Cell Bio NOTES

Cell Bio NOTES - various notes and collations including a...

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DIFFUSION AND FACILITATED DIFFUSION_ Diffusion in Biological Systems Diffusion is the movement of molecules from an area of high concentration to an area of lower concentration. However, biological systems may contain barriers that inhibit diffusion. For example, cell membranes contain fat (the lipid bilayer) which will prevent non-fat-soluble substances, carbohydrates and proteins, from diffusing into the cell even though a concentration gradient exists. Thus, cells have developed mechanisms, such as facilitated diffusion, to enhance the transport of non-fat-soluble molecules. Facilitated Diffusion Some molecules, such as those that are soluble in water, cannot pass through the phospholipids in the bilayer. They are transported across the membrane by carrier proteins. A carrier protein will have a specific binding site for the substance it transports. Solute molecules moving about on either side of the membrane will randomly come into contact with their specific binding site. Once they bind, the protein changes shape and the molecules come off the binding site on the other side of the membrane. No energy is used in the process of facilitated diffusion. Facilitated diffusion is simply diffusion involving a protein to make diffusion happen more easily across a cell membrane.
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ACTIVE TRANSPORT The process of active transport is complex and can be difficult to understand. It is, however, an important process to understand in regard to nutrition as many nutrients use this process for absorption. Hopefully, this step-by-step guide along with the illustrations in the presentation window will help. It will be a lot easier for you to understand if you try not to get involved with the technical physiology and chemistry. Try just to understand the overall concepts. 1. Sucrose is broken down by an enzyme on the intestinal cellmembrane. 2. Glucose needs the help of sodium to get into the intestinal cell; Why?: A. The concentration of glucose is greater on the inside of the cell than in the intestinal lumen. That is, glucose is going “up” the concentration gradient (i.e., hard to get in). B: The concentration of sodium is greater on the outside compared to the inside of the cell. Sodium is going “own” the concentration gradient (i.e., easy to get in). 3. The glucose concentration of the intestinal cell builds up until it’_ concentration is greater than the blood. Once this occurs than glucose “diffuses” into the blood and off to the liver. 4.
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This note was uploaded on 08/25/2009 for the course BIO 315 taught by Professor Steiner during the Spring '08 term at Kentucky.

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Cell Bio NOTES - various notes and collations including a...

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