In 1972, the geneticist Susumu Ohno formalized the term “junk DNA” to describe DNA that do not encode protein sequences or non-coding DNA.
In 2000, scientists presented the Human Genome Project confirming that around 98% of the human genome had no apparent function. Therefore, only about 2 percent of DNA is made up of protein-coding gene
What are the functions of non-coding DNA?
Humans contain almost 3.5 billion nucleotides packaged in 23 pairs of chromosomes and for decades and, until recently, most non-coding DNA or “junk” DNA has been believed to have no specific function.
However, over the years, different studies described that some non-coding DNA sequences may provide some form of functional activity, affecting the expression levels of certain genes. Among these sequences we can find:
- Promoters providing binding sites for the protein machinery that carries out transcription
- Enhancers providing binding sites for proteins that help activate transcription
- Insulators providing binding sites for proteins that control transcription
- Silencers providing binding sites for proteins that repress transcription
In other words, non-coding DNA is very important for turning genes on and off. Therefore, scientist think that the phrase “junk” DNA should be retired, as its implications may have delayed interest and research in the biological functions of non-coding DNA.
Other non-coding DNA sequences correspond to structural elements, including repeated sequences forming the ends of chromosomes or telomeres, protecting the chromosomes from being degraded during replication. In additions, some non-coding sequences are frequently used for purposes of forensic identification to identify a person.
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