Читать книгу Materials for Biomedical Engineering - Mohamed N. Rahaman - Страница 72

The tertiary structure of a protein refers to the overall three‐dimensional shape (conformation) of its polypeptide chain. Many proteins do not have the regular structure of the α‐helix or β‐sheet but, instead, rely for their properties on their tertiary structure. A polypeptide chain can fold in a complex manner to give a variety of three‐dimensional shapes, but two broad classes of structures, referred to as globular and fibrous, are often distinguished. In globular proteins, the polypeptide chain is more compactly folded like a ball of string with an irregular surface. In comparison, the polypeptide chain in fibrous proteins have a more elongated or filamentous three‐dimensional structure (Figure 2.22). A fibrous protein often has a length that spans a longer distance than the average diameter of a globular protein.

Figure 2.22 Schematic illustration in two dimensions of the overall three‐dimensional shape of (a) globular proteins and (b) fibrous proteins.