How does DNA encode the information for a protein? There are only four DNA bases, but there are 20 amino acids that can be used for proteins. So, groups of three nucleotides form a word ( codon ) that specifies which of the 20 amino acids goes into the protein (a 3-base codon yields 64 possible patterns (4*4*4), which is more than enough to specify 20 amino acids. Because there are 64 possible codons and only 20 amino acids, there is some repetition in the genetic code. Also, the order of codons in the gene specifies the order of amino acids in the protein. It may require anywhere from 100 to 1,000 codons (300 to 2,000 nucleotides) to specify a given protein. Each gene also has codons to designate the beginning ( start codon ) and end ( stop codon ) of the gene. Building a Protein: Transcription Building proteins is very much like building a house: The master blueprint is DNA, which contains all of the information to build the new protein (house). The working copy of the ma...