Tuesday, October 29, 2019
The Plama Membrane Essay Example for Free
The Plama Membrane Essay The plasma membrane exists in all living things for the simple reason that it serves vital functions without which the cell cannot survive.            The plasma membrane is composed primarily of a phospholipid bilayer which is made up of hydrophobic lipid â€Å"tails†that point inwards and hydrophilic phosphate â€Å"heads†that are positioned so that one layer is in contact with the extracellular fluid and the other with the cytosol. The membrane may thus be thought of as the cells â€Å"skin†enclosing and protecting the organelles and the nucleus. The cell (and its components) however, is not cut off from its environment because the plasma membrane is semipermeable, allowing specific substances necessary for the normal functioning of the cell to pass through. Also, embedded in the bilayer are proteins that assist the passage of substances that normally would not be able to pass through by simple diffusion. A good example would be the sodium-potassium pump (Krogh, 2003) which is responsible for the active transport of these ions. Both potassium and sodium need to move up their concentration gradients (into and out of the cell, respectively) and since both are ions that would be difficult to transport through the hydrophobic interior of the bilayer, such transport needs to be facilitated by the use of proteins that will serve as channels through which these ions can pass through. This therefore illustrates as well the regulatory functions of the plasma membrane in that it allows transport into and out of the cell in a selective manner (Postlethwait Hopson, 2006).            Proteins that lie on the surface of the plasma membrane also serve a role in facilitating communication between the cell and its environment, including other cells. Lymphocytes (white blood cells) for example, differentiate foreign cells from that of the body by recognizing antigens, surface-bound proteins that serve as identification for the lymphocyte to know whether the other cell is an invader that needs to be eliminated (Postlethwait Hopson, 2006).            Clearly, the plasma membrane serves critical roles in cellular function, not just in THE PLASMA MEMBRANE                                                                                                                                                   Page # 2 protecting the cell but as well as in transport, regulation and communication, and since, as Krogh (2003) has stated, â€Å"all life is made of cells†, it follows that life simply is not possible without the plasma membrane. References: Krogh, D. (2003). Biology: A Guide to the Natural World, 3rd ed. Companion Website. Retrieved Dec. 31, 2007, from http://wps.prenhall.com/esm_krogh_biology_3/ Postlethwait, J. H., Hopson, J. L. (2006). Modern Biology.                                          Texas: Holt, Rinehart and Winston.
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