DNA is a long strand of bases. A triplet code is a sequence of three bases along this strand.
Why three? Diversity. There are four different bases. These bases need to code for all 20 amino acids.
Each triplet of bases stands for one type of amino acid. If each code were only two bases long (a doublet) the codes available would be too limited to provide codes for 20 unique amino acids.
By having triplet codes in the four bases, we are able to provide codes for 64 different triplets. We only need 20 so some of these triplets are able to be dedicated start and stop codons.
Codon: three letter unit of an mRNA molecule.
All 64 codons have been discovered and 3 of them have been determined to be stop codons.
During transcription, an amino acid is added wherever there is a triplet code.
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