Scientists once considered certain parts of our genome “junk DNA,” since it didn’t produce proteins – the molecules essential to cells – as “junk.” But recently, researchers reported that some of this junk DNA now produces proteins; perhaps helping shape our extraordinary brainpower?
What is Junk DNA?
Junk DNA refers to parts of an individual’s genome that do not encode for proteins. Although the term is sometimes applied incorrectly, junk does not indicate their non-importance; rather it refers to their lack of scientific interest. Researchers had long noted the absence of proteins from large portions of our human genome – it wasn’t until the Human Genome Project recorded the coding regions that they realized how much “junk DNA” there actually was.
Protein-coding genes work by writing their genetic blueprint into an RNA molecule before sending it directly to a machine that manufactures proteins – the ribosome. While some of this RNA may be discarded after being synthesized into components for other cell machines, others become what’s referred to as junk DNA – leaving only some for production within cells themselves.
Scientists are discovering increasingly useful functions for noncoding regions of DNA that were once considered junk, such as one supposedly useless section that now regulates sperm production by controlling its gene. Another noncoding region known as an intergenic region may play an integral part in blood cell formation while yet another plays an intergenic role by helping cells repair damaged DNA.
This discovery that noncoding regions have developed functional roles is an eye-opener to anyone who believes noncoding DNA segments to be insignificant, though the discussion is far from over; one must remember that any DNA segment can only qualify as functional if it meets four criteria:
(1) does it contribute positively to fitness, (2) did it arise through adaptive processes, or (3) does it improve an existing trait’s function? Until we know the answers to these questions, it would be prudent not to dismiss any region of our genome as junk.
Why is Junk DNA important?
Genetic material commonly known as junk DNA plays an essential part in our genomes even though it doesn’t code for proteins directly. Scientists have long been confused by this seemingly useless genetic material that dominates so much of the genome; they don’t understand why nature would force their genome to carry so much extra baggage.
Recent discoveries by researchers indicate that much of this non-coding genetic material plays an essential role in evolution and survival of organisms. UCSD biologist Peter Andolfatto and his colleagues recently published the results of their research in Nature journal showing how non-coding regions play an essential part in gene regulation.
Horizontal gene transfer (HGT), when segments of DNA that do not correspond to any genes are transferred between cells during cell division, occurs. Sometimes this sequence becomes part of new cells while in other cases it accumulates as “junk DNA”.
Junk DNA may be used to produce non-coding RNA molecules such as transfer and regulatory RNA. Furthermore, some junk DNA plays an integral part in transcription – the process by which genes are read and turned into proteins.
Junk DNA has also been associated with cancer, an illness in which abnormal cell division results in cancerous lumps to form. A study published in Annals of Oncology discovered that variations to specific junk DNA sequences increase risk for breast and prostate cancer development.
Studies have also demonstrated that variants in junk DNA may be linked to other diseases, including cardiovascular disease and type 2 diabetes. These results demonstrate the prevalence of variation in junk DNA beyond what had previously been thought; polygenic risk scores that consider thousands or millions of variants across the genome may help identify people at greater risk for diseases; it remains unclear as to why some variants increase risk while others do not.
How does Junk DNA work?
Junk DNA refers to regions of genetic material that do not code for proteins. Although these regions don’t contribute directly to one’s physical characteristics or protein makeup, they still play an essential part in maintaining optimal cell functioning and play an essential part in helping us live life fully and freely.
Scientists previously thought noncoding DNA, known as junk DNA, served no real function within an organism’s genome. According to a new study published in Nature journal, junk DNA may actually play an essential part in maintaining good genome health in an organism.
Researchers examined genomes from various species of bacteria and fungi and discovered that noncoding DNA does indeed serve specific functions. Some examples include producing RNA molecules used in cell proteins; binding transcription factors; controlling gene expression; as well as helping control expression of genes through transcription. It’s believed that much of our junk dna may also serve these purposes in human genomes.
These findings indicate that while genes are the core component of our genomes, junk dna plays an equally critical role in gene regulation and overall function. While geneticists used to focus on finding individual genes with associated proteins, the reality of our genomes may be much more complex.
Scientists have long understood that most of the human genome contains noncoding DNA. What remains unknown, however, is how each type of noncoding DNA functions; while ENCODE project has provided some clues into this mystery it remains largely unclear how these pieces of genome interact to regulate gene expression or promote or suppress certain biological processes.
One research team at UCSD recently discovered that noncoding DNA could act as a buffer against functional parts of their genome by speeding up decay of precursor ribosomal RNA produced when genes are converted to mRNA – marking the first time noncoding DNA played an instrumental role in gene regulation.
What are the implications of Junk DNA?
Researchers long believed that junk DNA served no functional purpose, since it did not get transcribed into RNA and contribute to producing proteins. But recent research has demonstrated that certain regions do indeed influence gene expression – suggesting junk DNA may have greater impacts on organism phenotype than previously assumed. This discovery has profoundly altered scientists’ views of genes and genomes.
Scientists have long known that most of the genome does not encode for protein-coding DNA, yet its role remained unclear. Thanks to ENCODE project, scientists now understand what role non-coding regions have; many do in fact regulate gene expression!
Some non-coding regions contain genes used to make non-translatable RNA molecules that act as regulators, turning up or down expression of genes like turning up or down volume on your radio.
An important discovery has been that non-coding regions can often affect gene regulation without altering its core code, since these regions do not get translated directly into proteins but rather other RNA molecules like transfer and ribosomal RNA that then get processed by cells into proteins – although sometimes mutations of junk DNA disrupt this processing, leading to diseases like cancer.
Furthermore, much of the genome contains “wild-type” (“WT”) sequences which do not correspond with any protein-coding genes and are often referred to as “junk DNA”. Recent research has demonstrated how natural selection may reassign some of these sequences to new functions such as regulating transcription or aiding RNA degradation.
However, it should be borne in mind that junk DNA has less functional significance than coding DNA due to mutations not typically impacting phenotypes and being therefore unlikely to be selected against. Furthermore, many of its functions do not appear significant to evolution.
