The Structure of the Cell Membrane

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The Structure of the Cell Membrane
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A soap or detergent molecule will stand on the
surface of still water.
Air
H2O
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Soap molecules form a mono-molecular film on the
surface of water.
Air
H2O
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Agitating soapy water makes micelles.
Agitation of soapy water causes the fatty tails
of soap and detergent molecules to dissolve in
small grease and oil droplets to form micelles.
Each drop of oil is completely surrounded by a
single layer of soap molecules. The more vigorous
the agitation the smaller the micelles. Oil can
be made water soluble and disposable by mixing
with soap or detergent.
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Soap bubbles are made from a double layer of soap
molecules sandwiching a thin layer of water.
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Cell membranes are made of phospholipids.
Phospholipids are very much like soap molecules.
Phospholipids have a charged head that is
hydrophilic and hydrocarbon tails that are
hydrophobic.
Soap
Phospho-lipid
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Phospholipids behave like soap molecules...
Phospholipids will form monomolecular films on
water.
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Gorter and Grendel Data from 1924
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In 1924, Gorter and Grendel suggest that the cell
membrane is a phospholipid bi-layer.
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By the 1930s experimental evidence showed that
proteins were also part of the cell membrane. In
1935, James Danielli and Hugh Davson proposed
the sandwich model a phospholipid bilayer
between two layers of protein.
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Ten years later, electronmicrographs of the cell
membrane provided strong support for the
Danielli-Davson model of the cell membrane.
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However, scanning electron microscopy showed that
proteins did not coat the membrane but were
interspersed throughout the membrane.
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In 1972, Nicolson and Singer presented the fluid
mosaic model of the cell membrane.
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The fluid mosaic model of the cell membrane with
modern details added.
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Assignment 3 The Structure of the Cell Membrane

• Read Section 1.2 Cell Membrane Structure on
  pages 21 -24.
• Answer Questions 1, 2, 5, 6, 7, 8. in the
  Section Review on page 24.