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CHP 11 Biological Membranes and Transport (4pp)

CHP 11 Biological Membranes and Transport (4pp) - Chapter...

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1 Chapter 11 1 Chapter 11 Homework Assignment I have decided to alter the homework assignment for Chapter 11. The following problems will be due once we finish the chapter: 4, 5, 6, 8, 9, 11, 15, 18, 19, 20 Chapter 11 Biological Membranes & Transport Chapter 11 3 The Magic from Lipid Structure: Membranes! Although they comprise a small fraction of the cell’s substituents, membranes fulfill many essential functions: – Compartmental boundaries – Reaction pathway organizers – Cell-cell communication – Selective solute transport – Generate chemical or electrical potentials Good fences make good neighbors - Robert Frost, “Mending Wall” Chapter 11 4 Characteristics of the Lipid Bilayer Amphipathic – hydrophilic exterior, and hydrophobic interior Two molecules thick – 5-8 nm Tough but flexible Can undergo fusion and fission Permeable to nonpolar solutes, but not to polar ones ( why?) Has unique “transition-state” temperature Lateral diffusion is rapid, flip-flop diffusion is slow Composition & Architecture of Membranes
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2 Chapter 11 5 Lipid Components Vary Widely with Function All but about 10% is accounted for by five classes of lipid Phospholipids comprise well over half the lipid of most membranes Many membranes have no cardiolipin Content of cholesterol and sphingolipid varies greatly A Glycerophospholipid Composition & Architecture of Membranes Chapter 11 6 If You Put Lipids into Water… Depending on the shape of the fatty acid(s), you can get micelles, bilayers or liposomes Why do the lipids do this? Chapter 11 7 Real Membranes Are Not Just Static Bilayers They are made asymmetrically, i.e. have an “inside” and an “outside” Proteins exposed on one side of the bilayer are different on the other side of the membrane Melting characteristics are ameliorated by incorporating cholesterol Incorporate a lot of proteins, too ( ratio of lipid:protein ranges from 4:1 to 1:4 ) Beyond being passive barriers, they: Transport ions, solutes, and small molecules Organize energy transduction and biosyntheses Transduce signals from outside to inside Composition & Architecture of Membranes Chapter 11 8 Fluid Mosaic Model ” postulates free lateral motion but restricted transverse mobility Composition & Architecture of Membranes Why is this freedom of movement allowed?
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3 Chapter 11 9 Phospholipid Distribution is Asymmetric Composition & Architecture of Membranes Similar to bilayer proteins, the distribution of phospholipids is also asymmetric The distribution varies depending on the location of the membrane and its biological function Alteration of this distribution can and does have biological consequences For example, exposure of phsophatidylserine on the outer surface marks a cell for destruction via apoptosis Chapter 11 10 Protein Components Also Vary Widely Recall that protein:lipid can range from 1:4 up to 4:1, reflecting functional specialization
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  • Spring '08
  • kore
  • Membranes, Membrane protein, Solute Transport, Biological Membranes & Transport