On the mRNA molecule, AAA codes for UUU; UUU delivers a phenylalanine amino acid to a growing polypeptide (Daempfle, 2016). AAA is called a triplet sequence on DNA. Its corresponding sequence on mRNA is termed a codon. A codon is a standard genetic code in which a sequence of three nucleotides codes for a specific amino acid. Start codons and stop codons signal the cell to start or stop translation. So if the DNA sequence listed in the question were changed to AAA after G, it would indicate a stop translation.
References
Daempfle, P. (2016). Essential Biology: An Applied Approach. Dubuque, IA: Kendall Hunt Publishing