins let specific kinds of things in and out of the cell, or actively move them in and out. Some small molecules, such as gases, can move through the membrane on their own, but for the most part these proteins control what goes in and out.

Next time: More about proteins.


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