The central dogma of genetics used to go something like this: Our genes (DNA) are transcribed into smaller pieces (RNA), which are then translated into the proteins that build our body.
Now it's looking like that old dogma just won't hunt. (Apologies for a bad pun at the expense of the scientific method, that great, messy, wonderful process -- just like democracy!)
Previously, scientists thought each of our genes acted as a blueprint for a single protein. Then they discovered that single genes may be alternatively spliced into different RNA transcripts, resulting in different proteins from the same gene. But they still claimed that only 5% of our genetic material was being used to encode for proteins, and the other 95% of the gene was snipped out in the transcription process, relegated to the cutting room floor as junk DNA.
Recently, however, a group of scientists comprising the ENCODE project decided to look more deeply into this puzzle, by examining 1% of our DNA in more detail. And they found clues for what the other 95% of our DNA does.
According to Thomas D. Tullius, professor of chemistry at Boston University and one of the ENCODE researchers
"There were huge surprises; this research has upset a lot of thinking about how the genome works." ... "There now appear to be thousands of places in the genome that were long thought to be useless or meaningless [junk DNA], but which we now see to have a functional role. But we don't really understand what that role is."
Other interesting findings:
The new work suggests that the "control regions" in the DNA are far more extensive, perhaps embracing more than half of all DNA. Functions thought to be carried out by genes alone now appear to be managed by multiple, overlapping segments of DNA. In addition, other portions of the genome are believed to be on standby, as a toolbag to be utilized as humans evolve.
The ENCODE project found that much of our DNA doesn't code for proteins at all, but instead is transcribed into specialized microRNA molecules that may be just as interesting as DNA and proteins. These are scnRNAs, snRNAs, snoRNAs, rasiRNAs, tasiRNAs, natsiRNAs and piRNAs.
MicroRNAs seem to act as behind-the-scenes puppetmasters, helping to regulate protein activity. For example
Dave Bartel, of the Massachusetts Institute of Technology ... discovered microRNA genes interspersed among sets of protein-encoding genes called Hox clusters. Hox clusters contain basic instructions about body plans, and the genes within them are arranged in the order in which they influence their owner's shape during development. In short, a Hox gene at one end of a cluster contains the information: “Give this embryo a head”. The gene at the other end says: “And a tail, too”. The role of the interspersed microRNAs is to regulate these high-level commands.
Ronald Plasterk, of the University of Utrecht, in the Netherlands, suggests that microRNAs are important in the evolution of the human brain. In December's Nature Genetics, he compared the microRNAs encoded by chimpanzee and human genomes. About 8% of the microRNAs that are expressed in the human brain were unique to it, much more than chance and the evolutionary distance between chimps and people would predict.
RNA also opens up a mechanism for Intelligent Design because:
small RNAs are active in cells' nuclei as well as in their outer reaches. Greg Hannon, of the Cold Spring Harbor Laboratory in New York State, thinks that some of these RNA molecules are helping to direct subtle chemical modifications to DNA. ... They thus change the effective composition of the genome in a way similar to mutation of the DNA itself (it is such mutations that are the raw material of natural selection)....
RNA could itself provide an alternative evolutionary substrate. That is because RNA sometimes carries genetic information down the generations independently of DNA, by hitching a lift in the sex cells.
