Organic Chemistry MCAT Practice Exam

What structural feature makes peptide bonds unique compared to other bonds?

1. They are flexible and can rotate

2. They have partial double bond character

3. They can easily hydrolyze spontaneously

4. They form only in acidic environments

The correct answer is: They have partial double bond character

Peptide bonds are unique due to their partial double bond character, which arises from resonance between the carbonyl group (C=O) and the nitrogen atom (N-H) of the peptide linkage. This resonance means that the peptide bond has characteristics of a double bond, giving it rigidity and preventing free rotation around the bond. The resulting planarity (flat structure) of the peptide bond contributes significantly to the overall structure and stability of proteins. The partial double bond character restricts the rotational freedom that typically accompanies single bonds, which is a key distinction when comparing peptide bonds to other types of bonds. This characteristic plays a crucial role in protein folding and stability, as it helps to maintain defined geometrical arrangements in protein structures. Understanding the unique nature of the peptide bond is essential for insights into protein chemistry, as it directly influences the conformation and function of proteins. The other options, although relevant in their own contexts, do not accurately represent the distinct structural feature that defines peptide bonds.