CellBio4 - Membranes and the Internal Membrane System...

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Membranes and the Internal Membrane System Chapter 5
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Functional Properties of Cell Membranes Semi-permeable phospholipid bilayer barriers that prevent passage of some molecules from one side to the other, and permit passage of others Selective Permeability
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Figure 5.2 A Phospholipid Bilayer Separates Two Aqueous Regions Lipid like olive oil
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Figure 3.20 Phospholipids (A) Repeat Fig 3.20A here
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Lipids maintain a bilayer organization spontaneously Membranes contain proteins, the number and types of proteins varies with cell function
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Figure 5.1 The Fluid Mosaic Model
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There are three kinds of membrane transport mechanisms How do the necessary molecules get across membranes ?
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Membrane Transport Mechanisms 1) Simple Passive Diffusion permits crossing of molecules that can dissolve in (thus, penetrate) the membrane the molecules equilibrate across the membrane, they do not become concentrated on either side they can move in either direction
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Molecules that diffuse across cell membranes: water (because of its small size- passes through imperfections in the lipid bilayer) lipids lipid-soluble small molecules
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Molecules that do not diffuse across cell membranes : Most water-soluble molecules Molecules carrying positive or negative charges sugars, amino acids, proteins, peptides, nucleic acids If such molecules cross membranes, they must do it in highly specialized ways
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The Three Membrane Transport Mechanisms 1) Simple Passive Diffusion (No energy needed)
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The Three Membrane Transport Mechanisms 1) Simple Passive Diffusion (No energy needed) 2) Carrier (Receptor)-Mediated Diffusion (no energy) Transported molecules bind to receptors or carriers in the membrane that help transport the molecule Can transport in either direction
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Figure 5.12 A Carrier Protein Facilitates Diffusion (Part 1) Glucose binding site No ATP Required
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Figure 5.12 A Carrier Protein Facilitates Diffusion (Part 2)
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Watch Diffusion movie Animation 05-01
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Membrane Transport Mechanisms 1) Passive Diffusion (can transport in both directions) 2) Carrier-Mediated (Facilitated) Diffusion (can transport in both directions) 3) Active (ATP-dependent) Transport is unidirectional Carriers use ATP to pump molecules against a concentration gradient
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Energy-Dependent Channels are Classifed as Uniports Antiports Symports
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Uniports, Symports, Antiports Uniports: transport one substance in one direction Symports: transport two different substances in the same direction Antiports: transport two different substances in opposite directions
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Figure 5.13 Three Types of Proteins for Active Transport
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Additional Important Concepts about Transport Systems Transport can be Primary or Secondary
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With Primary Active Transport- all of the energy comes from Hydrolysis of ATP, even when two molecules are transported
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Figure 5.14 Primary Active Transport: The Sodium–Potassium Pump
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With Primary Active Transport- all of the energy comes from Hydrolysis of ATP, even when two molecules are transported
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This note was uploaded on 10/16/2010 for the course MCDB MCDB 1A taught by Professor Senghuilow during the Spring '09 term at UCSB.

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CellBio4 - Membranes and the Internal Membrane System...

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