Proteins Amino Acids

The peptide bond trap you need to fix: NEET regularly asks how many peptide bonds form when a given number of amino acids polymerise. Students who answer "N" instead of "N − 1" lose marks on what should be a free recall question.

α-Amino acids are organic compounds carrying both an amino group (−NH₂) and a carboxyl group (−COOH) bonded to the same carbon — the α-carbon. NCERT Class 12 Chemistry Chapter 6 (Part 2), page 10, defines them as the building blocks of proteins. Except glycine (R = H), all α-amino acids have a chiral α-carbon, making them optically active. Naturally occurring amino acids in proteins are L-configuration.

Peptide bond formation is a condensation reaction: the −COOH of one amino acid reacts with the −NH₂ of the next, releasing one water molecule and forming an amide (−CO−NH−) linkage. This bond is:

• Planar and rigid (partial double-bond character from resonance)
• Trans configuration in most proteins
• Covalent — not broken by denaturation

For a linear chain of N amino acid residues, exactly N − 1 peptide bonds form and N − 1 water molecules are released (NCERT Class 12 Chemistry Chapter 6, Part 2, page 12).

NEET watch-out: The question may phrase it as "dipeptide" (1 bond), "tripeptide" (2 bonds), or give a residue count and ask for bonds or water molecules lost. The answer is always residue count minus one.

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