Amino Acid General Structure Defines Minimum Carbons

Steps:

• Recall the general formula of an amino acid: H₂N-CH(R)-COOH, where R is the side chain.
• Identify glycine as the simplest amino acid, with R = H.
• Count the carbons: one alpha carbon (CH) and one carboxyl carbon (COOH).
• Confirm no standard amino acid has fewer than two carbons.

Why B is correct:

• Glycine (C₂H₅NO₂) has exactly two carbon atoms, matching the minimal alpha and carboxyl carbons required by the amino acid definition.

Why the others are wrong:

• A: One carbon cannot form the required alpha carbon plus carboxyl group structure.
• C: Three carbons exceed the minimum seen in glycine.
• D: Four carbons exceed the minimum seen in glycine.

Final answer: B