| | | The Meaning: Mysterious Proteins |
If DNA is a language, it is a language where the word meanings depend on their location, where words overlap one another, and where the meaning of words depends on long strings of modifiers that may not happen to be near the modified word. But human minds have decoded messy codes before. Perhaps we will make progress on this one, too.
Science has learned how to tease out some of the meanings in the language of your genes. We can examine some of the proteins certain genes build. We can correlate some genetic changes with changes in an organism. But is this the same as decoding the language? Suppose you spoke no English, and could not read this book. You show the book to a friend who can read English, and ask her opinion of it. Now you start changing single words here and there and asking her to reread the whole thing and tell you about the changes. Some changes she might not notice, while others would be more obvious. Some words are important to the sense of the book, but some aren't. (Like this one: "purple.")
When you change a word and it has an effect on your friend, you do know something, but maybe not much. For one thing, you have no way really to know whether the word you've removed was the important one, or perhaps it was the one you've added. You could change words in parentheses to anything you want, and not affect the overall meaning. What could you conclude from that? I could even write sentences that only make sense with nonsense words: "`Bfstplk' is unpronouncable." What will you learn when you experiment with substitutes for that word?
Faced with the task of translating a book in a foreign language, finding the letters and the words is the easy part. The hard part is deciphering the meaning behind the words. And it's even harder when the only method at hand is to substitute other words and see what happens. But that's roughly the way scientists are proceeding to "decode" the meaning of our genes. You might find the protein produced by some stretch of DNA, but proteins don't come with labels for their use. They are big ugly complicated molecules, and the only way to figure out their purpose is somehow to catch them in action. Even then, you don't always know if the function you've observed is the only thing they're good for. People spend entire careers studying a small handful of proteins, and there are hundreds of thousands of them to figure out.
To make matters worse, it turns out that many genes are redundant, or don't seem to matter that much. That is, when scientists try to figure out what is going on by knocking out or mutating some gene, they often find that there is no effect at all. (Or that the effect is not detectable in the adult animal.) It may be that many genes are actually redundant, but it may also be that a lot of genes may not code for a specific thing, and work in combination with many others, creating a kind of effective redundancy. That is, there may be no other source of some protein that a mutation has modified, but that protein may itself not be a particularly crucial ingredient, it may only change things slightly, too subtly to be detected by our experimental design, or it may be readily replaced by some other gene product. Some of these problems may also be due to interference by the DNA-restoring mechanism of the cell.
This is not to belittle the enormous work already done in reading the genetic code, nor the tremendous medical advances made possible by that work. But the fact remains that in the attempt to understand how organisms make themselves, "reading" the genome--figuring out what parts code for what proteins--is but a very small first step. When we know what protein is made by every single part of your DNA, and what each one is for, we still won't have the slightest idea how to make another one of you.
| | | The Meaning: Mysterious Proteins |