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Lec5notescomplete - Bio1A Dr. McCray Lec 5 Complete Notes 1...

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Bio1A Dr. McCray Lec 5 Complete Notes 1 Chapter 7 Membrane Structure and Function Plasma Membrane Á The plasma membrane is the boundary that separates the living cell from its nonliving surroundings Á The plasma membrane exhibits selective permeability , allowing some substances to cross it more easily than others Fluid mosaics Á Phospholipids are the most abundant lipid in the plasma membrane Á Phospholipids are amphipathic molecules, containing hydrophobic and hydrophilic regions Á The fluid mosaic model states that a membrane is a fluid structure with a “mosaic” of various proteins embedded in it Fig. 7-2, Fig. 7-3 Studying the Plasma Membrane Á Freeze-fracture studies of the plasma membrane supported the fluid mosaic model Á Freeze-facture is a specialized preparation technique that splits a membrane along the middle of the phospholipid bilayer Fig. 7-4 The Fluidity of Membranes Á Phospholipids in the plasma membrane can move within the bilayer Á Most of the lipids, and some proteins, drift laterally Á Rarely does a molecule flip-flop transversely across the membrane Fig. 7-5a Consistency of Membranes Á As temperatures cool, membranes switch from a fluid state to a solid state Á The temperature at which a membrane solidifies depends on the types of lipids Á Membranes rich in unsaturated fatty acids are more fluid that those rich in saturated fatty acids Á Membranes must be fluid to work properly; they are usually about as fluid as salad oil Fig. 7-5b Cholesterol in Membranes Á The steroid cholesterol has different effects on membrane fluidity at different temperatures Á At warm temperatures (such as 37°C), cholesterol restrains movement of phospholipids Á At cool temperatures, it maintains fluidity by preventing tight packing Fig. 7-5c
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Bio1A Dr. McCray Lec 5 Complete Notes 2 Membrane Proteins Á Some proteins in the plasma membrane can drift within the bilayer Á Proteins are much larger than lipids and move more slowly Á To investigate whether membrane proteins move, researchers fused a mouse cell and a human cell Fig. 7-6 Membrane Proteins and Their Functions Á A membrane is a collage of different proteins embedded in the fluid matrix of the lipid bilayer Á Proteins determine most of the membrane’s specific functions Á Peripheral proteins are not embedded Á Integral proteins penetrate the hydrophobic core and often span the membrane
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This note was uploaded on 09/16/2010 for the course BIO 1A taught by Professor Mccray during the Fall '09 term at Merritt College.

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Lec5notescomplete - Bio1A Dr. McCray Lec 5 Complete Notes 1...

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