To start off on this massive topic I would like to note a couple of key concepts:
- Proteins are made of smaller molecules called amino acids.
- Humans use 20 amino acids to make all of our proteins.
- DNA has to somehow code for each of these amino acids.
- DNA on the other hand is made up of nucleotides.
- There are 4 different types of nucleotide.
Some pictures which may help:
To make it easier we will call the nucleotides A, G, T and C.
These nucleotides make up the different parts of the ‘code of life‘. What they code for are the twenty amino acids.
This is how:
Every combination of 3 nucleotides, codes for one amino acid. This is called a ‘codon’.
That sounds simple enough right?
However, there are 64 different possible combinations. That is 64 different codons for only 20 amino acids. So as a result some amino acids have more than one codon. For example Leucine can be coded for with:
- and GAC
Note how they are all very similar? This is to prevent a mutation from having any significant effect. (for example, if we had the codon GAC, and there was a mutation on the last nucleotide, C, it could turn into any other nucleotide, A, T or G, and it wouldn’t matter. Leucine would still be produced.) This is just one of the many mechanisms the body uses to prevent mutation.
Some codons are used to define when to ‘stop’ and when to ‘start’.
So now we know:
- A codon is a set of three nucleotides on DNA.
- Each codon stands for one of the 20 amino acids.
- The amino acids are what make up protein.
Next is to explain how we turn this code into protein. That’s a bit more complicated.