Key background concept: higher order structure

The sequence of the 20 amino acids encoded by the DNA is responsible for the particular three-dimensional shape ("tertiary structure") of the protein molecule. This shape largely determines the function of the protein. For example, it is common that a specific fold in the protein must be present to allow an enzyme to bind to its substrate, and therefore interact with it. If the DNA sequence is altered so that a different amino acid is present at the critical position in the protein, then this mutant protein may no longer be able to recognize the substrate .... this is why the DNA sequence is so important!