Peptide Bonds and Protein Primary Structure (1A) Practice Test

A protein engineering team compares two purified proteins that share identical amino acid composition but differ in sequence order. Both proteins lack cysteines and show similar overall size by mass spectrometry. One protein resists backbone cleavage under mild acid conditions more than the other. Assuming no post-translational modifications, which statement best links peptide bonds and primary structure to the observed difference in stability?

Researchers design a short peptide hormone analog for sustained circulation time. Compared with the native hormone, the analog contains one additional residue inserted between positions 5 and 6, confirmed by intact-mass shift and sequencing. Receptor binding decreases despite similar net charge and no cysteine residues in either peptide. Which statement best explains the primary-structure consequence of inserting a residue with respect to peptide bond connectivity?