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The Cell Surface Membrane Research Essay.

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The Cell Surface Membrane By Daniel Griffin Introduction The cell surface membrane (also known as the plasma membrane) is a very important structure in both prokaryotic and eukaryotic cells. It surrounds the cell and acts as a boundary between the inside of a cell and its external environment and allows recognition of other external substances (S-cool, n.d.). The Plasma membrane is selectively permeable and therefore controls what substances can enter and exit the cell (ibid). These attributes keep the components of the cell separate from outside cells and helps the cell to maintain homeostasis (ibid). The below diagram shows the fluid mosaic model of membrane structure. Like a mosaic, the cell membrane consists of mny different parts such as proteins, phospholipids, and cholesterol. (Shuster, 2003). The following text aims to detail the key parts of this arrangement and explain how the structure of each part relates to its function. Above: The fluid mosaic model of membrane structure. (Image: Pietzsch, J, 2004) A. Glycosyl-phosphatidylinositol (GPI) B. Proteins C. Carbohydrate D. Cholesterol E. Lipids The Phospholipid Bilayer The Plasma membrane consists of a bilayer of phospholipids. ...read more.


This is where proteins come in; the proteins can be found within the membrane and they regulate the transport of what substances can get into the cell and what can?t (ibid). They act as pumps or channels which open to allow certain substances to come into the cell and close to prevent unwanted particles entering.. This allows bigger charged substances such as glucose to move across (ibid). The lipid bilayer is a fluid and flexible structure. This arrangement allows the structures within the bilayer to be mobile and flow around the cell throughout the plasma membrane (Vision Learning, n.d.). This fluidity is important as it influences membrane transport (ibid). Fluidity is dependent on both the specific structure of the fatty acid chains and temperature (ibid). Structurally, the lipid bilayer is irregular: the lipid and protein arrangement in each of the two layers is different (Shuster, 2003). The Cell Surface & Membrane Proteins The protein and lipid cell membrane is covered with a layer of carbohydrate on the outer surface. ...read more.


In addition to integral proteins there are also less mobile peripheral proteins which attach to the outside of the lipid bilayer (ibid). They are involved in transferring genetic material from one cell to another and are a mechanism which the cell can use to determine what is in its environment (ibid). Above: Membrane proteins. (Image: Gwen V. 1995). A. Carbohydrate group of glycoprotein B. Peripheral protein C. Carbohydrate group of protein D. Carbohydrate group of glycolipid E. Amino acid chain F. Transmembrane proteins Cholesterol One of the most important tasks that cholesterol performs in the body is in cells. Present in animal cell membranes and absent in bacteria and most plants, cholesterol makes the bilayer stronger, more flexible, less fluid, and less permeable to water-soluble substances such as ions and monosaccharide (Vision Learning, n.d.). This helps stabilise the plasma membrane by stopping it from becoming fluid and splitting apart. It also helps to connect phospholipids together and prevents them from drifting apart in warm temperatures or sticking together during cooler temperatures (ibid). Receptors on the outside of the cell seize cholesterol from the bloodstream as needed to keep the cell functioning correctly (ibid). Above: Cholesterol. (Image: Gwen V. 1995). 1. ...read more.

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