Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Lectures by Chris Romero Chapter 7 Membrane Structure and Function
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Overview: Life at the Edge The plasma membrane – Boundary that separates the living cell from its nonliving surroundings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Plasma membrane: selectively permeable – Allows some substances to cross it more easily than others Figure 7.1
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Membrane Models: Scientific Inquiry Membranes have been chemically analyzed – composed of proteins and lipids (1915)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings What Lipids? Scientists studying the plasma membrane – Reasoned that it must be a phospholipid bilayer (1925) Figure 7.2 Hydrophilic head Hydrophobic tail WATER Where are the proteins? -most abundant lipid -amphipathic, Hydrophilic Hydrophobic
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Davson-Danielli sandwich model of membrane structure (1935) – Stated that the membrane was: phospholipid bilayer between two protein layers
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Davson-Danielli sandwich model of membrane structure (1935) – Stated that the membrane was: phospholipid bilayer between two protein layers – Supported by electron microscope pictures of membranes (1950) Figure 7.2 Hydrophilic head Hydrophobic tail WATER
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
In 1972, Singer and Nicolson – Fluid Mosaic Model Figure 7.3 Phospholipid bilayer Hydrophilic region of protein Hydrophobic region of protein
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The fluid mosaic model of membrane structure – A membrane is a fluid structure with a “mosaic” of various proteins embedded in it
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Freeze-fracture studies of the plasma membrane – Supported the fluid mosaic model of membrane structure Figure 7.4
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Membranes are Fluid! Phospholipids in the plasma membrane – Can move within the bilayer Simulation: Dynamic membrane (nhmccd)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Type of hydrocarbon tails in phospholipids – Affects the fluidity
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cholesterol in the membrane How does cholesterol help control membrane fluidity in cold and hot conditions?
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cholesterol in the membrane How does cholesterol help control membrane fluidity in cold and hot conditions? COLD = maintains spaces between tails HOT = prevents tails from moving too much
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Can proteins in the plasma membrane drift within the bilayer? ?
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Can proteins in the plasma membrane drift within the bilayer?
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Membrane Proteins and Their Functions A membrane – Is a collage of different proteins embedded in the fluid matrix of the lipid bilayer
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Integral proteins- Penetrate the hydrophobic core of the lipid bilayer – Transmembrane proteins, completely span membrane EXTRACELLULAR SIDE
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Peripheral proteins – Are appendages loosely bound to the surface of the membrane
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings six major functions of membrane proteins Figure 7.9 Transport Enzymatic activity Signal transduction (a) (b) (c) ATP Enzymes Signal Receptor
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cell-cell recognition. Intercellular joining. Attachment to the cytoskeleton and extracellular matrix (ECM). (d) (e) (f) Glyco- protein Figure 7.9
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 7.2: Membrane structure results in selective permeability A cell must exchange materials with its surroundings controlled by the plasma membrane
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Permeability of the Lipid Bilayer Hydrophobic molecules (nonpolar) Lipid soluble = can pass through the membrane rapidly Ex:? Hydrophilic molecules (polar) Not Lipid soluble = Do not cross the membrane rapidly Ex:?
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Passive transport- diffusion of a substance across a membrane with no energy investment – Diffusion- solute – Osmosis- water
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Diffusion- Tendency for molecules of any substance to spread out evenly into the available space [High] [Low] Molecules of dye Membrane (cross section) Net diffusion Equilibrium
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Substances diffuse down their own concentration gradient (b) Net diffusion Equilibrium
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Effects of Osmosis on Water Balance Osmosis – Is the movement of water across a semi- permeable membrane
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Movement of water – Is affected by the concentration gradient of dissolved substances Figure 7.12 ?
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Movement of water – Is affected by the concentration gradient of dissolved substances Figure 7.12 Osmosis- salt in water
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Behavior of cell in solution without WALLS Tonicity – Ability of a solution to cause a cell to gain or lose water – Has a great impact on cells without walls Hypertonic Hypotonic Isotonic
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings If a the solution is hypertonic – Concentration of solutes is greater than it is inside the cell – The cell will lose water
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings If a the solution is hypotonic – Concentration of solutes is less than it is inside the cell – The cell will gain water
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings If a solution is isotonic – Concentration of solutes is the same as it is inside the cell – There will be no net movement of water
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Facilitated Diffusion: Passive Transport Aided by Proteins Facilitated diffusion – Transport proteins speed the movement of molecules across the plasma membrane – Down their concentration gradient (High Low)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Channel proteins – Provide corridors that allow a specific molecule or ion to cross the membrane Figure 7.15 EXTRACELLULAR FLUID Channel protein CYTOPLASM. (a) Water
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Carrier proteins – Undergo a subtle change in shape Figure 7.15 Carrier protein Solute Glucose (b) Simulate: uniport (nhnccd)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Water balance in cells without walls Isotonic?, Hypertonic?, Hypotonic? A B C
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Water balance in cells without walls Figure 7.13 Hypotonic solution Isotonic solution Hypertonic solution (a) H2OH2O H2OH2O H2OH2O H2OH2O Lysed NormalShriveled
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Water Balance of Cells with Walls Cell walls – Help maintain water balance
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings If a plant cell is turgid – It is in a hypotonic environment – It is very firm, a healthy state in most plants
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings If a plant cell is: Flaccid – It is in an isotonic solution environment Plasmolyzed – It is in a hypertonic solution environment
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Water balance in cells with walls (b) H2OH2OH2OH2O H2OH2O H2OH2O Figure 7.13 Turgid?, Flacid?, Plasmolyzed?
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Concept 7.4: Active transport uses energy to move solutes against their gradients (Low High) = Requires? Ex: sodium-potassium pump
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The sodium-potassium pump High Na+ Low K+ High Na+ Low K+ Na+ Low Na+ High K+ ATP
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings High Na+ Low K+ Na+ K+ P
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings High Na+ Low K+ K+ Exchange 3 Na+ for 2 K+ = net transfer of _________from cytoplasm to extracellular Simulate: ATPase (nhmccd) Low Na+ High K+
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Review: Passive and active transport compared ATP
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 7.5: Bulk transport across the plasma membrane occurs by exocytosis and endocytosis
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 3 types of Endocytosis Figure 7.20 PHAGOCYTOSIS Phagocytosis
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Three types of endocytosis Figure 7.20 PHAGOCYTOSIS Pinocytosis
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Review Ch. 7 Cell Membrane Model 1: Sandwich Describe orientation of phospholipids and proteins Support for model? Model 2: Fluid Mosaic Describe orientation of phospholipids and proteins Support for model?
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Review! Membrane Structure: What makes the membrane fluid? – Movement of phospholipids – Unsaturated vs. saturated FA tails – Cholesterol
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Review Do proteins move in the membrane? Protein types: integral vs. peripheral Membrane Function: – Selectively permeable hydrophilic vs. hydrophobic molecules – Types of transport Passive- NO Energy (E) – Diffusion, osmosis, facilitated
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Review 7: Membrane Function; Transport Passive- NO Energy (E) – Diffusion, osmosis, facilitated Active- Energy (E) – Na+/K+ pump, Electrogenic H+ pump, Cotransporter Bulk transport – Endocytosis vs. Exocytosis Phagocytosis, Pinocytosis, Receptor Mediated
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Hypertonic, Hypotonic, Isotonic? 5 15
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Hypertonic, Hypotonic, Isotonic? 20 15
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings An artificial cell consisting of an aqueous solution enclosed in a selectively permeable membrane has just been immersed in a beaker containing a different solution. The membrane is permeable to water and to the simple sugar glucose and disaccharide sucrose but completely impermeable to fructose. 5M glucose 3M fructose 4M sucrose 6M glucose 2M fructose 1M sucrose