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2010 Bio 317 Lecture 2

2010 Bio 317 Lecture 2 - BIO 317 Lecture 2 Prof William...

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1 Prof. William Collins Office: 534 Life Sciences Building Office Hours: Mondays, 4:00 – 5:00 PM or by appointment Recommended Reading: Matthews, Chapters 2 & 3 BIO 317: Lecture 2 The Shape and Amphipathic Nature of Phospholipids Gives Them Unique Properties Phospholipids spontaneously form bilayers in an aqueous solution. Phospholipid bilayers spontaneously close to form sealed compartments. Phospholipid bilayers have a self-healing property.
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2 Lipid Molecules Diffuse Freely Within Lipid Bilayers Lipids exhibit rapid movement (e.g., rotation, lateral diffusion) within a monolayer (“leaflet”). However, lipid molecules rarely “flip-flop” from one leaflet to the other. Thus, lipid bilayer membranes are NOT symmetrical!
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3 Lipid Bilayers are Composed of Different Types of Lipids Cholesterol in a Lipid Bilayer Cholesterol molecules orient themselves with their hydroxyl groups close to the polar heads of the phospholipid molecules. The steroid ring region partly immobilizes the first CH 2 groups of the hydrocarbon chains. •Decreases membrane permeability •Decreases membrane fluidity •Inhibits possible phase transitions
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4 Asymmetry of the Lipid Bilayer is Functionally Important Phosphatidylserine is important for binding of protein kinase C to cytosolic surface of plasma membrane. Glycolipids are located exclusively in the noncytosolic leaflet - may play important roles in cell protection and cell recognition. Glycolipid Molecules
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5 Structure of the Plasma Membrane Phospholipid Bilayer Additional components (cholesterol, glycolipids) Properties of lipid bilayer due to the shape and amphipathic nature of phospholipids – Fluidity “Prohibition against free edges” Spontaneous closure to form sealed compartment • Self-healing Effective diffusion barrier against hydrophilic substances Inside and outside leaflets of lipid bilayers are different (asymmetry) However, the bilayer structure alone does not explain how charged substances cross the plasma membrane?
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