Complex truths about ‘junk DNA’

Imagine people The genome as a string stretched for the length of a football field, with all the genes encoding the proteins clustered around your feet. Take two big steps forward; All the protein information is behind you now.

There are three billion base pairs in the DNA of the human genome, but only 2 percent of them encode proteins. The rest seems like meaningless lungs, a trend of sequential counterfeiting and genomic dead ends often labeled “junk DNA”. This strangely frugal allocation of genetic material is not limited to humans: even many bacteria seem to be engaged in 20 percent of their genomes in noncoding fillers.

There is still a lot of mystery surrounding what noncoding DNA is, and whether it’s really worthless garbage or something else. Parts of it, at least, have become biologically important. But beyond questioning its effectiveness (or lack thereof), researchers are beginning to appreciate how noncoding can be a genetic resource for DNA cells and a nursery where new genes can evolve.

“Slowly, slowly, slowly, slowly, the term‘ junk DNA ’ [has] Is starting to die, ”said Christina Sisu, a geneticist at Brunel University in London.

Scientists casually referred to “junk DNA” in the 1960s, but they adopted the term more formally in 1972, when geneticist and evolutionary biologist Susumu Ohno argued that large genomes would inevitably be disciplined, inactivated by many. Not any protein encoded. Soon after, researchers found solid evidence of how much of this waste is in genomes, how diverse its origins are, and how much of it has been replicated in RNA despite the lack of a blueprint for protein.

Sisu said technological advances in sequencing, especially over the past two decades, have done much to change the way scientists think about noncoding DNA and RNA. Although these noncoding sequences do not carry protein information, they are sometimes evolved to different ends. As a result, it is becoming clear that different classes of “junk” have functions such as cle.

Cells use some of their noncoding DNA to create a diverse manager of RNA molecules that regulate or assist protein production in a variety of ways. The catalog of these molecules is constantly expanding, with small nuclear RNAs, microRNAs, small interfering RNAs and much more. Some shorter parts, usually less than two dozen base pairs long, others longer dimension sequences. Some exist as double strands or fold themselves into hairpin loops. But each of them can be selectively bound to a target, such as a messenger RNA transcript, either to promote or prevent its translation into a protein.

These RNAs can have a significant effect on the well-being of an organism. For example, experimental shutdown of certain microRNAs in rats has caused disorders ranging from vibration to liver disease.

By far the largest division of noncoding DNA in the genomes of humans and many other organisms is transposition, the part of DNA that can change their position within a genome. Seth Chitam, a geneticist at the University of Queensland in Australia, said these “jumping genes” have a tendency to make many copies of themselves across the genome – sometimes in the thousands. The most effective is retrotranspiration, which is converted into DNA elsewhere in the genome and efficiently propagated by making its own RNA copy. About half of the human genome consists of transposons; In some corn plants, this number rises to about 90 percent.

Noncoding DNA is also found in the genes of humans and other eukaryotes (organisms with complex cells) that disrupt protein-encoding action sequences. When genes are copied, exon RNA splits into mRNA together, while many intron RNAs are discarded. But some intran RNA can turn into smaller RNAs that are involved in protein production. Why eukaryotes’ introns are an open question, but researchers suspect that extrons help accelerate gene evolution by making them easier to modify into new combinations.

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