Cystic fibrosis is associated with a defect in which aspect in bronchial epithelium?

• A. Protein structure
• B. Carbohydrate metabolism
• C. Lipid synthesis
• D. Nucleic acid polymerization

Answer: (A)

Cystic fibrosis affects a membrane protein, the CFTR chloride channel, on bronchial epithelium. The disease stems from a mutation that disrupts the protein’s proper folding, processing, and function at the cell surface. When this channel doesn’t form or work correctly, chloride and water movement across the airway surface is impaired, making mucus thick and sticky and promoting infection. So the key idea is a defect in the structure and handling of a protein—the CFTR channel—not in metabolic processes like carbohydrate metabolism, lipid synthesis, or nucleic acid polymerization.