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Structure of Plasma Membranes The plasma membrane (also known as the cell membrane or cytoplasmic membrane) is a biological membrane that separates the interior of a cell from its outside environment. The primary function of the plasma membrane is to protect the cell from its surroundings. Composed of a phospholipid bilayer with embedded proteins, the plasma membrane is selectively permeable to ions and organic molecules and regulates the movement of substances in and out of cells. Plasma membranes must be very flexible in order to allow certain cells, such as red blood cells and white blood cells, to change shape as they pass through narrow capillaries. The plasma membrane also plays a role in anchoring the cytoskeleton to provide shape to the cell, and in attaching to the extracellular matrix and other cells to help group cells together to form tissues. The membrane also maintains the cell potential. In short, if the cell is represented by a castle, the plasma membrane is the wall that provides structure for the buildings inside the wall, regulates which people leave and enter the castle, and conveys messages to and from neighboring castles. Just as a hole in the wall can be a disaster for the castle, a rupture in the plasma membrane causes the cell to lyse and die. Fluid Mosaic Model The fluid mosaic model describes the plasma membrane structure as a mosaic of phospholipids, cholesterol, proteins, and carbohydrates. Problem: When scientists at Johns Hopkins University fused human cells with mouse cells that had been dyed blue and red respectively, they made an important breakthrough regarding cell membranes. What was it? A) Cell membranes from mice were very different from those in human cells. B) Human cell membranes did not hold the dye as well. C) The fused cells grew and reproduced pink cells. D) The proteins in the cell membranes were moving around as if in a fluid mosaic. #cytology #cellMembrane #FluidMosaicModel #plasmaMembrane #cytoplasmicMembrane
