Making proteins

What are proteins made of?

The ingredients of a protein are amino acids. To build a protein we need to build a long chain of amino acids. There are 20 different types of amino acids, so there are lots of different protein chains we can build. Biologists give amino acids a code letter, as for DNA. This is much easier than writing out the whole name each time. For example, M is methionine, L is leucine, F is phenylalanine (because P is proline).

Three DNA letters, one amino acid?

The DNA code uses groups of three 'letters' to make meaning. This means that when the cell reads the instructions encoded in the DNA sequence to make a protein, it reads it three letters at a time. Most groups of three letters - known as triplets or codons - code for an amino acid.

Since there are four different DNA letters (A, G, C and T), there are 4 x 4 x 4 = 64 different combinations that can be used. However, as there are only 20 different types of amino acid, some of these 64 codons code for the same amino acid. Some of the 64 codons don't code for any of the amino acids. Instead they provide the punctuation and grammar, like where the cell should start and stop reading the sequence.