Final answer:
The first triplet in every protein coding region codes for the amino acid methionine.
Step-by-step explanation:
The first triplet in every protein coding region codes for the amino acid methionine. It is specified by the codon AUG, which also serves as the start codon to initiate translation. The reading frame for translation is set by the AUG start codon near the 5' end of the mRNA.