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Membrane Structure and Function Slide 1 ___________________________________ Chapter 7 Membrane Structure and ___________________________________ Function ___________________________________ PowerPoint® Lecture Presentations for Biology Eighth Edition Neil Campbell and Jane Reece ___________________________________ Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings ___________________________________ ___________________________________ ___________________________________ Slide 2 Overview: The Membrane Barrier ___________________________________ • The plasma membrane is the boundary that separates the living cell from its surroundings ___________________________________ • All eukaryotic membranes exhibit selective permeability, allowing some substances to cross them more easily than others ___________________________________ Membrane Channel Protein ___________________________________ Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings ___________________________________ ___________________________________ ___________________________________ Slide 3 Concept 7.1: Cellular membranes are fluid mosaics ___________________________________ of lipids and proteins • Phospholipids are the most abundant lipid in membranes • Phospholipids are amphipathic molecules, containing ___________________________________ hydrophobic and hydrophilic regions The fluid mosaic model ___________________________________ states that a membrane is a fluid structure with a “mosaic” of various proteins embedded in it ___________________________________ Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings ___________________________________ ___________________________________ ___________________________________ Slide 4 Fig. 7-5 ___________________________________ The Fluidity of Membranes Lateral movement Flip-flop Most of the (~107 times per second) (~ once per month) lipids, and (a) Movement of phospholipids some proteins, ___________________________________ Fluid Viscous drift laterally Unsaturated hydrocarbon Saturated hydro- tails with kinks carbon tails Rarely does a ___________________________________ (b) Membrane fluidity molecule flip-flop transversely across the membrane ___________________________________ Cholesterol (c) Cholesterol within the animal cell membrane ___________________________________ ___________________________________ ___________________________________ Slide 5 Fig. 7-6 ___________________________________ Demonstration of Protein Drift in a Membrane RESULTS ___________________________________ Membrane proteins Mixed proteins ___________________________________ after 1 hour Mouse cell Human cell Hybrid cell ___________________________________ ___________________________________ ___________________________________ ___________________________________ Fig. 7-5b Slide 6 •Membranes rich in unsaturated fatty acids are more ___________________________________ fluid that those rich in saturated fatty acids •Membranes must be fluid to work properly; they are usually about as fluid as salad oil ___________________________________ Fluid Viscous ___________________________________ Unsaturated hydrocarbon Saturated hydro- ___________________________________ tails with kinks carbon tails ___________________________________ ___________________________________ ___________________________________ Slide 7 Fig. 7-5c ___________________________________ •The steroid cholesterol has different effects on membrane fluidity at different temperatures •At warm temperatures (such as 37°C), cholesterol restrains movement of phospholipids ___________________________________ •At cool temperatures, it maintains fluidity by preventing tight packing ___________________________________ ___________________________________ Cholesterol ___________________________________ ___________________________________ ___________________________________ Slide 8 Fig. 7-7 ___________________________________ Fibers of extracellular matrix (ECM) ___________________________________ Glyco- Carbohydrate protein Glycolipid EXTRACELLULAR SIDE OF MEMBRANE ___________________________________ Transmembrane protein Cholesterol Peripheral Proteins provide most proteins Integral membrane-specific protein ___________________________________ CYTOPLASMIC SIDE functions OF MEMBRANE ___________________________________ ___________________________________ ___________________________________ Slide 9 Fig. 7-8 ___________________________________ N-terminus EXTRACELLULAR SIDE What types ___________________________________ of side chains are on outside of ___________________________________ these helices? C-terminus CYTOPLASMIC α Helix SIDE ___________________________________ ___________________________________ ___________________________________ ___________________________________ Slide 10 Fig. 7-9ac ___________________________________ Signaling molecule Enzymes Receptor ___________________________________ ___________________________________ ATP Signal transduction (a) Transport (b) Enzymatic activity (c) Signal transduction ___________________________________ ___________________________________ ___________________________________ ___________________________________ Slide 11 Fig. 7-9df ___________________________________ Glyco- ___________________________________ protein (d) Cell-cell recognition (e) Intercellular joining (f) Attachment to the cytoskeleton ___________________________________ and extracellular Carbohydrates often play important roles matrix (ECM) on the plasma membrane. Covalently bonded to lipids (forming glycolipids) or more commonly to proteins (forming glycoproteins) ___________________________________ ___________________________________ ___________________________________ ___________________________________ Fig. 7-10 ER Slide 12 1 ___________________________________ Membranes Transmembrane have glycoproteins Secretory distinct protein inside and The Glycolipid asymmetrical outside distribution of ___________________________________ Golgi 2 faces apparatus proteins, lipids, and Vesicle carbohydrates is determined when the ___________________________________ membrane is 3 built by the ER Plasma membrane: and Golgi Cytoplasmic face 4 apparatus Extracellular face Transmembrane Secreted glycoprotein ___________________________________ protein Membrane glycolipid ___________________________________ ___________________________________ ___________________________________ Slide 13 Selective Permeability ___________________________________ • A cell must exchange materials with its surroundings and compartmentalize its interior. ___________________________________ • This process is controlled by the membranes. • Membranes are selectively permeable, regulating the cell’s molecular traffic ___________________________________ • What does “Selective Permeability” mean? _______________________________________ ___________________________________ Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings ___________________________________ ___________________________________ ___________________________________ Slide 14 The Permeability of the Lipid Bilayer ___________________________________ Hydrophobic (nonpolar) molecules, such as hydrocarbons, can dissolve in the lipid bilayer and pass through the membrane rapidly ___________________________________ estradiol testosterone ___________________________________ Charged or strongly polar molecules, such as ions, ___________________________________ sugars and proteins, do not cross the membrane easily glucose proteins Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings ___________________________________ ___________________________________ ___________________________________ Slide 15 ___________________________________ Some small molecules, even if polar, can pass through the lipid bilayer - very slowly...... ___________________________________ -oxygen -carbon dioxide -urea ___________________________________ -water ___________________________________ H2O ___________________________________ ___________________________________ ___________________________________ Slide 16 Diffusion: True or False ___________________________________ 1. Diffusion requires that the membrane be permeable to the substance that is diffusing 2. Diffusion is spontaneous and passive – requiring no Energy ___________________________________ 3. A substance moves against its concentration gradient during diffusion 4. The concentration of one substance can affect the diffusion of another 5. Diffusion occurs because populations of molecules move randomly, but individual molecules can be directional (moving in a particular direction across a membrane) ___________________________________ 6. Diffusion results from thermal motion (heat) 7. Osmosis is the diffusion of a solute across a selectively-permeable membrane. ___________________________________ 8. At dynamic equilibrium, as many molecules cross in one direction across the membrane as in the other direction ___________________________________ ___________________________________ ___________________________________ Fig. 7-11 Slide 17 Membrane (cross section) ___________________________________ one solute WATER ___________________________________ Net diffusion Net diffusion Equilibrium Net diffusion ___________________________________ two solutes Net diffusion Net diffusion Equilibrium ___________________________________ Net diffusion Net diffusion
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