Lecture 6 (Sept 7)

Lecture 6 (Sept 7) - Biological S nce 110A: I ntroduction...

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Plasma and organelle membranes Structure and properties of phospholipids Properties of the membrane lipid bilayer Structure and properties of sphingolipids Roles of cholesterol in the membrane Asymmetric distribution of lipids in membranes Classes and structure of membrane proteins Biological Sciences 110A: Introduction to Biology Kendal Broadie Reading in Chapter 4 (120-136) Karp
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Plasma membrane of red blood cell All cells are surrounded by a hydrophobic plasma membrane composed primarily of lipids Membranes act as “ semi-permeable barriers ” between the cytoplasm and extracellular environment Membrane receptors sense environmental signals and transduce information into the cell interior Membrane transport machinery allows cell to concentrate substances (sugars, salts (ions), etc.) The membrane scaffolds biochemical reactions , providing a defined space for ordered molecular associations and interactions See Fig. 4.1 Karp
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Eukaryote cells are compartmentalized into many membrane- bound organelles Organelles divide numerous aqueous compartments within the cell Organelles protect the genome and spatially separate transcription, translation and protein modification Organelles sequester “dangerous” metabolic reactions involving enzymatic catalysts that could damage the cell Organelles provide acidic (low pH) chambers used in degradation Organelles provide high [H + ] and [Ca 2+ ] reserves: See Fig. 4.2 Karp
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Primary component of membranes are phospholipids composed of: also called phosphoglycerides owing to glycerol backbone 16-20 carbons See Fig. 4.3 Karp
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The polar head group is variable giving rise to a complex mixture of phospholipids
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Lipids are not soluble in water, spontaneously form “bilayers” Can be dispersed in water as: Micelles: aggregates of 50-100 of lipid molecules with polar heads facing out lipids act as “emulsifying agents:” hydrophobic compounds are sequestered in micelle interior, allowing them to be dispersed in water as an emulsion. This is being developed as a drug delivery system Bilayer membranes: polar heads face water and nonpolar hydrocarbon tails buried in interior. Hydrophilic surfaces, hydrophobic interior H 2 O Lipid molecule Micelle Bilayer membrane ~3 nm See Fig. 4.3 Karp
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Membrane sheets spontaneously close to form “liposomes” Open sheets of membrane are energetically unfavorable…because the hydrophobic lipid tails are exposed to water at the edges. Open sheets spontaneously close to form small
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This note was uploaded on 01/04/2010 for the course BSCI BSCI 110A taught by Professor Zwiebel during the Spring '09 term at Vanderbilt.

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Lecture 6 (Sept 7) - Biological S nce 110A: I ntroduction...

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