Proteins comprise long chains of amino acids joined together by peptide bonds.
A peptide bond is formed by the carboxyl group of one amino acid linking to the amino group of the next one.
Arbitrarily proteins are categorized according to length of the amino acid chain: peptides (2-10 amino acids), polypeptides (11-99 amino acids) and chains of approximately 100 amino acids or more are proteins .
Glycoproteins are proteins with a carbohydrate component and lipoproteins are proteins with a lipid component.
The sequence of amino acids in the protein chain is called the primary structure. The basic chains are then folded and torsed in complex ways to form the secondary structure. As these folded twisted chains are further organized into larger crystals (etc.) the arrangement is called the tertiary structure. Finally some protein macromolecules are comprised of several protein subunits and the overall arrangement is known as the quaternary structure, e.g. hemoglobin.
Peptide receptor radionuclide therapy (PRRT)
Some peptides, capable of binding specific transmembrane receptors, labeled with ß- emitting radionuclides, such as Y-90 (Y-DOTATOC, Y-DOTALAN) and Lu-177 (Lu-DOTATATE) are used for the medical nuclear therapy of numerous tumors .