Question

In a double-stranded DNA coding for a protein, in principle, how many codon reading frames are possible?

• A. 1
• B. 2
• C. 3
• D. 6

Answer 1

The correct option is C 3

A set of three nucleotides makes a codon which in turn codes for a specific amino acid. The nucleotide triplet codons are read in a successive non-overlapping fashion which means that no two codons share a nucleotide. A specific first codon in the sequence determines the reading frame, in which a new codon begins every three nucleotide residues. For example, a DNA sequence “AAAGGGTTTCCC” can have three possible reading frames:

1. AAA’GGG’TTT’CCC,

2. A’AAG’GGT’TTC’CC

3. AA’AGG’GTT’TCC’C.

Thus, any given single-stranded DNA or mRNA sequence can have three possible reading frames each of which gives a different sequence of codons. Thus, the correct option is C.