You are interested in studying the extracellular binding of proteins to the plas

Question

You are interested in studying the extracellular binding of proteins to the plasma membrane of neuroblastoma cells. You are using fluorescently labeled lectins, which are a class of hydrophilic, membrane-impermeable proteins that bind to carbohydrate molecules. You follow the experimental protocol below. Use a detergent to break up the plasma membrane into small "sheets" without solubilizing/extracting membrane proteins from these "sheets." Remove the detergent, and the "pieces" of plasma membrane spontaneously form small liposomes or vesicles. Apply your fluorescently labeled lectins to the liposomes/vesicles. One of your labmates is surprised that after imaging exactly half of your vesicles are fluorescently labeled. What happened? Assuming you can separate the labeled from unlabeled vesicles, which ones should you keep for further study? Briefly explain why?

Explanation / Answer

A.Plasma membrane is a phospholipid bilayered structure. Hence when they are forming vesicles, only the outer layer is available to the labeled lectin for binding. Also since the labeled lectin is membrane impermeable, it can not label the inner layer. Hence only half of the vesicles are fluorescently labeled.

B. We should keep the unlabled vesicles for further study as they can contain many proteins which carry out important cellular functions like selective transport and cell cell recognition.

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