Improving science literacy – part 6

A Primer on Mutations

You shouldn’t necessarily be afraid of mutations; they can, in fact, be your friend. Like pretty much everything else in this world it depends on the context.

The first thing you should understand from the last post is that DNA doesn’t do a whole lot by itself. Instead, the DNA strands act through RNA to create proteins. It is these proteins that do all of the important work in your body which biologically matter. Through the hard work of many scientists we’ve known the secret code (see below) for a while now and it turns out to be fairly simple: a group of three nucleotides in a row (AAA, AAC, AAG, and so forth) code for a single amino acid (along with a few that code for when the the protein should start and stop).

codon(source)

Each of these groups of three nucleotides (also known as triplets) is called a “codon.” Get it? Code. Codon. See, science occasionally makes sense. So, lets use some actual codons in a quick example: (please note, this isn’t exactly correct, but it’s being used only as a simplified example so it’s okay)

———DNA ———————-> RNA —————-> Protein

AAG GTT CTC ATG ————————————-Phe-Gln-Glu-Tyr

——————————- UUC CAA GAG UAC

So, these twelve nucleotides of DNA code for complementary nucleotides of RNA. Groups of three nucleotides of the RNA strand code for singular amino acids and we’re left with a protein made of four linked amino acids.

Now that you know generally how this process works you can being to understand what mutations actually are and how they function. Mutations actually come in quite a few flavors: point, deletions, insertions, inversions, duplications, etc. However, all follow the same general principles, so if you understand one you will most likely understand the others by their name alone (which describe exactly what is happening to the DNA). So, I’ll explain two types and let you figure out the rest. If you can’t just ask me to explain it in the comments.

Point Mutations: Changing a single nucleotide in the original DNA can have either a dramatic effect or none at all depending on what has changed.

———DNA ———————-> RNA —————-> Protein

AAG GTT CTG ATG ————————————-Phe-Gln-Asp-Tyr

——————————- UUC CAA GAC UAC

See how changing that one little nucleotide in the DNA completely changed the protein?  That could have one of three biological effects: it could completely destroy the function of the protein, it could have no (significant) effect on it’s function, or it could actually improve the function of the protein (yes, it actually does happen, but that’s a whole other story…).

———DNA ———————-> RNA —————-> Protein

AAA GTT CTC ATG ————————————-Phe-Gln-Glu-Tyr

——————————- UUU CAA GAG UAC

This is called a silent mutation because while the DNA suffered a mutation it had no effect on the final makeup of the protein and is therefor neutral in regards to evolution.

Deletion: This is exactly what it sounds like.  Most times only one nucleotide is removed so that’s what we’ll focus on.

———DNA ———————-> RNA —————-> Protein

AAG GTTTC ATG ————————————-PheGlnSer

——————————- UUC CAAAG UAC

This is called a reading frame shift.  Just getting rid of a nucleotide doesn’t change the fact that codons are needed for the final protein to be translated from the RNA.  Instead, it shifts the code one nucleotide over (and since three are needed for an amino acid, in our example there is RNA overhang that essenatially does nothing).

I hope this makes a little bit of sense and begins to open your eyes to the wonderful world of genetics.  Of course, the way this actually goes down is much more complicated and nuanced, but I feel my explanation is a good introduction to any interested lay person (as I hope all of you are).  As before, any and all questions are welcome.

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