CH7_outline - 1 2 CH7 Cell Membranes The plasma membrane is...

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1 CH7 – Cell Membranes • The plasma membrane is the boundary that separates the living cell from its surroundings • The plasma membrane exhibits selective permeability, allowing some substances to cross it more easily than others Cellular membranes are fluid mosaics of lipids and proteins • Phospholipids are the most abundant lipid in the plasma membrane • Phospholipids are amphipathic molecules, containing hydrophobic and hydrophilic regions • The FLUID MOSAIC MODEL states that a membrane is a fluid structure with a “mosaic” of various proteins embedded in it The Fluidity of Membranes • Phospholipids in the plasma membrane can move within the bilayer • Most of the lipids, and some proteins, drift laterally • Rarely does a molecule flip-flop transversely across the membrane • As temperatures cool, membranes switch from a fluid state to a solid state • The temperature at which a membrane solidifies depends on the types of lipids • Membranes rich in unsaturated fatty acids are more fluid than those rich in saturated fatty acids • Membranes must be fluid to work properly; they are usually about as fluid as salad oil The affect of cholesterol on the Fluidity of Membranes • The steroid cholesterol has different effects on membrane fluidity at different temperatures • At warm temperatures (such as 37°C), cholesterol restrains movement of phospholipids • At cool temperatures, it maintains fluidity by preventing tight 1 2 3 4 5 6 7 8
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2 packing Membrane Proteins and Their Functions • A membrane is a collage of different proteins embedded in the fluid matrix of the lipid bilayer Illustrated in the FLUID MOSAIC MODEL • Proteins determine most of the membrane’s specific functions • Peripheral proteins are bound to the surface of the membrane • Integral proteins penetrate the hydrophobic core • Integral proteins that span the membrane are called transmembrane proteins • The hydrophobic regions of an integral protein consist of one or more stretches of nonpolar amino acids, often coiled into alpha helices The Extracellular Matrix (ECM) of Animal Cells • Animal cells lack cell walls but are covered by an elaborate extracellular matrix (ECM) • The ECM is made up of glycoproteins such as collagen, proteoglycans, and fibronectin • ECM proteins bind to receptor proteins in the plasma membrane called integrins • Functions of the ECM: Support Adhesion Movement Regulation 9 10 11 12 13 14 15 16 17 18
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3 Intercellular Junctions: Communication between neighboring cells • Neighboring cells in tissues, organs, or organ systems often adhere, interact, and communicate through direct physical contact • Intercellular junctions facilitate this contact • There are several types of intercellular junctions
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This note was uploaded on 07/08/2011 for the course BIOL 101 taught by Professor Smith during the Spring '11 term at Aachen University of Applied Sciences.

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CH7_outline - 1 2 CH7 Cell Membranes The plasma membrane is...

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