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My attempt: First I took the single letter AA codes and made them amino acids. So, the first one is Trp which is 5'-UGG-3'. From this I got the DNA sequence 3'-CCA-5'. However, the correct answer (shown in red) doesn't have this sequence. What did i do wrong?

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up vote 7 down vote accepted

Your approach to translate the AA sequence, codon by codon, was correct. This was a bit of a trick question because to recognize it, you had to read the sequence backwards.

UGG-CAA-GGT-CAC etc is read directly off of the 3'->5' strand of the circled answer, reading from right to left.

The bottom left is a red herring because it starts with a start codon, ATG, but reading beyond the start codon, the sequence wouldn't match.

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