Evolution and complexity

I think that the bacterial genome is about 4.3 million base pairs and the human genome about 300 million, but don't quote me on that!!! The point is that even organisms as small and "simple" as bacteria have oodles of DNA. They maximise this by having no introns (non-coding regions) like eukaryotic cells have and also have a "dual coding system" whereby a gene read in one frame codes for one protein and read in a different frame, or read backwards, codes for another protein. In eukaryotes each gene is interspersed with introns and this information has to be spliced out before the final protein can be assembled. Additionally, each gene codes only for a single protein and can only be read in one frame - there is no equivalent of the "dual coding system". On the face of it, this makes the system used by bacteria seem much more complex and sophisticated than that used by what we consider to be more advanced organisms. Does this help?

I don't think I made this clear enough. When I said the dual coding system means that a bit of DNA can code for one protein in one direction and another in the other direction etc what I should have added is that BOTH PROTEINS ARE VITAL TO THE CELL. The coding system carries all the info needed for a cell to make the proteins it needs - it's a sort of architect's blueprint. The code tells the protein synthesis machinery which amino acid to add next to the growing amino acid chain (proteins are built from amino acids). The order of theamino acids in the chain and any modifications that then take place determine the properties of the protein. Without the code in the DNA in the first place the protein can't be made.If you consider how the code actually works you realise how difficult it is to use a single sequence of DNA to code for more than one protein. The code is carried by four bases called A, C, G and T and the order they come in determines the amino acid sequence. However, it's not as simple as that as it takes three bases together to code for a single amino acid. For example ATG codes for methionine at the start of the protein. For the full genetic code check out this site http://www.users.rcn.com/...ranet/BiologyPages/C/Codons.html From this you can see that it's quite a complicated task to manage to work out how to code for two different proteins using a single stretch of bases.

No is the short answer. Trying not to stray off topic, all I wanted to show was that complexity can be a difficult thing to define and can depend on what bits of an organism you're considering, or what processes.By the way, Ned, stilltrying to dig out the rats and warfarin stuff for you.

By vital I mean essential to life. Without the protein the cell will die. I'm not talking about complexity as in the NUMBER of proteins produced - I'm talking about having a system which incorporates this ability to code for two essential proteins on a single sequence of DNA.In general only a single strand of the double stranded DNA codes for proteins - the sense strand. It's complementary strand, the antisense strand isn't used (for this you have to know that A on the sense strand is T on the antisense strand, C is G, G is C and T is A). This dual coding system is able to use the antisense strand to code for proteins as well as the sense strand, but not only that, it uses a part of the antisense strand that complements a coding region on the sense strand.I'm emphasising this on a particular level to illustrate that complexity is a subjective quantity - it depends on who's doing the looking and what they're looking at.Sorry about the error in the link, I gather you found it.

I know of this system in viruses and bacteria, I'm not aware of any overlapping genes in "higher" organisms including humans, yet I think you would agree that normally humans etc would be considered more complex than bacteria and viruses. For example, most potato viruses have a grand total of 8-10 genes, humans have approx 30,000 genes. Yet the DNA coding system used by the viruses and bacteria can "seem" so much more complex when compared to the system in humans who have oodles of non-coding DNA and pseudogenes. That's the only point I'm trying to make.