Lecture 4 Notes

Lecture 4 Notes - Lecture 4 Chapter 10 Chapter 10 All...

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Lecture 4 - Chapter 10 Chapter 10 - All biological membranes have a common general structure: each is a very thin film of lipid (fatty) and protein molecules, held together mainly by noncovalent interactions – cell membranes are dynamic, fluid structures, and most of their molecules move about in the plane of the membrane – the lipid molecules are arranged as a continuous double layer about 5 nm thick – this lipid bilayer provides the basic fluid structure of the membrane and serves as a relatively impermeable barrier to the passage of most water- soluble molecules – protein molecules that span the lipid bilayer mediate nearly all of the other functions of the membrane, transporting specific molecules across it, for example, or catalyzing membrane- associated reactions such as ATP synthesis – in the plasma membrane, some transmembrane proteins serve as structural links that connect the cytoskeleton through the lipid bilayer to either the extracellular matrix or an adjacent cell, while others serve as receptors to detect & transducer chemical signals in the cell’s environment – it takes many different membrane proteins to enable a cell to function & interact w its environment, and it is estimated that about 30% of the proteins encoded in an animal cell’s genome are membrane proteins o - Lipid molecules constitute about 50% of the mass of most animal cell membranes, nearly all of the remainder being protein. All of the lipid molecules in cell membranes are amphiphilic – that is, they have a hydrophilic (“water loving”) or polar end and a hydrophobic (“water-fearing”) or nonpolar end. The most abundant membrane lipids are the phospholipids. These have a polar head group and 2 hydrophobic hydrocarbon tails. In animal, plant, and bacterial cells, the tails are usually fatty acids, and they can differ in length (normally contain between 14 and 24 Carbon atoms). One tail typically has one or more cis- double bonds, while the other tail does not. Each cis-double bond creates a small kink in the tail. Differences in the length and saturation of the fatty acid tails influence how phospholipid molecules pack against one another, thereby affecting the fluidity of the membrane. The main phospholipids in most animal cell membranes are the phosphoglycerides, which have a 3-carbon glycerol backbone. 2 long- chain fatty acids are linked through ester bonds to adjacent carbon atoms of the glycerol, and the third carbon is attached to a phosphate group, which in turn is linked to one of several different types of head group.
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o - By combining several different fatty acids and head groups, cells make many different phosphoglyerides. Phosphatidylethanolamine, phosphatidylserine, and phosphatidylcholin are the main ones in mammalian cells. Another important phospholipid, called sphingomyelin, is built from sphingosine rather than glycerol. Sphingosine is a long acyl chain with an amino groups and 2 hydroxyl groups at one end of the molecule. In sphingomyelin, a fatty acid tail is attached to the terminal hydroxyl group, leaving one
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This note was uploaded on 11/22/2010 for the course BIOLGY BICD 110 taught by Professor Yiminzou during the Spring '10 term at UCSD.

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Lecture 4 Notes - Lecture 4 Chapter 10 Chapter 10 All...

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