RNA - Phew
In the news of recent weeks is a sudden upsurge of interest in RNA. The Economist had a lengthy article on it. My reaction to the whole surge is "At last they have found it". Since they sequenced the Human Genome, and found only 30,000 genes, or possibly even before then, I have felt that there was something missing in the basic story of how cells are built and maintained. Just as cosmologists have needed Dark Matter to stop galaxies flying appart, and Dark Energy to keep the universe flying apart, as both are observed to do, I felt that there was some Dark Information needed to make cells work. And now it has been found.
The dogma for the last 50 years is that the working parts of the DNA, called genes, code for a particular kind of RNA, which in turn constructs a particualr protein. 1 gene coded for 1 protein, though that protein may have several uses, and the gene may be turned on or off at different times and in different ways. So far so plausible - except the number of genenes seems to me to be much to small for the complexity of body built, and worringly constant despite the complexity of the animal constructrd. The flatworm Planaria, 1100-odd cells whose function has been mapped in great detail, has 20,000 genes to our 30,000. Is all the extra complexity of vertebrates, primates, and humans expressed in only 30,000 genes? Seems rather improbable to me.
So what, other than genes, is there in the DNA? Them genes form less than 10% of the total length of the chromosomes. A few other bits have identified uses, like the telomeres, the "endcaps" of the chromosome. But the rest was called "Junk DNA" and was widely believed not to code for anything. Various reasons were proposed for the Junk DNA - pure accident, stops useful genes getting destroyed during meiosis, raw material for new genes, remains of invading viruses. But it was believed it didn't do anything - it did not do the basic job of DNA, which is to be transcribes into RNA.
And now it transpires that it is transcribed into RNA - lots of kinds of RNA. Just not the kinds of RNA that build proteins. But they seem to do lots of other things, perhaps more directly than the protein coding ones. Genes that throw switches, rather than genes that build the machines with the switches. So suddenly we have a source of much more variation to explain the variety of life - and of people.
Phew.
The dogma for the last 50 years is that the working parts of the DNA, called genes, code for a particular kind of RNA, which in turn constructs a particualr protein. 1 gene coded for 1 protein, though that protein may have several uses, and the gene may be turned on or off at different times and in different ways. So far so plausible - except the number of genenes seems to me to be much to small for the complexity of body built, and worringly constant despite the complexity of the animal constructrd. The flatworm Planaria, 1100-odd cells whose function has been mapped in great detail, has 20,000 genes to our 30,000. Is all the extra complexity of vertebrates, primates, and humans expressed in only 30,000 genes? Seems rather improbable to me.
So what, other than genes, is there in the DNA? Them genes form less than 10% of the total length of the chromosomes. A few other bits have identified uses, like the telomeres, the "endcaps" of the chromosome. But the rest was called "Junk DNA" and was widely believed not to code for anything. Various reasons were proposed for the Junk DNA - pure accident, stops useful genes getting destroyed during meiosis, raw material for new genes, remains of invading viruses. But it was believed it didn't do anything - it did not do the basic job of DNA, which is to be transcribes into RNA.
And now it transpires that it is transcribed into RNA - lots of kinds of RNA. Just not the kinds of RNA that build proteins. But they seem to do lots of other things, perhaps more directly than the protein coding ones. Genes that throw switches, rather than genes that build the machines with the switches. So suddenly we have a source of much more variation to explain the variety of life - and of people.
Phew.