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Course: MCAT > Unit 2

Lesson 1: Foundation 1: Biomolecules

Gene expression: Investigating families with hormone deficiencies


Hormone A is a protein that induces normal cells to release more chloride ions (Cl) into the extracellular space. To examine the mechanism of Hormone A, researchers screened hundreds of families for inherited deficiencies in Hormone A-induced calcium release. They found two unrelated families in which many males, but no females, had a defect in their ability to respond to Hormone A.
The researchers performed a series of experiments on cells isolated from affected males and unaffected females from each of the families. They wanted to determine: (A) the mechanism that related the binding of Hormone A and Cl release in a normal cell, and (B) the point in the mechanism where the defect occurs in affected males. They obtained the following results:
•In both families, none of the cell isolates from affected males had an elevated efflux of Cl after the addition of Hormone A.
•Hormone A was bound to Protein X of all of the isolated cells examined.
•Protein X was smaller than normal in cells from affected males in Family 1, but its size was normal in all other cells examined.
•In whole cells, Protein X phosphorylated Protein Y in the cells of females only.
•When Protein X was isolated in its active form from females, it phosphorylated Protein Y isolated from the affected males of Family 1, but not Family 2.
•Phosphorylated Protein Y was necessary and sufficient to increase the rate of Cl efflux in cells isolated from females.
Based on the passage, what does the mutation in the gene for affected males from Family 2 most likely result in?
Choose 1 answer: