A particular error in the CFTR gene results in the replacement of the amino acid Phe with Ser at residue 508 of the CFTR protein. Individuals afflicted with CF most often experience the presence of thick, dry and sticky mucus in the lungs, leading to chronic infections and breathing problems. Explain why such an amino acid replacement would result in the production of the thicker mucus in the lungs.

Cystic fibrosis (CF) is a genetic disorder caused by mutations in the CFTR (cystic fibrosis transmembrane-conductance regulator) gene, which encodes the CFTR protein. The cells of the lining of the lungs contain high levels of the CFTR protein in their membranes. Normally, CFTR contains a chloride ion channel, which permits chloride ions to pass from inside the cells to the cells’ surfaces. The surface chloride ions are able to attract water in the lungs, allowing for the formation of a water layer on the cells’ surfaces. This thin water layer is necessary to allow the cilia, the tiny hairs on the surface of the lining cells to move back and forth easily. This motion permits the removal of mucus from the lungs. A particular error in the CFTR gene results in the replacement of the amino acid Phe with Ser at residue 508 of the CFTR protein. Individuals afflicted with CF most often experience the presence of thick, dry and sticky mucus in the lungs, leading to chronic infections and breathing problems. Explain why such an amino acid replacement would result in the production of the thicker mucus in the lungs.