Some of you readers out there may have heard the term “Junk DNA” tossed around a few times or mentioned in a periodical recently. It is one of the new big hypes in modern genetics, and there has been a lot of debate within the scientific community as to the extent of how much of an organism’s genome is actually “junk”, and how much of the noncoding DNA still serves a useful purpose for the organism.
First, I must note that I’ve changed positions on this matter to some degree. I used to think that the idea of 80% of the human genome being not only noncoding DNA but also just flat-out useless was complete nonsense. As is a common occurrence in scientific innovation, however, my narrow-minded stance has been obliterated by further investigation into the matter. Though, for the record, I’m still not a fan of Richard Dawkins (a big proponent of “junk” DNA theories), but that is due to matters not related to the pursuit of science and understanding.
Second, despite my change in stance, I still despise the term “junk DNA”. It’s overly simplistic and makes all noncoding DNA sound utterly useless, which is far from the truth. There are, however, vast segments of eukaryotic DNA (eukaryotic being the cell types of multicellular organisms) that are basically prehistoric leftovers that were deactivated from protein expression, as well as the occasional endogenous retrovirus fragment that was never expressed to cause an infection and therefore got to stick around in the organism’s DNA as said organism made offspring for generations to come.
A brief explanation of how DNA is expressed to yield blue eyes, a leaf, a snout, etc etc. DNA is not directly used for the piecing together of cellular proteins that give rise to the larger structures on an organism. What happens is a section of DNA is pulled apart (usually due to some intracellular or extracellular signal) and a single-strand of correlating RNA is synthesized then released into the cellular fluid. An RNA strand is simply like a half-strand of a segment of DNA that floats around in the cell. Proteins that are ingested into the cell then line up with their respective base-pairs on the floating RNA strands, which are then released from the RNA once all the proteins have assembled and bonded alongside one another. These assembled proteins serve as the basic building blocks for an organism’s overall structure. There are more intricate details to the process, but this is the gist that is needed to understand what junk DNA really is all about. Oh, and from now on, I will be using the term “noncoding DNA” in the article. Below are my reasons.
A lot of noncoding DNA is an evolutionary adaptation that helps protect against mutations, particularly in complex organisms. DNA base pairs are “read”, if you will, in groups of three (three base pairs code for a particular kind of protein). If one of these base-pairs is deleted, or an extra is inserted, it would throw off the entire order of proteins that all subsequent base-pairs were supposed to encode for, if not for these long segments of unexpressed material. These long segments of “junk” assure that the deletion/insertion is isolated to only one particular region on the DNA instead of the whole strand.
Introns are also valuable pieces of noncoding DNA. Introns are parts of the RNA strands that are “chopped out” of the RNA strands so the encoding portions of the strand can be recombined differently. This allows for a single segment of DNA to have the capacity to create multiple different RNA strands, and therefore build multiple protein structures, which greatly increases the >efficiency< of a segment of DNA. So, the term “junk DNA” that is used to refer to all noncoding DNA is a nasty misnomer. Some noncoding DNA serves no purpose for the organism, some does.
There are more kinds of noncoding DNA that are still vital to cell function, but I will not describe all of them. I will, however, explain what exactly the big deal over junk DNA really is about.
So I decided to do a bit of digging on websites like livescience.com and everyone’s beloved Wikipedia. I found these: http://www.livescience.com/31939-junk-dna-mystery-solved.html
On the wiki page, scroll down to the “Functions of Noncoding DNA Sequences” section and look at the first paragraph. “Linkage mapping often identifies chromosomal regions associated with a disease with no evidence of functional coding variants of genes within the region, suggesting that disease-causing genetic variants lie in the noncoding DNA.”
I don’t think you even have to know what linkage mapping is or what chromosomal regions are to grasp the importance of this little sentence here. Disease-causing genetic variants, lie, in, the, noncoding DNA: the real junk DNA of the “junk DNA”. This is huge. Yet I had to go digging to find this. It is never properly explained in the average article. It is usually, and falsely, implied that functionless noncoding DNA CAN function, but simply has been shut off to remain unused, and sometimes holds disease-causing genes that would show up in a genetic test despite the gene not being expressed.
Junk DNA is being investigated so thoroughly because it one of the likely possible sources for faulty genetic material that is expressed and results in disease and disorders. It makes sense too, that it would be, once you get the real scoop on our so called useless DNA, especially when one considers the mutation buffer type of noncoding DNA. If a part of this “mutation” buffer was to inadvertently get expressed, it is likely that a faulty gene would be expressed and results in disease. After all, the material that is essentially supposed to be screwed up is being expressed.
It would therefore be of great benefit to find a way to rid the human genome of the non-functional, disease causing noncoding DNA.
So, don’t let the term “junk” DNA give all noncoding DNA a bad rap. I’ll do the scientific community a favor here and promote the more accurate explanation. Junk DNA is referring to the prehistoric and degraded genetic leftovers within noncoding DNA that cause us a lot of headache by resulting in diseases.