Question

Cystic fibrosis (CF) is an inherited disorder caused by different types of mutations, many of which prevent ions from moving across cell membranes. Normally there are channel proteins that allow passage of the ions, but in patients with one kind of CF these proteins seem odd. Closer examination shows that these proteins display the correct amino acid sequence. However, they fail to do their job. A) Given that the primary structure of the protein is correct, what can you infer about the DNA sequence of this patient, is there a mutation? Explain. B) Why is the primary structure insufficient to guarantee the proper function of the protein?

Answer 1

Ans a) In CF, the CFTR protein which helps in moving chloride or ions across the cell membrane becomes dysfunctional. This leads to the mucus in the organs to become thick and sticky. When the primary structure of the protein is correct, it can be inferred that the DNA has no mutation and the mutation has taken place in the assisting proteins which does not allow the movement of the ions. The most common reason for CF is deletion of a codon or a three DNA base from the CFTR gene but in this case the primary structure is fine. This means that there is no mutation but there might be problem with the folding of the protein and hence it might not be able to facilitate the movement of the ions.

Ans b) The primary structure is not sufficient to guarantee proper function of the protein because despite the right amino acid sequence and no mutation, there might be problem with the protein and hence it might not help transport ions across the membrane. There are accessory proteins which also play a critical role in the transport and when they are absent or there is a mutation in them, it might cause cystic fibrosis.