Assuming you do not know the location of the start codon how

Assuming you do not know the location of the start codon, how many possible reading frames are there in a mRNA?

Solution

Open reading frame (ORF): It is defined as the reading frame of a gene which possesses the ability to code for protein. It is an open frame which must start with AUG or ATG which further resembles that the chain initiation of peptide started and ends with stop codons which can be UAA, UAG or UGA.

As the starting codon contains three bases, each DNA strand contains three reading frames that start at the 1^st, 2^nd and 3^rd bases. As the DNA is double stranded, each DNA contains six reading frames. As the mRNA is single stranded, three open reading frames are possible (because three base code indicates one amino acid)