Final answer:
Most CFTR folding occurs in the endoplasmic reticulum, where proteins fold into their functional structures. In cystic fibrosis, a mutated CFTR gene leads to defective folding, resulting in protein degradation and impaired Cl- transport, causing the accumulation of thick mucus.
Step-by-step explanation:
Most CFTR folding is done in the endoplasmic reticulum of the cell, where newly synthesized proteins fold into their functional three-dimensional structures. The folding process is critical because it determines whether the CFTR protein will be trafficked to the cell membrane or degraded. Proper folding is essential for CFTR to function as a chloride channel in the cell membrane and to facilitate active transport of Cl- ions.
When the CFTR gene is mutated, as in cystic fibrosis (CF), it results in a defective channel protein. This malfunctioning CFTR channel is not incorporated into the cell membrane and is instead degraded. Consequently, Cl- transport is reduced, leading to thick and sticky mucus, particularly in the lungs, and increased susceptibility to bacterial infections.