Codons are present on:

Ans. A. mRNAa. The codons are composed of the four nucleotide bases, namely, the purines (adenine and guanine) and the pyrimidines (cytosine and uracil).b. The three-nucleotide base sequences in mRNA that act as code words for amino acids in protein constitute the genetic code or simply codons.c. The three codons UAA, UAG and UGA do not code for amino acids and they act as stop signals in protein synthesis. These three codons are known as termination codons or non-sense codons.d. The codons UAA, UAG, UGA are known as Ochre, Amble and Opal codons.e. The codons AUG and sometimes GUG are the chain initiating codons. AUG serves as initiating codon, beside coding for methionine residue in protein synthesis.