[chimera (OP)]

One of the paradigms of modern biology is that DNA and RNA are the code of life, popularly put.

This would seem to indicate that an important function of general coding is maintained, namely that one code produces one result. Always nice if you know what to expect.

Now I read this article about how eyes form, and a little tidbit of information caught my eye, and since it was not the major issue of the article, it was not embarked upon in great detail, but my attention was piqued:

it seems there is a protein in the eye of a duck, that is a kind of opaque glittery affair, with some clear-cut function. That is not it's salient property to me, though, but more the fact that the piece of DNA in the ducks' liver I believe, that creates that protein, already was known to create an altogether entirely different protein, which undoubtedly has some interesting function elsewhere, but that is not the point: how can the system decide when it should do what if DNA/RNA contains all code?

Errrm... are people aware of this phenomenon in other places? What could be the mechanism? Does this have any other consequences we should be aware of?

(Haven't got the article at hand, unfortunately, but if people have any doubts as to the story, I'll go digging...)

[anthony]

After the sequencing of the human genome it was determined there were 30,000 human genes. This is far smaller than the size of the human "proteome" - ie the library of proteins/enzymes in the human species. Probably each gene codes for 10 proteins, so 300,000 proteins is a good guess. The human genome was easy to sequence, and the technology was readily available, however, this is not the case for the proteome at the moment. Genes cover only a tiny proportion of DNA in the cell, about 5%, genes are easily recognised by their "START HERE" and "STOP HERE" instructions in the code. The rest of the DNA isn't so easily understood and has many functions and has the historical title of "junk DNA".

So there are 30,000 genes, 300,000 proteins and around 2^300,000 possible interactions between proteins, this is where the true complexity of biology lies, not in DNA. It's rather like the game of "Go" with those white and black counters arrnaged on a grid. The instructions for play are incredibly simple, however play is incredibly complex, determining the games popularity in maths departments worldwide.

To answer your question once a protein is copied from the code it then interacts with other proteins and can be modified. Either shortened, tacked onto another protein, covered in sugars, given a metal ion, loosing a metal ion, coated in lipids, whatever. All this through interaction with other proteins. A cell knows what type of cell it is through the balance of proteins within it and it maintains it's condition once it's set, and this will determine what genes are read within the cell and what happens to the proteins that are read from them.

So it's true DNA is the code of life, but it cannot control each object it encodes, each object is freely interacting with everything else about it, and as I desribed earlier this makes biology incredibly complex. Much more complex than physics.