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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This note was uploaded on 06/03/2008 for the course BIO 150 taught by Professor Kore during the Spring '08 term at Abraham Baldwin Agricultural College.

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

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