If you were given the AMINO ACID sequence, you could come up with a working DNA sequence, but even though this sequence may still make the same protein, it may not be the same DNA sequence that the original protein was coded from. This is due to the fact that there 64 different combinations for the four bases in DNA (A, T, C, & G), but only 20 amino acids to code for, therefore there's going to be overlap and there will be different codons that code for each amino acid