BIO130H1 Study Guide - Cell Membrane, Membrane Fluidity, Phospholipid

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26 Apr 2011

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Chapter 10 Membrane Structure
Lecture 1: (pg. 617-624)
Plasma membrane encloses the cell, defines its boundaries, and maintains differences
between the cytosol and extracellular environment
The Lipid Bilayer
-Lipid bilayer provides basic structure for all cell membranes
Phosphoglycerides, Sphingolipids, and Sterols and the Major Lipids in Cell
-50% of animal cell membranes are
o109 lipid molecules in
plasma membrane of small
animal cell
-ALL lipid molecules in cell
membranes are amphiphilic
oHydrophobic water-
fearing nonpolar end
oHydrophilic water-
loving polar end
-Phospholipids polar head group
+ 2 hydrophobic hydrocarbon tails
oOne tail is cis-double
bonded creating a kink in
the tail (unsaturated)
oDifferences in the length
and saturation of fatty acid
tails influence how these molecules pack against one another, affecting the
fluidity of the membrane
- Main phospholipids in most animal cell membranes are phosphoglycerides
o3 carbon glycerol backbone; 2 fatty acids are linked to 2 adjacent carbon
atoms through ester bonds, and 3rd C atom is attached to a phosphate
group, which in turn attaches to other types of head groups
-A combination of different head groups and fatty acids create different
oEg. phoshatidylethanolamine, phosphatidylserine, phosphatidylcholine
-Another important phospholipid is sphingomyelin; built from sphingosine instead
of glycerol
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oLong acyl chain with an amino
group (NH2) and two hydroxyl
groups (OH) at one end
-Lipid bilayers also contain cholesterol
and glycolipids
-Cholesterol is a sterol; contains a rigid
ring structure, to which a polar hydroxyl
group and a short non-polar hydrocarbon
chain is attached
Phospholipids Spontaneously Form Bilayers
-Hydrophilic molecules dissolve in water because they contain charged groups or
uncharged polar groups that form either favourable electrostatic conditions or
hydrogen bonds
-Hydrophobic molecules are insoluble in water because most of their atoms are
uncharged and nonpolar, and cannot form energetically favourable interactions with
water molecules
-From these principles, amphiphilic molecules bury their hydrophobic
hydrocarbon tails in the interior, exposing their hydrophilic heads to
oMicelles spherical shapes; tails inward
oBilayers hydrophobic tails sandwiched between hydrophilic head
-The same forces that drive the formation of bilayers also provide a self-healing
oBreak in a bilayer is energetically unfavourable, so lipids tend to rearrange
spontaneously to eliminate the free edge with water
-Because bilayers must avoid having edges, they close in on themselves creation of
the cell
The Lipid Bilayer Is a Two-dimensional Fluid
-Individual lipid molecules are able to diffuse freely within lipid bilayers
-Liposomes bilayers made in the form of spherical vesicles (25nm-1m in
-Black membranes planar bilayers formed across holes between two aqueous
-Techniques to measure the motion of individual lipid molecules and their
oAttach a fluorescent dye or a small gold particle to a lipid molecules polar
head group and follow the diffusion of individual molecules in a membrane
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