<P> In molecular biology, a reading frame is a way of dividing the sequence of nucleotides in a nucleic acid (DNA or RNA) molecule into a set of consecutive, non-overlapping triplets . Where these triplets equate to amino acids or stop signals during translation, they are called codons . </P> <P> A single strand of a nucleic acid molecule has a phosphoryl end, called the 5 ′ - end, and a hydroxyl or 3 ′ - end . These define the 5' → 3' direction . There are three reading frames that can be read in this 5' → 3' direction, each beginning from a different nucleotide in a triplet . In a double stranded nucleic acid, an additional three reading frames may be read from the other, complementary strand in the 5' → 3' direction along this strand . As the two strands of a double - stranded nucleic acid molecule are antiparallel, the 5' → 3' direction on the second strand corresponds to the 3' → 5' direction along the first strand . </P>

Assuming that the reading frame starts with the first triplet what is the codon for a