• Question: Why does the human genome have so many non-coding regions? What is the purpose of them?

    Asked by anon-254948 to Laura, Faith on 21 May 2020.
    • Photo: Faith Davies

      Faith Davies answered on 21 May 2020:

      Just a few years ago all the non-coding regions were known as junk DNA, and mostly people didn’t they meant very much but that opinion has more or less disappeared I think now. There are all sorts of regions that don’t code for a protein but can, for instance, affect how much genes are expressed. I think the next few years we’ll discover more and more about what the non-coding bits do.

    • Photo: Laura Durrant

      Laura Durrant answered on 21 May 2020:

      Hi Mahek, this is a very interesting question! Unlike coding genes, ‘non-coding’ genes are regions of DNA that do not produce structural proteins and enzymes. In fact, scientists have shown that these non-coding regions contribute a whopping 98-98% of the human genome! For a long time, this was referred to as ‘junk DNA’ as it was assumed that these inherited regions were silenced as humans evolved.
      But what was discovered later turned this hypothesis on its head… in fact, scientists discovered that these regions encode for small molecules called ‘non-coding RNAs’. These are essential for regulating gene expression – that is, they can control which coding genes are switched ‘on’ and ‘off’ at any given time. This is a process called epigenetics, which is a huge area of interest for researchers. A hot topic at the moment is the role of these non-coding RNAs in regulating gene expression during development in the womb. Studying this process will help us understand congenital diseases on a genetic level and how we could intervene with medicine!

      I hope this answers your question 🙂 Here are is a link to a feature from Nature about this topic if you are interested in finding out more:
      https://www.nature.com/articles/538275a

Comments

  • Photo: Summer

    Summer commented on :

    Hey Mahek, great question!
    Non-coding regions were branded junk DNA for a long time and unimportant because they did not code for proteins. However, these non-coding regions have been shown vital regulatory elements, meaning they are capable of controling the coding regions. There are many caterogies non-coding regions can be put into. For example promoters which are binding sites for replication machinary that carry out transcription (the first step in creating proteins) and there are also silencers that are binding sites for proteins that stop transcription (stop the production of proteins).
    Other regions provide instructions for RNA molecules like miRNA, heres a great article about them https://theconversation.com/micrornas-the-junk-genetic-material-with-huge-potential-to-fight-cancer-and-dementia-133483. Really interestingly it has also been shown that lots of non-coding regions are capable of forming secret DNA structures, like the one I work on the i-motif and its sister the G-quadruplex.
    Non-coding regions are gaining more and more interest as their roles are being shown as vital for the correct amount of proteins being produced at the right times to make sure our cells function normally. Which also means that if a cell is in a diseased state the non-coding regions can play a major role in this and have been shown in many cases to. Making them powerful drug tragtes for diseases like cancers.

  • Photo: Nicole

    Nicole commented on :

    Hey Mahek!
    My two cents: I was involved in a study that looked at the genomes of lots of species of birds – some flightless, some not, to see which changes in the DNA occur during the evolution of different families of flightless birds. We found that one protein had changed in the flightless birds, but that didn’t explain much of their loss of flight. But, we saw the evolution of the same bits of noncoding DNA in our flightless birds, which changed when and where different genes were expressed. This made sense because genes that are expressed in birds wings to help them build muscle etc are also expressed in other parts of the body, so losing them would have consequences across the body while changing the noncoding regions in charge of expressing those genes during wing development wouldn’t cause the same collateral damage. This showed us that in complex organisms where the same gene is important for multiple traits, noncoding evolution can allow adaptation that a change in the protein couldn’t achieve.