Chapter 5 - Membrane Structure and Transport

Chapter 5 - Membrane Structure and Transport - MEMBRANE...

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Click to edit Master subtitle style 4/30/11 MEMBRANE STRUCTURE AND TRANSPORT CHAPTER 5
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4/30/11 Biological Membranes Basic framework of the membrane is the phospholipid bilayer Phospholipids are amphipathic molecules Hydrophobic (water-fearing) region faces in Hydrophilic (water-loving) region faces out Membranes also contain proteins and carbohydrates Relative amount of each vary
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4/30/11 Fluid-mosaic model Membrane is considered a mosaic of lipid, protein, and carbohydrate molecules Membrane exhibits properties that resemble a fluid because lipids and proteins can move relative to each other within the membrane
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4/30/11 Proteins bound to membranes Peripheral membrane proteins Noncovalently bound to regions of integral membrane proteins that project out from the membrane, or they are bound to the polar head groups of phospholipids n Integral membrane proteins Transmembrane proteins § One or more regions that are physically embedded in the hydrophobic region of the phospholipid bilayer Lipid anchors § Covalent attachment of a lipid to an amino acid side chain within a protein
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4/30/11 Approximately 25% of All Genes Encode Membrane Proteins Membranes are important biologically and medically Computer programs can be used to predict the number of membrane proteins Estimated percentage of membrane proteins is substantial: 20–30% of all genes may encode membrane proteins This trend is found throughout all domains of life including archaea, bacteria, and eukaryotes Function of many genes unknown- study may provide better understanding and better treatments
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4/30/11 Membranes are semifluid Fluidity- individual molecules remain in close association yet have the ability to readily move within the membrane Semifluid- most lipids can rotate freely around their long axes and move laterally within the membrane leaflet “Flip-flop” of lipids from one leaflet to the opposite leaflet does not occur spontaneously Flippase requires ATP to transport lipids from one leaflet to another
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Factors affecting fluidity Length of fatty acyl tails Shorter acyl tails are less likely to interact, which makes the membrane more fluid Presence of double bonds in the acyl tails Double bond creates a kink in the fatty acyl tail, making it more difficult for neighboring tails to interact and making the bilayer more fluid
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Chapter 5 - Membrane Structure and Transport - MEMBRANE...

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