A representation of the spliceosome, a mollecular machine that performs some rather spectacular RNA cutting jobs. For a 3D view, go here.
An Outdated Dogma
DNA makes RNA makes Protein make Us used to be the central dogma of genetics and molecular biology. During the first few decades after the discovery of DNA and RNA, it was thought by most experts that the sole purpose of DNA was to code for proteins. In this context, it was quite surprising to find that only a small portion (about 2%) of the human DNA was actually doing that. In the early '70s, a biologist by the name of Susumu Ohno wondered why there appeared to by so much "junk" in our genome, and thus the term "junk DNA" came into existence (though some previous similar use of the term has also been reported).
Within an evolutionary framework, "junk DNA" was hailed as confirmation that we carry a lot of genetic baggage from our evolutionary ancestors, and it was postulated to be THE playground for mutations. Or, to quote Richard Dawkins, "junk" DNA was simply "a parasite, or at best a harmless but useless passenger, hitchhiking a ride in survival" (1976).
Although there were some scientists that theorized that it takes more than transcribing DNA and generating a bunch of proteins to make an organism as complex as a human, the research opportunities to look at the supposedly "junk DNA" were inhibited by the evolutionary paradigm cited above for more than 2 decades. After all, who wants to spend precious research money studying junk?
Treasure Hidden In Junk
During the last decade or so, though, a mountain of evidence has accumulated indicating not only that the vast majority of DNA is transcribed (over 90% according to most recent estimates), but also that a significant portion of what used to be called "junk" DNA plays crucial roles in regulating the 2% DNA that codes for protein.
Evolutionists are in a real state of panic over these developments, with some fanatical evolutionary scientists going as far as to try to dismiss the whole ENCODE project as worthless. Unfortunately for them, the data supporting its findings continues to accumulate.
Amazing Molecular Machines
I am digressing, though. Let's return to the central dogma of genetics: it is no longer true. Why? Enter the spliceosome, the transcribed RNA splicing molecular machine. Today we know that RNA undergoes quite a bit of post-transcription processing, before it is translated into protein(s). It is not unusual for a string of RNA to experience several splicing events, for example, during which several segments of various lengths (called introns) are removed. In addition, editing of certain nucleotide elements is performed, so the final RNA can look quite different than the DNA from which it originated.
Here is an animation of the RNA splicing process.
Why would cells spend precious energy to post-process transcribed RNA?
Not all the answers are in, but this process is an elegant way to generate variety in the final product (protein). In one extreme case, a Drosophila (fruit fly) gene produces as many as 38,000 different proteins from a single gene through alternative splicing. Another reason is efficiency; by generating multiple proteins from the same nascent RNA molecule, a one-to-many relationship is generated, which allows for a lot of flexibility.
While we'll never find an unequivocal "Made by God" inscription anywhere in the genome, the beauty of engineering simple solutions amidst such complexity is obvious when one looks at these processes, even at the limited level at which we currently understand them.