Đường đứt nét cho thấy các liên kết hydro ổn định các loại cấu trúc thứ cấp. Các liên kết hydro-α xoắn intrastrand, nghĩa là, hình thành giữa các xương sống cacbonyl oxy và hydro amide axit amin lên xoắn. R nhóm đại diện cho chuỗi bên trong xoắn-α. | 12 USMLE Road Map Biochemistry Figure 2-2. Structures of a-helix and P-sheet. Dashed lines indicate hydrogen bonds that stabilize these types of secondary structure. The hydrogen bonds of the a-helix are intrastrand ie formed between the backbone carbonyl oxygen and the amide hydrogen four amino acids up the helix. R groups represent the side chains in the a-helix. Side chains that would project above and below the plane of the page in the P-sheet structures have been omitted for clarity. Hydrogen bonds stabilizing the P-sheet are interstrand ie formed between groups on neighboring strands. J 2. In some multisubunit proteins such as immunoglobulins the subunits are held together by disulfide bonds or other covalent interactions. CYSTIC FIBROSIS Failure of a critical chloride transport protein to fold properly into its functional conformation contributes to many cases of cystic fibrosis CF which is the most common fatal inherited disorder of white people. CLINICAL CORRELATION Chapter 2 Protein Structure and Function 13 The gene responsible for CF codes for the cystic fibrosis transmembrane conductance regulator CFTR which is a chloride channel expressed on the surface of epithelial cells that line the affected organs. Approximately 70 of CFTR mutants worldwide are due to deletion of a single phenylalanine SF508 that interferes with CFTR folding this mutant CFTR is recognized as abnormal and is degraded broken down . Patients with CF suffer from thick mucous secretions in the airways as well as the pancreas and intestinal lining due to impaired chloride absorption and consequent fluid imbalance. - These thick mucous secretions are difficult for the mucociliary cells of the airway to clear resulting in chronic airway obstruction inflammation and frequent lung infections. - Decreased secretion of pancreatic enzymes leads to impairment of the digestive functions of the intestine. IV. Collagen A. Collagen is an abundant protein that provides the structural framework for
