Chapter 7- Plasma Membrane

Chapter 7- Plasma Membrane - 1/19/2010 ThePlasmaMembrane...

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1/19/2010 1 The Plasma Membrane © 2010: D. Julian The plasma membrane is a boundary 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. © 2010: D. Julian Phospholipids are amphipathic Phospholipids are the most abundant lipid in the plasma membrane. Phospholipids are amphipathic molecules , containing hydrophobic and hydrophilic regions. Hydrophilic head WATER Hydrophobic tail WATER © 2010: D. Julian
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1/19/2010 2 Fluid mosaic model The fluid mosaic model states that a membrane is a fluid structure with a “mosaic” of various proteins embedded in it. Phospholipid bilayer © 2010: D. Julian 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 fluidity: phospholipid movement Lateral movement (~10 7 times per second) Flip-flop (~ once per month) (a) Movement of phospholipids Fluid Viscous membrane. (b) Membrane fluidity Unsaturated hydrocarbon tails with kinks Saturated hydro- carbon tails (c) Cholesterol within the animal cel membrane Cholesterol © 2010: D. Julian 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 Membrane fluidity: temperature Lateral movement (~10 7 times per second) Flip-flop (~ once per month) (a) Movement of phospholipids Fluid Viscous lipids. Membranes rich in unsaturated fatty acids are more fluid that those rich in saturated fatty acids. (b) Membrane fluidity Unsaturated hydrocarbon tails with kinks Saturated hydro- carbon tails (c) Cholesterol within the animal cel membrane Cholesterol © 2010: D. Julian
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1/19/2010 3 The steroid cholesterol has different effects on membrane fluidity at different temperatures. At warm temperatures (such as 37°C), cholesterol Lateral movement (~10 7 times per second) Flip-flop (~ once per month) (a) Movement of phospholipids Fluid Viscous Membrane fluidity: cholesterol restrains movement of phospholipids. At cool temperatures, it maintains fluidity by preventing tight packing. (b) Membrane fluidity Unsaturated hydrocarbon tails with kinks Saturated hydro- carbon tails (c) Cholesterol within the animal cel membrane Cholesterol © 2010: D. Julian Peripheral and integral proteins Peripheral proteins: bound to membrane surface. Integral proteins: penetrate the hydrophobic core . Fibers of extracel ular matrix (ECM) Glyco- Carbohydrate protein Microfilaments of cytoskeleton Cholesterol Peripheral proteins Integral protein CYTOPLASMIC SIDE OF MEMBRANE Glycolipid EXTRACELLULAR SIDE OF MEMBRANE © 2010: D. Julian Transmembrane proteins Integral proteins that span the membrane are called transmembrane proteins. The hydrophobic regions consist of one or more
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Chapter 7- Plasma Membrane - 1/19/2010 ThePlasmaMembrane...

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