Passage
The cystic fibrosis transmembrane conductance regulator (CFTR) protein is a chloride ion channel involved in the production of mucus, sweat, and digestive fluids. CFTR is composed of five domains (Figure 1) : Two transmembrane domains (TMD1 and TMD2) , two nucleotide binding domains (NBD1 and NBD2) , and one regulatory domain (R domain) .
Figure 1 Schematic diagram of CFTR domainsThe NBD domains regulate CFTR activity by binding ATP, which causes a conformational change in the TMD domains. This change allows chloride ions to leave cells by passively crossing the membrane down their concentration gradient. The R domain regulates activity further through dynamic phosphorylation at several positions. The movement of chloride ions facilitates the movement of water out of the cell by osmotic pressure and helps keep secretions thin.Cystic fibrosis (CF) arises from recessively inherited mutations in the CFTR gene. The most common mutation is a three-base-pair deletion that removes a phenylalanine residue at position 508 in NBD1 (ΔF508) . This mutation causes the protein to fold incorrectly, making it more susceptible to degradation by proteases. The resulting decrease in CFTR abundance inhibits chloride ion transport, leading to thickening of normally thin secretions and increased risk of life-threatening pulmonary infections.
-According to the information in the passage, which statement best describes the role of ATP in CFTR activity? ATP:

Question

Passage
The cystic fibrosis transmembrane conductance regulator (CFTR) protein is a chloride ion channel involved in the production of mucus, sweat, and digestive fluids. CFTR is composed of five domains (Figure 1) : Two transmembrane domains (TMD1 and TMD2) , two nucleotide binding domains (NBD1 and NBD2) , and one regulatory domain (R domain) .

Figure 1 Schematic diagram of CFTR domainsThe NBD domains regulate CFTR activity by binding ATP, which causes a conformational change in the TMD domains. This change allows chloride ions to leave cells by passively crossing the membrane down their concentration gradient. The R domain regulates activity further through dynamic phosphorylation at several positions. The movement of chloride ions facilitates the movement of water out of the cell by osmotic pressure and helps keep secretions thin.Cystic fibrosis (CF) arises from recessively inherited mutations in the CFTR gene. The most common mutation is a three-base-pair deletion that removes a phenylalanine residue at position 508 in NBD1 (ΔF508) . This mutation causes the protein to fold incorrectly, making it more susceptible to degradation by proteases. The resulting decrease in CFTR abundance inhibits chloride ion transport, leading to thickening of normally thin secretions and increased risk of life-threatening pulmonary infections.
-According to the information in the passage, which statement best describes the role of ATP in CFTR activity? ATP:

Quizplus · Accepted Answer

11ecba2d_0e89_a90f_a3bf_cda47051b5de_MD0008_00 Protein activity can be modulated by interactions with allosteric effectors. Allosteric effectors bind to proteins at one site and cause a change in the shape (conformational change) of the protein at another site, thereby altering its ability to function. Activators increase activity, and inhibitors decrease activity. According to the passage, the binding of ATP to the NBD domains causes a conformational change in a different part of the protein: the TMD domains. This conformational change allows chloride ions to cross the membrane. Because ATP increases the ability of CFTR to carry out its function (chloride transport), ATP acts as an activator. Additionally, ATP binds at a different site on the protein than the site that is affected. Therefore, ATP allosterically activates chloride transport by CFTR. (Choice A) Although ATP binding is necessary for ion transport by CFTR, the passage states that the ions travel passively down their concentration gradient. Energy input from the hydrolysis of ATP is only required for active transport, in which ions travel against their concentration gradient. (Choice B) According to the passage, ATP binds to the NBD domains of CFTR. ATP does not flow through CFTR in either direction. (Choice C) According to the passage, ATP binding facilitates chloride transport by opening the CFTR channel. ATP does not occupy the channel or inhibit transport. Educational objective: Allosteric effectors bind proteins at one site and induce a conformational change (change in shape) at another site. Allosteric activators increase the ability of the protein to function, and inhibitors decrease the function.

Passage the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) Protein Is a a Chloride