Outline Chapter 7 typed

Outline Chapter 7 - CHAPTER 7 MEMBRANE STRUCTURE AND FUNCTION Membranes Basic Structure 6.2.4 o Membrane structural models have evolved as new data

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CHAPTER 7 - MEMBRANE STRUCTURE AND FUNCTION Membranes: Basic Structure – 6.2.4 o Membrane structural models have evolved as new data is acquired. o Earliest models were deduced from indirect evidence 1. Membranes are made of lipid a. Evidence of this: Lipids and lipid-soluble material enter the membrane more quickly than substances which are insoluble in lipids. 2. Phospholipids are amphipathic molecules that can form membranes Amphipathic – A condition where a single molecule has both hydrophilic and hydrophobic regions, meaning that most of the proteins within the membranes have hydrophilic and hydrophobic regions. 3. Cell membranes are phospholipid bi-layers (see fig 7.2) a. Evidence of this: The phospholipid content of red blood cells, which are plasma membranes with no organelles, is just enough to cover the cell with 2 layers. 4. Biological membranes contain proteins. a. This came from the idea that proteins are always in the membrane. b. Evidence: Membranes that are isolated from red blood cells contain proteins in addition to lipids. 5. Biological membranes are coated with proteins that generally absorb water. a. They compared these real membranes to lab-made. b. Evidence: Biological membranes absorb more water on their surfaces than artificial phospholipid membranes. o Davson-Danieli model – the bi-layer was coated on both sides with hydrophilic protiens, and the proteins would’ve been removable but when they attempted, they did not come off. They proposed a sandwich model: a phospholipid bi-layer between two layers of proteins. phospholipid (PL) bilayer globular protein coating
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Hydrophilic zones = polar head groups + globular proteins Hydrophobic zone = 2 x hydrophobic tails about 8 mm thick Confirmed in 1950's Problems with this model: -all membranes are not the same -How do the proteins stay attached? o Singer and Nicolson: FLUID-MOSAIC MODEL (see fig 7.3) proteins embedded in the lipid bi-layer By embedding the proteins in a lipid bi-layer, the proteins cannot get washed away. This model was confirmed by the development of the electron microscope. Hydrophilic zones = polar head groups + hydrophilic portion of proteins Hydrophobic zone = 2 x hydrophobic tails + hydrophobic portion of proteins Confirmed by freeze-fracture and freeze-etch micrographs (see fig 7.4) Cells were frozen ad made thin sections that hit the cells on the edge, peeling the bi-layer sheets apart from one another. The Plasma Membrane: The Fluid Mosaic Model – 7.1.2 o A membrane is a fluid mosaic of lipids, proteins, and carbohydrates. o A membrane is held together mainly by hydrophobic interactions, which are significantly weak. o
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This note was uploaded on 08/29/2010 for the course BIOL 1201 taught by Professor Wishtichusen during the Fall '07 term at LSU.

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Outline Chapter 7 - CHAPTER 7 MEMBRANE STRUCTURE AND FUNCTION Membranes Basic Structure 6.2.4 o Membrane structural models have evolved as new data

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