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explain the structure and function of plasma
membrane with the help of a labelled diagram.
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Answer:
Explanation:
The cell membrane is the outermost layer of the cell that surrounds the complete contents of a cell, including the endoplasmic reticulum, nucleus, cytoplasm, mitochondria, and all other organelles. It consists of a phospholipid bilayer and the integral proteins which provide pathways for the molecules to move through the membrane. In the animal cell, these cell membrane acts as the barrier between the inner contents of the cell and the external environment. The main function of a cell membrane includes, regulation of entry and exits within the cell, provides shape to the cell and ensures that the cell organelles do not flow away from the cell.
Answer:
Explanation:
Like all other cellular membranes, the plasma membrane consists of both lipids and proteins. The fundamental structure of the membrane is the phospholipid bilayer, which forms a stable barrier between two aqueous compartments. In the case of the plasma membrane, these compartments are the inside and the outside of the cell. Proteins embedded within the phospholipid bilayer carry out the specific functions of the plasma membrane, including selective transport of molecules and cell-cell recognition.
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The Phospholipid Bilayer
The plasma membrane is the most thoroughly studied of all cell membranes, and it is largely through investigations of the plasma membrane that our current concepts of membrane structure have evolved. The plasma membranes of mammalian red blood cells (erythrocytes) have been particularly useful as a model for studies of membrane structure. Mammalian red blood cells do not contain nuclei or internal membranes, so they represent a source from which pure plasma membranes can be easily isolated for biochemical analysis. Indeed, studies of the red blood cell plasma membrane provided the first evidence that biological membranes consist of lipid bilayers. In 1925, two Dutch scientists (E. Gorter and R. Grendel) extracted the membrane lipids from a known number of red blood cells, corresponding to a known surface area of plasma membrane. They then determined the surface area occupied by a monolayer of the extracted lipid spread out at an air-water interface. The surface area of the lipid monolayer turned out to be twice that occupied by the erythrocyte plasma membranes, leading to the conclusion that the membranes consisted of lipid bilayers rather than monolayers.
The bilayer structure of the erythrocyte plasma membrane is clearly evident in high-magnification electron micrographs (Figure 12.1). The plasma membrane appears as two dense lines separated by an intervening space—a morphology frequently referred to as a “railroad track” appearance. This image results from the binding of the electron-dense heavy metals used as stains in transmission electron microscopy (see Chapter 1) to the polar head groups of the phospholipids, which therefore appear as dark lines. These dense lines are separated by the lightly stained interior portion of the membrane, which contains the hydrophobic fatty acid chains.