Читать книгу Snyder and Champness Molecular Genetics of Bacteria - Tina M. Henkin - Страница 169

Also like RNA, polypeptides can have a secondary structure, in which parts of the chain are held together by hydrogen bonds. However, because many more types of interactions are possible between amino acids than between nucleotides, the secondary structure of a polypeptide is more difficult to predict. The two basic forms of secondary structures in polypeptides are α-helices, where a short region of the polypeptide chain forms a helix due to the interaction of each amino acid with the one before and the one after it, and β-sheets, in which stretches of amino acids interact with other stretches to form sheetlike structures (Figure 2.20). These types of structured regions are often joined together by more flexible regions known as linkers. Computer software is available to help predict which secondary structures of a polypeptide are possible on the basis of its primary structure. However, these programs are not entirely reliable, and techniques like X-ray crystallography and nuclear magnetic resonance spectroscopy provide much more detailed information about the secondary structure of a polypeptide.

Figure 2.20 Primary, secondary, tertiary, and quaternary structures of proteins.