Characteristics of genetic code

Characteristics of genetic code

Following are the characteristics of genetic code accepted world wide

1. Only 61 triplets or codons code for amino acids
   3 stop codons (aka nonsense codons or terminator codons) UUA UAG UGA.
    
2. The code is a degenerative code
   Several codons code for the same amino acid.
   The first two letters seem to be the most important the third one tends to be interchangeable
3. The is no punctuation between each codon.
   The reading frame is set at the beginning of the gene. Frame shift mutations can be caused by the ADDITION or DELETION of only one or two bases. Everything downstream is misread.
    
4. The reading of mRNA is always in the same direction 5’ to 3’ (the same way as transcription and replication).
   The polypeptide chain is constructed from the amino end to the carboxyl end.
    
5. The code is universal for all organisms. So it is very ancient.
    
6. Similar amino acids have similar codons.
   Example
   Aspartic acid codons GAU and GAC. Glutamic acid codons GAA and GAG. Both are acidic amino acids.
    
7. Some amino acids are chemically altered AFTER translation.
   e.g. In collogen proline is converted to hydroxyproline.