Lecture 5 BIO - Lecture 5: Chapter 5 Biological Membranes...

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Lecture 5: C h apter 5 – B i o l og i cal M e mb r an es Cadherins : the principal cell adhesion molecules in vertebrates and in many invertebrates A . P l a s m a m e m brane 1. Physically separates interior of cell from external environment 2. Receives info. about changes in environment 3. Regulates 4. Communicates with other cells 5. Forms compartments to allow separate functions 6. Participates in biochemical reactions **Biological membranes are complex, dynamic structures made of lipid and protein molecules that are in constant motion They regulate the passage of materials, divide the cell into compartments, serve as surfaces for chemical reactions, adhere to and communicate with other cells, and transmit signals between the environment and the interior of the cell The core of cell membrane consists of lipids, mostly phospholipids Phospholipids form bilayers in water - A phospholipids contains two fatty acid chains linked to two of the three carbons of a glycerol molecule - The fatty acid chains make up the non polar hydrophobic (water fearing) portion of the phospholipids. Bonded to the third carbon of the glycerol is a negatively charged , hydrophilic (water loving) phosphate group P l a s m a M e m brane In t egral m e m brane pro t e i ns - embedded in bilayer (not easily removed) - Amphipathic ; hydrophilic heads extend into cytoplasm; hydrophobic regions interact with FA tails of membrane phospholipids - Amphipathic molecules : molecules of this type, which have distinct hydrophobic and hydrophilic regions. - Trans-membrane proteins - extend completely through membrane (as both α helices and ϐ sheets or barrel configuration) - Phospholipids tend to have uniform widths; their roughly cylindrical shapes, together with their ampipathic properties are responsible for bilayers formation. In summary, phospholipids form bilayers because the molecules have (1) two distinct regions, one strongly hydrophobic and the other strongly hydrophilic (making them strongly amphipathic) and (2) cylindrical shapes that allow them to associate with water most easily as bilayers
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F l u i d m o s a i c m odel - cell membranes consist of a fluid bilayer composed of phospholipids in which a variety are embedded or peripheral to it - In 1935, these findings, together with other data, led Davson and Danielli, to propose a model in which they envisioned a membrane as a kind of “sandwich” consisting of a lipid bilayers (double layer of lipid) between two protein layers. - According to their fluid mosaic model : a cell membrane consists of a fluid bilayers of phospholipids molecules in which the proteins are embedded or otherwise associated much like the tiles in a mosaic picture. Li
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This note was uploaded on 11/19/2011 for the course BIOLOGICAL 101 taught by Professor Harry,janes during the Fall '11 term at Rutgers.

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Lecture 5 BIO - Lecture 5: Chapter 5 Biological Membranes...

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