15-44 Fibroblast cells from patients W, X, Y, and Z, each of whom has a different
inherited defect, all contain “inclusion bodies,” which are lysosomes filled with
undigested material. You wish to identify the cellular basis of these defects. The
1. a defect in one of the lysosomal hydrolases
2. a defect in the phosphotransferase that is required for mannose-6-
phosphate tagging of the lysosomal hydrolases
3. a defect in the mannose-6-phosphate receptor, which binds mannose-6-
phosphate-tagged lysosomal proteins in the trans Golgi network and
delivers them to lysosomes
When you incubate some of these mutant fibroblasts in a medium in which
normal cells have been grown, you find that the inclusion bodies disappear.
Because of these results, you suspect that the constitutive exocytic pathway in
normal cells is secreting lysosomal hydrolases that are being taken up by the
mutant cells. (It is known that some mannose-6-phosphate receptor molecules are
found in the plasma membrane and can take up and deliver lysosomal proteins via
the endocytic pathway.) You incubate cells from each patient with medium from
normal cells and medium from each of the other mutant cell cultures, and get the
results summarized in Table Q15-44.
Indicate which defect (1, 2, 3) each patient (W, X, Y, Z) is most likely to have.
This question was answered on: May 23, 2022
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