Final answer:
Replacing an amino acid in a protein can alter its tertiary structure and affect the protein's backbone.
Step-by-step explanation:
The modification of the protein by replacing aspartic acid with lysine can have a significant impact on the protein's tertiary structure and affect the protein's backbone.
The tertiary structure of a protein refers to its three-dimensional folding pattern, which is crucial for its function. A change in the amino acid sequence can disrupt the interactions between side chains and alter the overall folding of the protein.
In addition, aspartic acid and lysine have different chemical properties, which can further contribute to changes in the protein's structure and function. Therefore, the correct answer is (d) Both (b) and (c).