human imagination The genome is like a string that runs the length of a football field, with all the genes that encode proteins clustered at the ends near your feet. Take two big steps forward; All protein information behind you now.
The human genome contains three billion base pairs in its DNA, but only about 2 percent of them encode proteins. The rest looks like useless bloat, an abundance of repeat sequences and genetic dead ends often called “junk DNA”. This astounding assignment of genetic material is not limited to humans: even many bacteria seem to allocate 20 percent of their genome to non-coding fillers.
Many mysteries still surround the question of what non-coding DNA is, and whether it is really worthless junk or something else. Parts of it, at least, have been shown to be of vital biological interest. But even beyond the question of its function (or lack of it), researchers are beginning to appreciate how non-coding DNA can be a genetic resource for cells and a nursery in which new genes can evolve.
Slowly, slowly, slowly, the terms ‘junk DNA’ [has] began to die” Christina Sisso, a geneticist at Brunel University London.
Scientists have casually referred to “junk DNA” since the 1960s, but used the term more formally in 1972, when geneticist and evolutionary biologist Susumu Ono used it to say that large genomes would inevitably harbor sequences, negatively accumulating over many thousands of years. No proteins were encoded. Shortly thereafter, the researchers obtained compelling evidence of how abundant this scrap is in the genome, how diverse its origins are, and how much it is transcribed into RNA despite its lack of proteomics blueprints.
Technological advances in sequencing, particularly in the past two decades, Sisso said, have greatly changed the way scientists think about RNA and non-coding DNA. Although these non-coding sequences do not carry proteomic information, they are sometimes formed by evolution to different ends. As a result, the functions of the various classes of “junk” – insofar as they contain functionality – are becoming more and more clear.
Cells use some of their non-coding DNA to create a variety of RNA molecules that regulate or aid protein production in different ways. The catalog of these molecules continues to expand, with small nuclear RNAAnd Micro RNAAnd intertwined little rna And much more. Some are short segments, usually less than twenty base pairs long, while others are an order of magnitude longer. Some are double stranded or folded into hairpin rings. But each can selectively bind to a target, such as a messenger RNA transcript, to either enhance or prevent its translation into a protein.
This RNA can have significant effects on an organism’s well-being. Experimental shutdowns of some microRNAs in mice, for example, have resulted in disturbances ranging from shivering to me Liver weakness.
By far the largest class of non-coding DNA forms in the genomes of humans and many other organisms transposons, segments of DNA that can change their location within the genome. These “jumping genes” have a tendency to make many copies of themselves — sometimes hundreds of thousands — across the genome, he says. Seth CheethamA geneticist at the University of Queensland in Australia. The most prolific is Inverse transposons, which spread efficiently by making copies of RNA of itself that are transformed back into DNA elsewhere in the genome. About Half of the human genome is made up of transposons; In some corn plants, this figure rises to about 90 percent.
Non-coding DNA also appears within the genes of humans and other eukaryotes (organisms with complex cells) in intron sequences that interrupt protein-coding exon sequences. When genes are transcribed, exon RNA is cleaved together into mRNAs, while much of the intron RNA is discarded. But some of the intron RNA can be turned into small RNAs participate in protein production. Why eukaryotes have introns is an open question, but researchers suspect that introns help speed up gene evolution by facilitating the reshuffling of exons into new clusters.