The Complex Truth About ‘Junk DNA’


Think of the man the genome is like a string stretched for the length of a football field, with all the genes encoding the proteins accumulated at the end near your feet. Take two big steps forward; all the protein information is behind you.

The human genome has three billion base pairs in its DNA, but only about 2 percent of them encode proteins. The rest seems to be a useless blank, a plethora of sequences and dead genomic endings that are often marked as “junk DNA.” This surprising inability to allocate genetic material is not limited to humans: Even many such bacteria allocate 20 percent of their genome to non-coder filler.

Many mysteries still surround the issue of what is not DNA coding, and whether it is useless garbage or something else. Its components, at least, have become biologically important. Even if more on the question of its function (or lack thereof), researchers are beginning to appreciate how non-coding of DNA can be a genetic resource for cells and a nursery in which to change. or the new genes.

“Slowly, slowly, slowly, the terminology of‘ junk DNA ’ [has] began to die, ”he said Cristina Sisu, a geneticist at Brunel University London.

Scientists often referred to “junk DNA” as early as the 1960s, but they took this term more formally in 1972, when geneticist and evolutionary biologist Susumu Ohno used it to argue that large genomes were inevitably there are sequences, which have accumulated over many millennia, that do not encode any proteins. Soon after, researchers gained hard evidence of how much of this waste is in the genomes, how different its origins are, and how much RNA is transferred even in the absence of blueprints for proteins.

Advances in sequencing technology, especially over the past two decades, have done much to shift how scientists think about non-coding DNA and RNA, according to Sisu. Even if the irregular sequences do not carry protein information, they are sometimes molded by evolution at different ends. As a result, the functions of the different types of “garbage” – as they have functions – are becoming clearer.

Cells use some of their non-coding DNA to create a different menagerie of RNA molecules that control or help make protein in different ways. The catalog of these molecules continues to grow, with small nuclear RNAs, microRNAs, small disruptive RNAs and many more. Some are short, usually no less than two dozen base pairs in length, while others are an order of size. Some exist as double strands or fold back themselves into hair loop loops. However all of these can be selectively selected on a target, such as an RNA messenger transcript, to enhance or inhibit its translation into protein.

These RNAs can have many beneficial effects on an organism. Experiments that shutdown certain microRNAs in mice, for example, cause diseases from trembling on liver healing.

Currently the most common category of non-coding DNA is in the genomes of humans and many other organisms. transposons, parts of DNA that can change their location within a genome. These “jumping genes” have the nature to make multiple copies of themselves – sometimes hundreds of thousands – of the entire genome, as Seth Cheetham, a geneticist at the University of Queensland in Australia. The most productive retrotransposons, which are effectively propagated by making copies of RNA themselves that are reverted to DNA elsewhere in the genome. About half of the human genome is composed of transposons; in some corn crops, that increase is nearly 90 percent.

Noncoding DNA also shows up in the genes of humans and other eukaryotes (organisms with complex cells) in intron sequences that interfere with protein encoding sequences. When genes are transferred, exon RNA is combined to bind to mRNAs, while most of the intron RNA is discarded. But some of the intron RNA can turn into small RNAs that are apil sa making protein. Why eukaryotes have introns is an open question, but researchers suspect that introns can help speed gene evolution by making it easier for exons to reproduce in new ones. combination.



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