chapt05_lecture

chapt05_lecture - Membranes Chapter 5 Membrane Structure...

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Membranes Chapter 5
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2 Membrane Structure Phospholipids arranged in a bilayer Globular proteins inserted in the lipid bilayer Fluid mosiac model – mosaic of proteins floats in or on the fluid lipid bilayer like boats on a pond
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5 Cellular membranes have 4 components 1. Phospholipid bilayer Flexible matrix, barrier to permeability 2. Transmembrane proteins Integral membrane proteins 3. Interior protein network Peripheral membrane proteins 4. Cell surface markers Glycoproteins and glycolipids
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6 Both transmission electron microscope (TEM) and scanning (SEM) used to study membranes One method to embed specimen in resin 1µm shavings TEM shows layers
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Freeze-fracture visualizes inside of membrane 7
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8 Phospholipids Structure consists of Glycerol – a 3-carbon polyalcohol 2 fatty acids attached to the glycerol Nonpolar and hydrophobic (“water-fearing”) Phosphate group attached to the glycerol Polar and hydrophilic (“water-loving”) Spontaneously forms a bilayer Fatty acids are on the inside Phosphate groups are on both surfaces
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Bilayers are fluid Hydrogen bonding of water holds the 2 layers together Individual phospholipids and unanchored proteins can move through the membrane 10
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Environmental influences Saturated fatty acids make the membrane less fluid than unsaturated fatty acids “Kinks” introduced by the double bonds keep them from packing tightly Most membranes also contain sterols such as cholesterol, which can either increase or decrease membrane fluidity, depending on the temperature Warm temperatures make the membrane more fluid than cold temperatures Cold tolerance in bacteria due to fatty acid desaturases 11
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12 Membrane Proteins Various functions: 1. Transporters 2. Enzymes 3. Cell-surface receptors 4. Cell-surface identity markers 5. Cell-to-cell adhesion proteins 6. Attachments to the cytoskeleton
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chapt05_lecture - Membranes Chapter 5 Membrane Structure...

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