#1302 What is junk DNA?

What is junk DNA? Junk DNA is DNA that doesn’t seem to do anything. It is not part of our coding DNA.

DNA is in the cell nucleus of all of our cells. DNA stands for deoxyribonucleic acid. The deoxyribo part is sugar. The nucleic acid part is a long chain like molecule. Inside the molecule are four of five possible chemical bases. These are adenine (A), guanine (G), cytosine (C), thymine (T), and uracil (U). There are about 3 million of these bases in our DNA and their order makes up all of our characteristics. 99% of our DNA is the same and the last 1% accounts for all of our differences, such as eye color, height, and so on. We inherit this DNA from our mother and our father, which is why we look so much like them, and occasionally there are some mutations in it. The chemical bases pair together and each pair attaches to a sugar molecule and a phosphate molecule. One pair with a sugar molecule and a phosphate molecule is called a nucleotide, and these nucleotides join together in that double helix pattern that DNA are famous for.

These pairs of letters control what kind of proteins the cell will build. Proteins are strings or amino acids and connecting the strings in different ways, or using different kinds of acids, will produce different proteins. Different proteins will do different jobs in the body. This happens in the cell. When a protein needs to be made, a molecule attaches to the DNA and reads it by moving along it. This molecule creates a copy of the DNA sequence which is called a messenger RNA. This messenger RNA tells the amino acids floating in the cell where to join up and in what order, creating different proteins. This is called encoding. That means that all of the DNA in our cells has a purpose because it tells the cells what proteins to make and without those proteins, we can’t do anything.

Well, not all of the DNA encode protein. We have an awful lot of DNA in our cells that don’t seem to do anything. They don’t seem to have a purpose, and these are the junk DNA. The trouble is, 98% of the DNA we have falls into this category. It doesn’t seem plausible that 98% of our DNA doesn’t have a purpose. The problem seems to boil down to what exactly “purpose” means. The idea “junk DNA” was introduced in the 1940s. Scientists at the time thought that only a small fraction of our DNA could be functional because if we needed 100% of our DNA, mutations would wipe us out as a species. We obviously haven’t been wiped out, so they concluded that there must be a lot of DNA that we didn’t need to function. This became the junk DNA. This junk DNA has come from many different places. It could have been encoding DNA that mutated so far that it couldn’t be used any more. It could be DNA that is just broken and can’t be used. It could be DNA that was infected by a virus and rendered inoperable. There are many places it could have come from. And this goes to show how incredible evolution is.

However, it turns out that all of this junk DNA isn’t junk and actually has a purpose, just not the same purpose as our functioning DNA. What they do appears to be a mystery, but they do have a purpose. Scientists experimented by removing part of the junk DNA from mice. When they did, half of the mice died before they were born. The junk DNA they removed seems to be important in regulating the proliferation of cells in the embryo. We have the same junk DNA. The junk DNA are also able to increase or decrease the ability of a cells DNA to create proteins.

Junk DNA could also be connected to diseases. Sometimes turning up or down a cell’s ability to create protein can be a good thing, but sometimes it can be a bad thing. There is a theory that some of the junk DNA could be connected to autism, schizophrenia, cancer, and other diseases. So much of our DNA is in this junk category that it is very difficult to work out which part of it does what. So far, it seems that some of it is vital, some of it is harmful, and some of it really is just junk. And that is what I learned today.

Sources

https://med.stanford.edu/news/all-news/2023/09/junk-dna-diseases.html

https://news.berkeley.edu/2021/10/18/so-called-junk-dna-plays-critical-role-in-mammalian-development

https://en.wikipedia.org/wiki/Junk_DNA

https://news.cuanschutz.edu/dbmi/what-is-junk-dna

https://medlineplus.gov/genetics/understanding/basics/dna

https://www.genome.gov/genetics-glossary/Deoxyribonucleic-Acid-DNA

https://www.britannica.com/science/nucleic-acid

https://en.wikipedia.org/wiki/Genetic_code