The building blocks of protein are which of the following?

• A. Amino acids
• B. Nucleotides
• C. Sugars
• D. Lipids

Answer: (A)

Proteins are built from amino acids, the building blocks that link together in long chains called polypeptides. Each amino acid has an amino group and a carboxyl group that form peptide bonds with neighbors, creating a backbone with distinctive side chains that determine how the chain folds and functions. About 20 standard amino acids provide the diversity needed for proteins to have a vast range of shapes and activities, from catalyzing reactions to providing structure and signaling. The other listed molecules serve different roles: nucleotides form nucleic acids like DNA and RNA, sugars make up carbohydrates, and lipids form fats and membranes. They are not the repeating units that construct proteins, so amino acids are the correct building blocks of proteins.