Alien Genetic Code
Our Own Genetic Code

Our genetic code has the following properties:

  • It is a fixed-length, triplet code. All the codons are 3 nucleotides in length.
     
  • It is degenerate. An amino acid may be encoded by more than one codon.
     
  • It is sequential and nonoverlapping. Three nucleotides are interpreted as a codon, then the next three are interpreted as the next codon.
     
  • There are special codons that do not determine amino acids but rather mark the end of translation.
Our Genetic Code
For example, an RNA sequence ...AGCCGUUCACUAGUCUCAUC... may be interpreted according to our genetic code: 
     AGCCG UUC ACU AGU CUC AUC...
           Phe Thr Ser Leu Ile...
            F   T   S   L   I
or
     AGCCGU UCA CUA GUC UCA UC...
            Ser Leu Val Ser Ser...   
             S   L   V   S   S
or
     AGCCGUU CAC UAG UCUCAUC...
             His stop
              H
Note that translation in your in-vitro system (unlike natural translation) can initiate anywhere in the RNA (see IN-VITRO-TRANSLATE).

Some properties are derivative. For example, the fact that our genetic code is a fixed-length triplet code and uses four nucleotides implies that there are 64 codons, no more, no less (why?). However, there is no obvious reason why there are 20 amino acids. One can imagine a genetic code with more amino acids or fewer.