Why is it important to use the correct set of pKa values for amino acid residues instead of free amino acids when calculating the net charge of a peptide?

• A. Because the pKa values for residues are always lower.
• B. Because the microenvironment can shift pKa values, affecting charge calculations.
• C. Because the pKa values for residues are always higher.
• D. Because free amino acids do not have ionizable groups.

Answer: (B)