Chapter 7 Membrane Structure and Function Days 8 Objectives -You will understand that membranes are fluid -The structure results in a semi-permeable membrane -Passive transport requires no energy -Active transport requires energy -Bulk transport of molecules either by exocytosis or by endocytosis. Lab 1: Diffusion and Osmosis p. 127

Cell Membranes Are Made up of Macromolecules Lipids -Specifically Phospholipids -Form a bilayer with nonpolar, hydrophobic region in the middle. Proteins -Various proteins are embedded. Carbohydrates -Carbohydrates extend out and old the cell in place to the ECM

Factors That Affect The Fluidity Of The Membrane Cell membranes are mainly held together by nonpolar attractions --- Much weaker then covalent bonds Movement of lipids Saturated Vs Unsaturated fats Cholesterol **Cell Membrane Sidedness P 130

Cellular Proteins Functions: Types: 1. Integral 1. Transport -Hydrophobic Channel -Shuttle uses ATP 2. Enzymes -Use of Active Site -Often grouped together 3. Signal Transduction -Acts in cellular comunication -Uses a receptor site 4. Cell Recognition -Glycoproteins -Immune system 5. Inter Cellular Joining -Used in various types of junctions 6. Attachment proteins -Stablize internal organelles and cell Types: 1. Integral 2. Peripheral Cellular Proteins

Membranes are Selectively Permeable What? Ions (K, Na, Ca, and C Water Sugars Amino Acids Proteins Cellular Respiration To create gradients Why? Maintain homeostasis, balance Protein synthesis Where? Aquaporins allows water to diffuse through Channel proteins (hydrophillic channel) Carrier proteins are specific to what it is moving How? What directs movement? Active transport needs energy Passive transport doesn’t need energy When? When the cell needs anything Constantly

Passive Diffusion: Movement of solutes from a high concentration to a lower concentration. -Takes No Energy to move -In Cell Biology we are talking about movement across the cell membrane Osmosis: Passive diffusion of water. Facilitated Diffusion: Passive diffusion of large solutes through protein channels

Active Transport Passive Transport Takes Energy Increases gradient Gradient is used for cellular work Passive Transport -Takes no energy -Common property of life -The goal is homeostasis

Active Transport Ion pump Co-transport Na/K pump makes use of protein shape and changing ion affinity ATP reacts – Phophate changes shape of protein Membranes can have a electronic potential based on their electrochemical gradient Electrogeneic pump is a membrane protein that increases the electrochemical gradient Ion pump Co-transport -Pump creates a gradient -Use of property of homeostasis to transport large molecules like sucrose

Exocytosis -Transport vesicles inside cell combine with cell membrane and release contents to the exterior of the cell. -Transport occurs along microtubules Endocytosis Phagocytosis Engulf food particles into a food vacuole for digestion Ameobas and pseudopods Pinocytosis is gulping of extracellular fluid Receptor Mediated Endocytosis -Ligands attach to specific -LDL (Low Density Lipoproteins) p. 138