How does an amide linkage differ structurally from a carboxyl group?

• A. An amide linkage contains a sulfur atom, whereas a carboxyl group contains an oxygen atom.
• B. An amide linkage contains a methyl group, whereas a carboxyl group contains an amino group.
• C. An amide linkage contains a nitrogen atom, whereas a carboxyl group contains a hydroxyl group.
• D. An amide linkage contains a phosphate group, whereas a carboxyl group contains a carbonyl group.

Answer: (C)