Question:
Cystic fibrosis is a genetic condition that is associated with defects in the CFTR protein. The CFTR protein is a gated ion channel that requires ATP binding in order to allow chloride ions (Cl−) to diffuse across the membrane.
(a) In the provided model of a cell, draw arrows to describe the pathway for production of a normal CFTR protein from gene expression to final cellular location.
(b) Identify the most likely cellular location of the ribosomes that synthesize CFTR protein.
(c) Identify the most likely cellular location of a mutant CFTR protein that has an amino acid substitution in the ATP-binding site.
▶️Answer/Explanation
(a)
(b) Answer: Endoplasmic Reticulum (specifically, the rough ER)
CFTR is a membrane protein, so it’s synthesised by ribosomes bound to the rough ER, not free-floating in the cytoplasm.
(c) Answer: Endoplasmic Reticulum
- A CFTR protein with a faulty ATP-binding site is misfolded.
- Misfolded proteins are usually detected and retained in the ER, then targeted for degradation.
- So, it won’t reach the Golgi or plasma membrane, and gets stuck in the ER.