A peptide bond is

• A. Amino group and carboxyl group bonded to the alpha-carbon
• B. A double carbon bond
• C. A tertiary ring of amino group and carboxyl group bonded to the alpha-carbon
• D. Two amino groups bonded to the alpha-carbon

Answer: (A)

A peptide bond is the covalent linkage between amino acids formed by condensation between the carboxyl group of one amino acid and the amino group of the next, resulting in an amide bond with resonance (-CO-NH-). This connection is what links amino acids into proteins.

Among the given statements, the one that mentions the amino group and the carboxyl group associated with the alpha-carbon points to the key groups involved in forming this linkage. While the actual bond forms between two different amino acids (carboxyl of one and amino of the next), this option at least references the two functional groups central to peptide bonding, making it the best match among the choices. The other statements mischaracterize the bond as a double bond, a ring, or two amino groups bonded to the same alpha-carbon.