OUTLINE 2c

OUTLINE 2c - OUTLINES FOR BIOLOGY 1201 Section 001 Summer...

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OUTLINES FOR BIOLOGY 1201 Section 001 Summer 2008 DR. STEVEN POMARICO Outline 2B CHAPTER 7 MEMBRANE STRUCTURE AND FUNCTION Membranes: Basic Structure – 6.2.4 >>>>>Membrane structural models have evolved as new data is acquired. Earliest models were deduced from indirect evidence 1. Membranes are made of lipid evidence: lipids and lipid soluble material enter quicker than substances which are insoluble in lipid 2. Phospholipids are amphipathic molecules that can form membranes --- amphipathic a condition where a single molecule has both hydrophilic and hydrophobic regions 3. Cell membranes are phospholipid bilayers (see fig 7.2) Evidence: the phospholipid content of red blood cells is just enough to cover the cell with two layers. The red blood cell has no internal membranes 4. Biological membranes contain proteins Evidence: Membranes isolated from red blood cells contain proteins in addition to lipids 5. Biological membranes are coated with proteins that generally absorb water. Biological membranes absorb more water on their surface than artificial phospholipid membranes
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Davson-Danieli model -phospholipid (PL) bilayer -globular protein coating -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? Singer and Nicolson: FLUID-MOSAIC MODEL (see fig 7.3) -proteins embedded in the lipid bilayer -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) --- Fluid means lateral 2D movement of the lipids and some of the proteins in the plane of the membrane. However, transverse (flip-flop) across the membrane is rare. --- Mosaic means that there are proteins interspersed within the lipid bilayer The Plasma Membrane: The Fluid Mosaic Model – 7.1.2 >>>>>A membrane is a fluid mosaic of lipids, proteins, and carbohydrates. Membranes as a fluid (see fig 7.5) Fluidity is two-dimensional (not three) Factors which influence fluidity of membranes -lipid composition -temperature Proteins as the Mosaic of the Cell Membrane – 7.1.3 Membranes as a Mosaic (see fig 7.6) A mosaic of different proteins are embedded in the lipid bilayer. These proteins have two types of spacial arrangements.
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This note was uploaded on 09/15/2008 for the course BIOL 1201 taught by Professor Wishtichusen during the Summer '07 term at LSU.

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OUTLINE 2c - OUTLINES FOR BIOLOGY 1201 Section 001 Summer...

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