A very large structural protein contains 1,250 amino acids. Assuming one peptide bond links each adjacent pair of amino acids and that each amino acid contributes one backbone nitrogen, calculate (a) the number of peptide bonds in this protein and (b) the number of backbone nitrogen atoms. Show your work.

• A. 1,250 peptide bonds and 1,249 backbone nitrogen atoms because peptide bond formation removes one nitrogen atom from the chain.
• B. 1,249 peptide bonds and 624 backbone nitrogen atoms if only half of residues contained nitrogen in their backbone.
• C. 2,500 peptide bonds and 2,500 backbone nitrogen atoms assuming a duplicated backbone structure with two peptide bonds per amino acid.
• D. 1,249 peptide bonds and 1,250 backbone nitrogen atoms.

Answer: (D)