What is the difference between sulfuric acid and alkaline?

What is the difference between a polypeptide and an amino acid residue? Thanks...?

• Can someone explain to me what an amino acid residue is? Also what is the difference between an amino acid residue and a free amino acid? I don't understand the terms " free amino acid" and "amino acid residue". Thanks so much...

• Answer:

  When two or more amino acids combine to form a peptide, the elements of water are removed, and what remains of each amino acid is called an amino-acid residue. a-Amino-acid residues are therefore structures that lack a hydrogen atom of the amino group (–NH–CHR–COOH), or the hydroxyl moiety of the carboxyl group (NH2–CHR–CO–), or both (–NH– CHR–CO–); all units of a peptide chain are therefore amino-acid residues.