Answer: The option that is not true is D) Each amino acid is specified by only one codon.
Codon can be defined as the sequence of three nucleotides ( present in DNA or mRNA) that corresponds to a particular amino acid. It helps in the process of translation as different amino acids ( that are linked to codons) are assembled to give a particular protein according to the sequence of codon.
There are 64 codons and 20 amino acids that make up the proteins present in the living systems. This indicates that several different codons can correspond to the same amino acid.
For instance, amino acid Valine is coded by four codons that is GUC, GUG, GUA, GUU.
Thus, option D) is incorrect.
