You treat some cells with a proteolytic enzyme that is too large to penetrate the cell membrane (Set 1).Another group of cells is made permeable before treatment with the enzyme (Set 2).A third set of cells was not treated with the enzyme at all (controls).Proteins are then extracted from the three different sets of cells and applied to an SDS-PAGE gel.Protein W migrates to the same distance on a gel of proteins from Set 1 and Set 2; Protein W migrates a shorter distance on gels of proteins extracted from the control group than on gels of proteins extracted from Set 1 and Set 2 treated cells.Protein X migrates to the same distance on a gel of proteins from control cells and the gels of the proteins from Set 1 and Set 2.Protein Y migrates a longer distance when extracted from Set 1 cells than does protein Y in the controls; Protein Y moves an even larger distance in the gel of the extracts from Set 2.Protein Z migrates the same distance on gels of proteins from the controls and the proteins extracted from Set 1,but it migrates a longer distance in extracts from Set 2 cells.Which protein is exposed only on the exterior of the cell?
A)Protein W
B)Protein X
C)Protein Y
D)Protein Z
E)Protein K

Question

Quizplus · Accepted Answer

Protein W migrates the same distance on gels of proteins from Set 1 and Set 2, which implies that the proteolytic enzyme did not affect its mobility. However, Protein W migrates a shorter distance on gels of proteins extracted from the control group than on gels of proteins extracted from Set 1 and Set 2 treated cells. This suggests that Protein W is only exposed on the exterior of the cell and is protected from the proteolytic enzyme in Set 1 and Set 2 cells but not in control cells.

You Treat Some Cells with a Proteolytic Enzyme That Is