TAILIEUCHUNG - Lecture AP Biology - Chapter 7: Membrane structure and function
In this chapter you will learn: Define the following terms: amphipathic molecules, aquaporins, diffusion; explain how membrane fluidity is influenced by temperature and membrane composition; distinguish between the following pairs or sets of terms: peripheral and integral membrane proteins, channel and carrier proteins, osmosis, facilitated diffusion, and active transport, hypertonic, hypotonic, and isotonic solutions. | Membrane Structure and Function What You Must Know: Why membranes are selectively permeable. The role of phospholipids, proteins, and carbohydrates in membranes. How water will move if a cell is placed in an isotonic, hypertonic, or hypotonic solution. How electrochemical gradients are formed. Cell Membrane Plasma membrane is selectively permeable Allows some substances to cross more easily than others Fluid Mosaic Model Fluid: membrane held together by weak interactions Mosaic: phospholipids, proteins, carbs Early membrane model (1935) Davson/Danielli – Sandwich model phospholipid bilayer between 2 protein layers Problems: varying chemical composition of membrane, hydrophobic protein parts The freeze-fracture method: revealed the structure of membrane’s interior Fluid Mosaic Model Phospholipids Bilayer Amphipathic = hydrophilic head, hydrophobic tail Hydrophobic barrier: keeps hydrophilic molecules out Membrane fluidity Low temps: phospholipids w/unsaturated tails (kinks prevent close packing) Cholesterol resists changes by: limit fluidity at high temps hinder close packing at low temps Adaptations: bacteria in hot springs (unusual lipids); winter wheat ( unsaturated phospholipids) Membrane Proteins Integral Proteins Peripheral Proteins Embedded in membrane Determined by freeze fracture Transmembrane with hydrophilic heads/tails and hydrophobic middles Extracellular or cytoplasmic sides of membrane NOT embedded Held in place by the cytoskeleton or ECM Provides stronger framework Integral & Peripheral proteins Hydrophobic interior Hydrophilic ends Some functions of membrane proteins Carbohydrates Function: cell-cell recognition; developing organisms Glycolipids, glycoproteins Eg. blood transfusions are type-specific Synthesis and sidedness of membranes Selective Permeability Small molecules (polar or nonpolar) cross easily (hydrocarbons, hydrophobic molecules, CO2, O2) Hydrophobic core prevents passage of ions, large polar molecules Passive Transport NO ENERGY .
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