Elementary plant Biochemistry and Biotechnology (2+1)

Genetic Code

 
• The genetic code is the collection of base sequences (called as codons) that corresponds to each amino acid and to stop signals for translation.
• Since there are 20 amino acids, there must be more than 20 codons to include signals for starting and stopping the synthesis of particular protein molecules.
• If one assumes that all codons have the same number of bases, then each codon must contain at least three bases. Because: A single base cannot be a codon since there are 20 amino acids and only 4 bases.
  
• Pairs of bases also cannot serve as codons because there are only 42 = 16 possible pairs of four bases.
  
• Triplets of bases are possible because there are 43 = 64 triplets, which is more than adequate.
• In many cases, several codons designate the same amino acid- that is the code is redundant or degenerate.
• In the in vitro system, protein synthesis can start at any base.
• However, in vivo it starts only at AUG codon. Similarly it stops at either UAA, UGA or UAG.

The universal genetic code