Lecture 3.2 Study Guide – Biological Membranes Assigned Reading: Chapter 6.1; 6.3-6.4 Learning Objectives – At the conclusion of this lecture, you should be able to: • List & explain the functions of biological membranes. • Differentiate between the types of movement that components can exhibit within a membrane. • Describe the fluid mosaic model for biological membranes. • Explain the experimental data that provided evidence for the fluid mosaic model. • Define transition temperature. • List and describe the four factors that affect membrane fluidity. • Predict what changes an organism would make to its membrane composition in response to to a given temperature change. • List and describe the three types of membrane proteins. • Differentiate between passive and active transport mechanisms. • Differentiate between channels, carriers, and pumps. Key Terms You Should Be Able to Use & Apply – • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • Active transport Amphipathic Antiporter Aquaporin Carrier protein Cell fusion Channel protein Cholesterol Concentration gradient Diffusion Electrochemical gradient Equilibrium Facilitated diffusion Flip-flop movement Fluid mosaic model Gated channel BIOSC 0150 (2214)/Gardner 1 Heterokaryon Hypertonic Hypotonic Integral membrane protein Ion channel Isotonic Lateral movement Lipid bilayer Lipid-anchored protein Osmosis Passive transport Peripheral membrane protein Phospholipid Primary active transport Pump Rotational movement Lecture 3.2 Study Guide • • • • • • Secondary active transport Selective permeability Simple diffusion Symporter Transition temperature (Tm) Uniporter Key Concepts You Should Be Able to Use & Apply – • All life consists of cells bounded by membranes composed of lipid bilayers containing amphipathic phospholipids, membrane proteins, and cholesterol. • According to the fluid mosaic model, the plasma membrane is a mosaic of lipids and proteins, which (unless restrained) are free to move laterally within the plane of the membrane. • Cell fusion experiments by Frye & Edidin revealed the mobility of membrane proteins. • Membrane fluidity is affected by temperature, the saturation and length of hydrocarbon tails, and cholesterol. • The main types of membrane proteins are integral membrane proteins, peripheral membrane proteins, and lipid anchored proteins, which differ in their affinity for the hydrophobic interior of the membrane. Transmembrane proteins serve a variety of cellular functions. • Selective permeability allows the membrane to determine what substances enter or leave a cell or organelle. • Substances cross biological membranes by passive or active transport processes. Passive transport is diffusion of a substance across a membrane that may or may not rely on the assistance of a transmembrane protein. Protein pumps perform active transport using energy. Examples of Skills You Should Be Able to Demonstrate – • Predict how changes in environment and/or lipid composition will affect membrane fluidity. • Describe how cell fusion can be used to study the movement of a protein, and be able to make predictions, interpret the data and make conclusions from such an experiment. • Identify which type of membrane protein a given protein is based on its amino acid composition and/or orientation within a membrane. • Predict whether a given molecule would be permeable across a selectively permeable membrane. • Predict which way a certain substance will diffuse, given its concentration on either side of a selectively permeable membrane. BIOSC 0150 (2214)/Gardner 2 Lecture 3.2 Study Guide • Given concentration gradient(s) across a membrane, identify whether an ion/molecule will move by passive or active transport and what type of protein will be used to facilitate movement. Recommended Chapter Questions – • • • • • 5.1 Recap: Question 2. 6.1 Recap: Questions 1-4 (NOTE: ignore the freeze-fracture portion of question 3). 6.3 Recap: Questions 1, 3. 6.4 Recap: Questions 1-2, 4. Figure Questions: Figure 6.1. Additional Practice Problems – 1. Complete each statement with the correct Key Term: A. ____________________ comprise the major lipid component of biological membranes, where membrane formation is a consequence of the ____________________ nature of the molecules. B. The ____________________ is a molecular model for the structure of biological membranes consisting of a fluid phospholipid bilayer in which suspended proteins are free to move in the plane of the bilayer. C. ____________________ are at least partially embedded in the plasma membrane, where ____________________ are associated with but not embedded within the plasma membrane. D. ____________________ is the process of random movement toward a state of equilibrium. E. There are two fundamentally different processes by which substances cross biological membranes: ____________________ processes do not require the input of chemical energy to drive them, where ____________________ processes are driven by chemical energy. F. ____________________ involves a transport system coupled to an exergonic chemical reaction (most commonly the hydrolysis of ATP). ____________________ involves the coupled transport of two substances: one down its concentration gradient and the other against its concentration gradient. 2. Describe the energetic driving force for the formation of a phospholipid bilayer. BIOSC 0150 (2214)/Gardner 3 Lecture 3.2 Study Guide 3. Why does membrane fluidity matter? What happens if a membrane becomes too rigid? … too fluid? 4. It is very rare for a phospholipid in the outer leaflet of a bilayer to spontaneously flip to the inner leaflet of a bilayer. Why? What is a positive consequence of this lack of flip-flop movement for the cell’s membrane? 5. Consider a plant cell’s phospholipid bilayer membrane. Determine the ways that the plant cell’s membranes might accommodate for the following changes in temperature by assigning each outcome (a-e) to a corresponding temperature change. Increase in environmental temperature a. b. c. d. e. Decrease in environmental temperature Increase the quantity of unsaturated fatty acids in the membrane. Increase the quantity of saturated fatty acids in the membrane. Convert the unsaturated fatty acid tails from cis to trans conformations. Lengthen the hydrocarbon tails. Shorten the hydrocarbon tails. 6. Saline solution is a 0.9% solution of NaCl in water, and is injected directly into the bloodstream to treat dehydration. Why is pure water not injected into the bloodstream to treat dehydration? BIOSC 0150 (2214)/Gardner 4 Lecture 3.2 Study Guide 7. Transport mechanisms for the movement of materials across a membrane are depicted below. Match each label to the correct term. A term may be used more than once. A L K M Movement along the concentration gradient J H F C B G D I E _____ Active transport _____ Against _____ Carrier _____ Channel _____ Down _____ Energy _____ Facilitated diffusion _____ High concentration _____ Low concentration _____ Passive transport _____ Pump _____ Simple diffusion BIOSC 0150 (2214)/Gardner 5 Lecture 3.2 Study Guide 8. You have prepared two different sets of liposomes, which are small, spherical phospholipid-bilayer enclosed structures with an aqueous interior. Set A lacks transmembrane proteins altogether, while set B contains a variety of transporters and ion channels. You prepare these liposomes such that the interior of the liposome is topologically equivalent to the extracellular space, and the outside is topologically equivalent to the cytoplasm. A. What general types of molecules can pass into each type of liposome? B. Liposomes in set B contain the K+ channel, which transports K+ down its concentration gradient. You can monitor movement into and out of the liposomes using a radioactive isotope of K+. You can also adjust the K+ concentrations inside and outside of the liposome. Under what conditions will you see radioactive K+ flow into the liposomes? …out of the liposomes? 9. The figure below shows the concentrations of three ions on the inside and outside of a cell, as well as the direction of transport of each through a membrane protein. Which ion(s) is/are moved by active transport and why? BIOSC 0150 (2214)/Gardner 6 Lecture 3.2 Study Guide Lecture 3.2 – Biological Membranes Lecture 3.2.1 Reading: Chapter 6.1; 6.3-6.4 The Fluid Mosaic Model Learning Objectives: • List & explain the functions of biological membranes. • Differentiate between the types of movement that components can exhibit within a membrane. • Describe the fluid mosaic model for biological membranes • Explain the experimental data that provided evidence for the fluid mosaic model. Kathryn Gardner, Ph.D. BIOSC 0150 (2214) 1 2 Cells contain each of the four macromolecules image from: H.T. Jansen, et al. Communications Biology 2:336 (2019) 3 image from: P. Raven, et al. Biology, 10th ed. (2014) 4 All life consists of cells bounded by membranes composed of lipid bilayers Fibers of extracellular matrix (ECM) Biological membranes have many functions Carbohydrate Lipids Glycoprotein Cholesterol Peripheral protein Integral protein Microfilaments of cytoskeleton 5 adapted from FIGURE 6.1 All life consists of cells bounded by membranes composed of lipid bilayers image from: G. Karp. Cell and Molecular Biology: Concepts & Experiments, 7th ed. (2013) 6 Phospholipids are the most common lipid found in biological membranes Example of a PHOSPHOLIPID – choline* Fibers of extracellular matrix (ECM) Carbohydrate phosphate glycerol Lipids Glycoprotein Cholesterol Peripheral protein Integral protein Microfilaments of cytoskeleton fatty acids adapted from FIGURE 6.1 7 image from: J.B. Reece, et al. Campbell Biology, 10th ed. (2013) 8 A lipid bilayer spontaneously assembles in an aqueous environment to minimize the energy of the system According to the FLUID MOSAIC MODEL, a membrane is a fluid bilayer of lipids with a mosaic of associated proteins 9 FIGURE 6.2 Membranes must be fluid to work properly FIGURE 6.9 image from: J. Hardin & G.P. Bertoni. Becker’s World of the Cell, 9th ed. (2015) 10 Membranes components (unless restrained) can move within the membrane 11 image from: J. Hardin & G.P. Bertoni. Becker’s World of the Cell, 9th ed. (2015) 12 Cell fusion experiments by Frye & Edidin revealed the mobility of membrane proteins Cell fusion experiments by Frye & Edidin revealed the mobility of membrane proteins H-2 Fluorescent dye time Antibody Heterokaryon Draw what you would predict to see in the microscope if proteins laterally diffuse. Human 13 image from: L.D. Frye & M. Edidin. J. Cell Science 7:319-335 (1970) Mouse 14 TOPHAT L3.2 Q1 Frye & Edidin followed the movement of proteins at the cell’s equator 15 16 TOPHAT L3.2 Q2 Lecture 3.2.2 Membrane Fluidity Learning Objectives: • Define transition temperature. • List and describe the four factors that affect membrane fluidity. • Predict what changes an organism would make to its membrane composition in response to a given temperature change. 17 Fluidity affects membrane permeability and the ability of membrane proteins to move to where their function is needed In-Text Art, p. 111 19 18 Membrane fluidity changes with temperature image from: J. Hardin & G.P. Bertoni. Becker’s World of the Cell, 9th ed. (2015) 20 Chain length and saturation affect the Tm of a membrane image from: J. Hardin & G.P. Bertoni. Becker’s World of the Cell, 9th ed. (2015) CHOLESTEROL acts as a fluidity buffer 21 image from: J. Hardin & G.P. Bertoni. Becker’s World of the Cell, 9th ed. (2015) 22 Let’s Think About That! Let’s Think About That! To begin, first complete LaunchPad Activity 6.2/Lipid Bilayer Composition Simulation (www.life11e.com/ac6.2). How would the cell membrane composition of each of the following animals compare to that of a counterpart animal @ 25°C? A. A hibernating hedgehog whose environment is 5°C. More saturated fatty acids. More unsaturated fatty acids. More short-tail fatty acids. More long-tail fatty acids. More cholesterol. Less cholesterol. B. A warm-blooded tropical fish whose environment is 35°C. More saturated fatty acids. More unsaturated fatty acids. More short-tail fatty acids. More long-tail fatty acids. More cholesterol. Less cholesterol. 23 24 TOPHAT L3.2 Q3 TOPHAT L3.2 Q4 25 TOPHAT L3.2 Q5 26 TOPHAT L3.2 Q6 27 28 All life consists of cells bounded by membranes composed of lipid bilayers Lecture 3.2.3 Transmembrane Proteins Fibers of extracellular matrix (ECM) Carbohydrate Learning Objectives: Lipids Glycoprotein • List and describe the three types of membrane proteins. Cholesterol 29 31 Integral protein Microfilaments of cytoskeleton 30 adapted from FIGURE 6.1 Membrane proteins differ in their affinity for the hydrophobic interior of the membrane and therefore the extent to which they interact with the lipid bilayer image from: J. Hardin & G.P. Bertoni. Becker’s World of the Cell, 9th ed. (2015) Peripheral protein Integral membrane proteins are amphipathic FIGURE 6.16 32 TOPHAT L3.2 Q7 Functions of transmembrane proteins Signaling molecule Enzymes ATP Receptor Signal transduction Glycoprotein image adapted from: J.B. Reece, et al. Campbell Biology, 10th ed. (2013) 33 TOPHAT L3.2 Q8 34 TOPHAT L3.2 Q9 35 36 Biological membranes have many functions Lecture 3.2.4 Transport Across Membranes Learning Objectives: • Differentiate between passive and active transport mechanisms. • Differentiate between channels, carriers, and pumps. 37 Selective permeability allows the membrane to determine what substances enter or leave a cell or organelle TABLE 6.1 image from: G. Karp. Cell and Molecular Biology: Concepts & Experiments, 7th ed. (2013) 38 DIFFUSION is the process of random movement toward a state of equilibrium 39 In-Text Art, p. 118 40 PASSIVE TRANSPORT is diffusion of a substance across a membrane Osmosis is the diffusion of water across membranes lipid bilayer image from: S. Freeman, et al. Biological Science, 5th ed. (2013) 41 PASSIVE TRANSPORT can involve either of two types of diffusion image from: J. Hardin & G.P. Bertoni. Becker’s World of the Cell, 9th ed. (2015) 42 FIGURE 6.10 An AQUAPORIN is a channel protein through which water can move 43 image from: A.S. Verkman, M.O. Anderson & M.C. Papadopoulos. Nature Reviews Drug Discovery 13:259-277 (2014). 44 GATED CHANNELS are proteins that open/close in response to a specific stimulus, allowing for the flow of ions and small molecules to be carefully regulated Unlike channel proteins, CARRIER PROTEINS do not form a pore but instead undergo structural changes to move substances during the process of facilitated diffusion GLUT-1 45 FIGURE 6.11 FIGURE 6.12 46 ACTIVE TRANSPORT is the movement of ions or molecules across a membrane against an electrochemical gradient Animation 6.1 47 image from: J. Hardin & G.P. Bertoni. Becker’s World of the Cell, 9th ed. (2015) 48 Pumps (i.e., transport ATPases) perform active transport image from: J. Hardin & G.P. Bertoni. Becker’s World of the Cell, 9th ed. (2015) Active transport is directional 49 PRIMARY ACTIVE TRANSPORT: Energy from ATP is used to move Na+ and K+ against their concentration gradients by the sodium-potassium pump (Na+/K+-ATPase) 51 FIGURE 6.13 50 SECONDARY ACTIVE TRANSPORT: The movement of Na+ down its concentration gradient drives the transport of glucose against its concentration gradient FIGURE 6.15 52 TOPHAT L3.2 Q10 Animation 6.2 53 TOPHAT L3.2 Q11 54 TOPHAT L3.2 Q12 55 56 TOPHAT L3.2 Q13 TOPHAT L3.2 Q14 57 TOPHAT L3.2 Q15 58 TOPHAT L3.2 Q16 59 60 TOPHAT L3.2 Q17 TOPHAT L3.2 Q18 61 TOPHAT L3.2 Q19 62 TOPHAT L3.2 Q20 63 64 65