TAILIEUCHUNG - Lecture Biology (7th edition) - 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. | Chapter 7 Membrane Structure and Function Overview: Life at the Edge The plasma membrane Is the boundary that separates the living cell from its nonliving surroundings The plasma membrane exhibits selective permeability It allows some substances to cross it more easily than others Figure Concept : Cellular membranes are fluid mosaics of lipids and proteins Phospholipids Are the most abundant lipid in the plasma membrane Are amphipathic, containing both hydrophobic and hydrophilic regions The fluid mosaic model of membrane structure States that a membrane is a fluid structure with a “mosaic” of various proteins embedded in it Membrane Models: Scientific Inquiry Membranes have been chemically analyzed And found to be composed of proteins and lipids Scientists studying the plasma membrane Reasoned that it must be a phospholipid bilayer Figure Hydrophilic head Hydrophobic tail WATER WATER The Davson-Danielli sandwich model of membrane structure Stated that the membrane was made up of a phospholipid bilayer sandwiched between two protein layers Was supported by electron microscope pictures of membranes In 1972, Singer and Nicolson Proposed that membrane proteins are dispersed and individually inserted into the phospholipid bilayer Figure Phospholipid bilayer Hydrophobic region of protein Hydrophobic region of protein Freeze-fracture studies of the plasma membrane Supported the fluid mosaic model of membrane structure Figure A cell is frozen and fractured with a knife. The fracture plane often follows the hydrophobic interior of a membrane, splitting the phospholipid bilayer into two separated layers. The membrane proteins go wholly with one of the layers. Extracellular layer Cytoplasmic layer APPLICATION A cell membrane can be split into its two layers, revealing the ultrastructure of the membrane’s interior. TECHNIQUE Extracellular layer Proteins Cytoplasmic layer Knife Plasma membrane These SEMs show membrane proteins (the “bumps”) in the two .

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