Final answer:
To change the Na/Glucose symporter to transport fructose, the glucose binding site must be mutated. This affects the molecule's specificity for transport without altering fundamental transport mechanisms or ionic gradients.
Step-by-step explanation:
To alter the Na/Glucose symporter to transport fructose instead of glucose, one would need to mutate the glucose binding site. This is because the glucose binding site is responsible for the specificity of the molecule that the symporter will transport. Mutating the Na+-binding site, ATP-binding site, or the transmembrane domain would not change the specificity of the transporter towards glucose or fructose. It is important to remember that such a mutation could affect the transporter's ability to recognize or bind fructose or could even render the symporter nonfunctional, depending on the nature and extent of the mutation.