The code has several important properties. The first we’ve already seen—it is a triplet code.  The second you may have just stumbled on yourself, when you noted that phenylalanine appears more than once in the table. This is because the genetic code is a degenerate code. That doesn’t mean it sits around all day smoking cheap cigarettes and looking at internet porn. It means that a particular amino acid can be coded for by more than one codon. Think about it—with 4 letters arranged into triplets, there are 4³ = 64 possible codons. But there are only twenty amino acids. This leaves plenty of room to come up with alternate codons for some amino acids, and also to introduce special codons. For example, the codon AUG not only codes for methionine, but is also the start codon, which begins every mRNA transcript and tells the ribosome where to begin translation. UAA, UGA and UAG are stop codons, which tell the ribosome to terminate translation and release the completed protein.