In biochemistry, a residue is a single unit within a polymer, such as an amino acid within a protein. It represents the building block after losing water during peptide bond formation.

In biology, and specifically in biochemistry, residues are the individual organic compounds called amino acids that comprise some of the building blocks of complete proteins. The amino acids involved in protein building, structure and regulation are leaked after a protein is formed; this is why they are called residues.

A residue is a single molecular unit within a polymer. Residue is thus another term for monomer. Although the term residue is most often used to refer to a specific amino acid within a polypeptide, it is also used to refer to sugars within a carbohydrate molecule and nucleotides within deoxyribonucleic acid (DNA) or ribonucleic acid (RNA).

In biochemistry and molecular biology, a residue refers to a specific monomer within the polymeric chain of a polysaccharide, protein or nucleic acid. In proteins, the carboxyl group of one amino acid links with the amino group of another amino acid to form a peptide. This results in the removal of water and what remains is called the residue.

residue The part of a single sugar that appears in a polysaccharide; of a single amino acid in a protein; of a single nucleotide in a nucleic acid, etc.; usually the monomer minus the elements of water.