Polypeptides, amino acid sequence hydrogen bridges

In proteins, the 20 different a-L-amino acids (Box 19.1) are linked in specific sequence by peptide bonds to form linear polypeptides of molecular weight in the range of a few thousand to several hundred thousand. If a protein contains cysteines, these can cross-link by oxidation to form disulfide bridges. Besides these covalent bonds, the main stabilization of the very complex three-dimensional (tertiary) structure, which is characteristic for each protein, is by hydrophobic and van der Waals forces and, even more importantly, by hydrogen bonds [133, 134, 586-589]. 

Tertiary structure the way in which the polypeptide chains of a protein fold into a characteristic three-dimensional shape, stabilized by bonds between amino acids far apart in the sequence. These bonds may be strong covalent interactions such as disulfide bridges or weaker interactions involving hydrogen bonds or salt bridges. 

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