Cells grown in culture are often used to investigate the role of organelles. As culture conditions can be easily manipulated, cells can be subjected to different chemicals and their responses studied and analyzed. In one such experiment, mouse cells were incubated in the presence of high concentrations of sucrose. The cells were examined under the microscope. Crystals of sucrose were found in the lysosomes of all the cells. When sucrose was depleted from the culture medium, the sucrose crystals in the lysosomes persisted for many days, but did not affect the growth of the cells. Eventually, the sucrose crystals disappeared. The rate of disappearance is shown in the graph below (note: all graphs are the same scale).
Researchers performed two additional experiments:
Immediately after sucrose was removed from the culture medium, the enzyme invertase was added. Invertase catalyzes the cleavage of sucrose into monosaccharides. The cells were then examined for the presence of sucrose crystals. The results are shown below.
Mouse cells grown in the presence of invertase (cell type A) were mixed with cells grown in the presence of sucrose (cell type B). A reagent that fuses cells was also added to the culture. After fusion, the cells (cell type AB) were grown in the absence of sucrose. The cells were then examined for the presence of sucrose crystals. The results are shown below.
Based on the results in Experiment 2, which of the following could be true?
I. Invertase diffused from the lysosomes of cell type A into the lysosomes of cell type B.
II. The lysosomes of cell type A fused with the lysosomes of cell type B.
III. Invertase destroyed cell type B and only allowed cell type A to survive.
|C||I and II only|
Either conditions I or II would explain the results seen in Experiment 2. There is no indication that invertase would destroy one cell type, so III is not a possibility.