Membrane Function Structure and Dynamics Lehninger Readings Chapter 11 pages 371 389 At the end of this section you should be able to apply what you learned about lipids in previous lectures in this course and what you learned about proteins and carbohydrates in BMB461 to discussions about the structure and function of membranes You should be able to explain how interactions between components in the membrane influence the structure and function of the membrane Finally you should be able to predict how the properties and functions of the membranes will change as their compositions changes Student Learning Objectives You should be able to 1 Tell the Big Picture story of how membranes are constructed and how they function 2 Recognize membrane lipids as amphipathic compounds that form lipid bilayers in aqueous media 3 Relate the physical and chemical properties of membrane lipids to their roles in the membrane 4 Describe the functions of membranes in cells and explain how the composition of the membrane and the physical and chemical properties of membrane components relate to those functions 5 Describe the fluid mosaic model of membranes 6 Identify the location orientation and structures of typical lipids and proteins in the asymmetric lipid bilayer 7 Define integral peripheral and lipid anchored membrane proteins and recognize each type in terms of its physical and chemical characteristics 8 Interpret hydropathy plots and relate these to the physical and chemical characteristics of membrane proteins 9 Define membrane fluidity and explain how fluidity is governed by fatty acid composition and cholesterol content relate this to the physical and chemical properties of these molecules and predict how changes in membrane composition will influence fluidity 10 Define lateral and transverse diffusion and explain the diffusion of lipids and proteins in membranes based on their physical and chemical properties 11 Discuss microdomains in membranes including composition and possible biological roles 12 Describe membrane fusion and some biological processes that rely on this feature of membranes Page 1 Membrane Function Structure and Dynamics 1 2 Tell the Big Picture story of how membranes are constructed and how they function Recognize membrane lipids as amphipathic compounds that form lipid bilayers in aqueous media Functions of biological membranes Regulate what crosses the membrane they are semipermeable Transport proteins allow this Demarcate cell boundaries and compartments Organize complex reactions allowing communication and energy generation Receptors proteins are important for perceiving signals The 2D surface increases molecular interactions and increase efficiency Break and reseal allowing things like exocytosis and endocytosis Figure 1 7 Common features despite diversity of biological membranes Membranes are sheet like structures 58 nm 50 80 thick Membrane lipids are amphipathic i e they posses both hydrophobic and hydrophilic components arranged as lipid bilayers Membranes are not covalently assembled but are linked by many noncovalent interactions making the membrane fluid Membranes consist of polar lipids and proteins to which carbohydrates are often attached Membranes are asymmetric Membranes are usually polarized electrically Figure 11 4 Figure 11 3 Page 2 Membrane Function Structure and Dynamics 3 4 Relate the physical and chemical properties of membrane lipids to their roles in the membrane Describe the functions of membranes in cells and explain how the composition of the membrane and the physical and chemical properties of membrane components relate to those functions Lipid Composition Different Organisms Cell Types Different Organelles Figure 11 6 Figure 11 2 Page 3 Membrane Function Structure and Dynamics 5 6 Identify the location orientation and structures of typical lipids and proteins in the asymmetric lipid bilayer Describe the fluid mosaic model of membranes Lipid Composition Inner and Outer Leaflets Fluid Mosaic Model Components Asymmetry Figure 11 5 Movement Lipids can mover laterally with almost no energy input Transversally is high in energy and not common unless with enzyme Asymmetry Figure 11 3 Can split outer layer into two leaflets Outer and inner Page 4 Membrane Function Structure and Dynamics 7 Define integral peripheral and lipid anchored membrane proteins and recognize each type in terms of its physical and chemical characteristics Membrane Proteins Peripheral Sit on surface of membrane Interact with head groups or something Use mild changes i e pH of salt change to remove Integral Defined Have to use harsh treatments to remove protein Asymmetry Figure 11 7 Lipid Protein Interactions Figure 11 11 Figure 11 13 Page 5 Membrane Function Structure and Dynamics 8 Interpret hydropathy plots and relate these to the physical and chemical characteristics of membrane proteins Transmembrane helical Proteins hydropathy plots Figure 11 8 12 Figure 11 10 12 Figure 11 14 Page 6 Membrane Function Structure and Dynamics Fluid Mosaic Model Amphitropic Proteins Sometimes associated with membrane sometimes it is not Lipid Linked Proteins Defined Functions Figure 11 7 Types Fatty acid linkages Isoprenoid linkages GPI linked glycosylated derivatives of phosphatidylinositol Asymmetry Figure 11 15 Page 7 Membrane Function Structure and Dynamics 9 Define membrane fluidity and explain how fluidity is governed by fatty acid composition and cholesterol content relate this to the physical and chemical properties of these molecules and predict how changes in membrane composition will influence fluidity Fluid Mosaic Model Membrane Dynamics Gel vs Fluid State Temperature Lipid Composition Figure 11 16 Regulation of Membrane Fluidity Page 8 Membrane Function Structure and Dynamics 10 Define lateral and transverse diffusion and explain the diffusion of lipids and proteins in membranes based on their physical and chemical properties Fluid Mosaic Model Membrane Dynamics Transverse Diffusion Energetics Transverse Diffusion of Proteins Transverse Diffusion of Lipids Enzyme Catalyzed Movement Figure 11 17 Lateral Diffusion Energetics Figure 11 20 Lateral Diffusion of Proteins Figure 11 19 Lateral Diffusion of Lipids Page 9 Membrane Function Structure and Dynamics 11 Discuss microdomains in membranes including composition and possible biological roles Fluid Mosaic Model Membrane Dynamics Lateral Diffusion of Lipids Sphingolipid Cholesterol Microdomains Rafts Figure 11 20 Composition