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  1. Amino acid | Definition, Structure, & Facts | Britannica

    Dec 17, 2025 · Amino acid, any of a group of organic molecules that consist of a basic amino group, an acidic carboxyl group, and a unique organic side chain. The term amino acid is short …

  2. Amino acid - Building Blocks, Structure, Functions | Britannica

    Nov 22, 2025 · After they are incorporated into a peptide, the individual amino acids are referred to as amino acid residues. Small polymers of amino acids (fewer than 50) are called …

  3. Structure and properties of amino acids | Britannica

    amino acid, Any of a class of organic compounds in which a carbon atom has bonds to an amino group (―NH2), a carboxyl group (―COOH), a hydrogen atom (―H), and an organic side …

  4. Protein - Amino Acids, Structure, Function | Britannica

    Nov 29, 2025 · Although more than 100 amino acids occur in nature, particularly in plants, only 20 types are commonly found in most proteins. In protein molecules the α-amino acids are linked …

  5. Amino acid - Reactions, Structure, Synthesis | Britannica

    Dec 17, 2025 · Amino acid - Reactions, Structure, Synthesis: Amino acids via their various chemical functionalities (carboxyls, amino, and R groups) can undergo numerous chemical …

  6. Acid | Definition, Examples, Types, Uses, & Facts | Britannica

    Dec 12, 2025 · What are the 20 amino acid building blocks of proteins? What is the difference between standard and nonstandard amino acids?

  7. What is an amino acid? | Britannica

    An amino acid is an organic molecule that is made up of a basic amino group (−NH 2), an acidic carboxyl group (−COOH), and an organic R group (or side chain) that is unique to each amino …

  8. amino acid - Students | Britannica Kids | Homework Help

    Chemists define an amino acid as any group of organic molecules that consist of a basic amino group (–NH 2), an acidic carboxyl group (–COOH), and a specific organic side chain that is …

  9. Amino acid - Origin, Life, Earth | Britannica

    Nov 22, 2025 · Amino acid - Origin, Life, Earth: The question of why organisms on Earth consist of l-amino acids instead of d-amino acids is still an unresolved riddle.

  10. Phenylalanine | Amino Acid, Protein, Metabolism | Britannica

    Nov 4, 2025 · An amino acid is an organic molecule that is made up of a basic amino group (−NH 2), an acidic carboxyl group (−COOH), and an organic R group (or side chain) that is unique to …