The human genome is a string that runs the length of a football field. All the genes that encode protein are at the ends. You are now able to take two major steps forward. All the information about protein is behind you.
Three billion base pairs make up the human genome, but only 2% encode proteins. The remainder seems like pointless bloat with a profusion sequence duplications, genomic dead ends and genomic dead end often called junk DNA.
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There are many mysteries surrounding the question of noncoding DNA and whether or not it is valuable junk. It has been shown to be essential biologically for at least a portion of its contents. Researchers are now beginning to understand how non-coding DNA can be used as a gene resource and nursery for new genes.
Slowly, slowly and slowly, junk DNA terminology [has] begun to die," said Cristina Sisu (a geneticist at Brunel university London).
Although scientists have casually used the term junk DNA since the 1960s, the evolutionary biologist Susumu Ohno first coined it in 1972 to suggest that large genomes would undoubtedly contain sequences that were passively accumulated over many centuries and that did not encode proteins. Researchers soon found hard evidence that this junk DNA is abundant in genomes and its varied origins. They also discovered how much of it is transcribed to RNA, despite not having the blueprints for protein genes.
Sisu stated that technological advances in sequencing have made it possible to change the way scientists view non-coding DNA andRNA. These noncoding sequences don't carry any protein information but are often shaped by evolution to achieve different ends. The functions of various junkinsofar that they have functions are becoming clearer.
Some of the non-coding DNA in cells is used to create a variety of RNA molecules that regulate and assist protein production. These molecules include small nuclear RNAs as well as microRNAs. There are many more. Some have short segments that are typically shorter than two dozen base pair length, while others can be an order of magnitude longer. Some are double-stranded or fold in on themselves in hairpin loops. All of them can be selectively bound to a target (e.g., a messengerRNA transcript) to promote or inhibit its translation to protein.
These RNAs have a significant impact on an organism's well-being. For example, experiments with mice that shut down certain microRNAs have caused disorders such as tremors and liver dysfunction.
Transposons are segments of DNA that have the ability to change their position within a genome, which is the largest category of non-coding DNA found in human genomes and other organisms. According to Seth Cheetham (a geneticist from the University of Queensland, Australia), these jumping genes are prone to making many copies of themselves, sometimes hundreds of thousands. Retrotransposons are most prolific. They spread quickly by creating RNA copies of their own that then convert to DNA in another part of the genome. Transposons make up about half of the human genome. In some maize plants that number rises to around 90 percent.
Noncoding DNA can also be found in human and other eukaryotes' genes. It is located in the intron sequences, which interrupt the protein-encoding exon sequences. The exon RNA from genes is spliced together to make mRNAs. However, much of the intron DNA is discarded. Some intron RNA may be converted into small RNAs, which are important for protein production. Although it is not clear why eukaryotes have them, researchers believe that they help speed up gene evolution by making exons more accessible for reshuffle into new combinations.
