Question:

Which of the following is correct regarding genetic code?

UUU is the initiation codon which also codes for phenylalanie.

There are64triplet codons and only20amino acids.

Three random nitrogen bases specify the placement of one amino acid.

UAA is the nonsense codon which also codes for methionine.

Solution:

There are 64 triplet codons which code for 20 amino acids. This is due to the degeneracy of the code as some amino acids are influenced by more than one codon. Only tryptophan and methionine are specified by single codons. All other amino acids are specified by two (e.g., phenylalanine-UUU, UUC) to six (e.g., arginine- CGU, CGC, CGA, CGG, AGA, AGG) codons.