More about the Genetic Code - start codons, stop codons and degeneracy

Still staying on the same topic of the Genetic Code...Now let's learn more about it!

When decoding information on DNA, a messenger RNA (mRNA) transcript is first made by the process of transcription. The first codon on this mRNA transcript is almost always "AUG" which codes for the amino acid "methionine" or "M". This is referred to as the START codon. If you noticed, I had intentionally started my New Year's wish for you with "M" too!

aug
M A N Y

H A P P Y

D A Y S !

As the saying goes - where there is a beginning, there is also an end. In the case of a mRNA transcript, where there is a start codon, there is also a stop codon. In the Genetic Code, there are 3 different STOP codons that can be used. Any 1 of these 3 stop codons may be found at the end of a mRNA transcript.

The start codon "M" is indicated in orange and 3 stop codons are indicated in red, in the Genetic Code table below.

The 3rd noteworthy point about the Genetic Code is - DEGENERACY.

If you had been decoding my New Year's wish for you in my earlier post (5th Jan '08), you may have realized that the 3 "A"s found in the coded message were coded for by 3 different codons. Similarly so, for the 3 "Y"s and 2 "P"s.

gcc uau
M A N Y

gcg ccc cca uac
H A P P Y

gca uau
D A Y S !

This feature of the Genetic Code, where there is more than 1 codon coding for the same amino acid is termed "DEGENERACY".

I hope with this, you now understand start codons, stop codons and degeneracy of the Genetic Code! You can then create your own "DNA" encoded message! How about sending me one to decode! ;p