You are working in a laboratory investigating the effects of new chemicals calle

Question

You are working in a laboratory investigating the effects of new chemicals called X and Y that kill cells. To test whether X and Y cause necrosis or apoptosis, you briefly treat cultured cells with each chemical and perform several assays.

Without making the cells permeable in any way, you stain them with Annexin V linked to a green fluorophore, which binds phosphatidylserine, and propidium iodide, which fluoresces red when it binds DNA. Neither of these compounds can travel across intact plasma membranes. During sample preparation you mixed up the samples. Assign a likely identity to the samples in Figure C. Annexin V staining is shown as \ hatching, propidium iodide staining is shown as // hatching, and staining with both in the same region appears as crosshatching. Explain your answer please.

Explanation / Answer

In fig. C, the first panel showing \ hatching indicates Annexin V positive but propidium iodide negative. This explains the process of apoptosis. Because, during apoptosis, the phosphatidylserine externalization is a key factor.

The second panel has no staining. Hence, they are live cells.

The third panel shows \ hatching as well as crosshatching. \ hatching indicates apoptotic cells as in first panel. Whereas crosshatching indicates necrosis as it is both Annexin V positive and propidium iodide positive. During necrosis, the cells get damaged and hence, propidium iodide could enter the cell and stain the DNA.

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