Download chapter 7 cell membrane

Chapter 7.
The Cell Membrane
AP Biology
Overview
 Plasma membrane separates living cell
from nonliving surroundings

thin barrier = 8nm thick
 Controls traffic into & out of the cell
selectively permeable
 allowing some substances to cross
more easily than others

 Made of phospholipids, proteins & other
macromolecules
AP Biology
Phospholipids
 Fatty acid tails
are hydrophobic
 Phosphate
group form a
hydrophilic head
interaction with
H2O is complex
 & very
important!

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Phospholipids in water
 At surface of a cell phospholipids are
arranged as a bilayer


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hydrophilic heads on the outside in contact with
aqueous solution & hydrophobic tails form core
phospholipid bilayer forms a barrier between
cell & external environment
Fluid Mosaic Model
 In 1972, S.J. Singer & G. Nicolson
proposed that membrane proteins are
inserted into the phospholipid bilayer
AP Biology
A membrane is a collage of different proteins
embedded in the fluid matrix of the lipid bilayer
AP Biology
2004-2005
Membrane Proteins
 Proteins determine most of membrane’s
specific functions
 Plasma membrane & organelle membranes
each have unique collections of proteins
 Membrane proteins:


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peripheral proteins = loosely bound to surface
of membrane
integral proteins = penetrate into lipid bilayer,
often completely spanning the membrane
(a transmembrane protein)
Why are proteins the perfect
molecule to function embedded
in the cell membrane?
AP Biology
2003-2004
AP Biology
Integral Proteins
 Within membrane
hydrophobic regions with nonpolar
amino acids
 often coiled into alpha helices

 Outer surfaces of membrane

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hydrophilic regions
with polar amino
acids
2004-2005
Inside & outside surfaces are different
 2 layers may differ in
lipid composition
proteins in
membrane have a
direction
 outer surface also
has carbohydrates

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2004-2005
Membranes provide a variety of cell functions
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Signal Transduction
 Earl W. Sutherland discovered how the
hormone epinephrine acts on cells
 Sutherland suggested that cells
receiving signals went through three
processes
Reception
 Transduction
 Response

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Cell Signaling – the basics
1- reception
2 - transduction
3 - response
Activation
Of
Cellular
Response
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Fluid membranes
 Permeability

membrane must be fluid, about as fluid
as salad oil
 Changing temperatures
cells alter lipid composition of
membranes
 cold-adapted organisms

 winter wheat increases % unsaturated
phospholipids in autumn
 prevent membranes from solidifying during
winter
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Unsaturated fats
 more fluid membranes

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kinks in unsaturated fatty acid tails
prevent tight packing
Membrane carbohydrates
 Play a key role in cell-cell
recognition
ability of a cell to
distinguish neighboring
cells from another
 important in organ & tissue
development
 basis for rejection of
foreign cells by immune
system

AP Biology
A membrane is a collage of different proteins
embedded in the fluid matrix of the lipid bilayer
AP Biology
2004-2005
Any Questions??
AP Biology
Thanks as
always to Kim
Foglia