A soap molecule has a long hydrocarbon chain
and a charged head. Soap will form a monomolecular film on water.
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
hydrocarbon chain
air
charged head
C
C
C
C
C
C
C
C
C
C
water
Agitating soapy water makes micelles.
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
H3C
CH3
CH
3
CH
CH33
CH3
CH3
CH3
CH3
CH
CH33
CH3
H3H
CC
C
CH
CH
CH
3 CH
3
H
C3
H
C
3
3
3
H
C
3
H
C
3
H3C
H3C
H3C
H3C
H
3C
H
C
H
3
3C
CH
CH3 3
CH
3
3
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
water
Soap bubbles are made from a double layer of soap
molecules sandwiching a thin layer of water.
CH3
CH3
CH3
CH 3
CH3
CH 3
CH 3
CH 3
CH 3
H3C
CH3
H 3C
CH 3
C
C
H 3C
C
C
C
C
C
C
C
C
H 3C
C
C
C
CH 3
C
C
C
C
C
C
C
C
CH 3
C
H 3C
C
C
C
C
C
C
CH3
C
C
H 3C
C
C
C
C
C
H 3C
CH3
CH
3
CH
CH33
CH 3
CH3
CH 3
CH 3
CH
CH33
CH 3
H 3H
CC
H 3C
C
C
C
H3C
H 3C
H 3C
H 3C
C
C
H 3C
HC3C
H
H
33C
CH
CH 3 3
CH
3
3
C
CH 3
C
CH
CH
CH
3 CH
33
H
C3C3
H
3
H
CC
3H
3
CH 3
C
C
C
C
C
C
CH3
C
H 3C
C
C
C
C
C
C
C
C
H3C
CH 3
C
C
C
C
C
C
C
C
H 3C
C
C
CH3
C
C
C
C
C
C
C
C
C
CH 3
H 3C
CH 3
H 3C
CH3
H 3C
CH 3
H3C
H 3C
H3C
H 3C
H 3C
H 3C
H 3C
Phospholipids, the main component of cell membranes,
behave like soap molecules.
CHCH
3 3
CHCH
3 3
CHCH
3 3
CHCH
3 3
CHCH
3 3
CHCH
3 3
CHCH
3 3
CHCH
3 3
CHCH
3 3
CHCH
3 3
hydrophobic tails
air
hydrophilic head
C C
C C
C C
C C
C C
C C
C C
C C
C C
C C
water
Introduction
 A thin outer layer called the cell membrane surrounds all cells.

1.
2.
3.
4.
This membrane has four main functions:
allow the transport of raw materials into the cell
allow the transport of manufactured products and wastes out of the cell
prevent the entry of unwanted material into the cell
prevent the leakage of essential matter out of the cell
Introduction
 Cellular functions depend on a watery environment
like the one that is found on the inside of the cell.
 In order to maintain their integrity, cells need to be
surrounded by an environment through which water
cannot flow. A membrane composed of fatty
molecules serves this purpose.
History of the Cell Membrane
 In 1924, using an
electron microscope, two
Dutch physicians, E.
Gorter and F. Grendel
found that the cell
membrane was
composed primarily of
phospholipids (shown
on the right).
History of the Cell Membrane
 They deduced, based on the
properties of phospholipids,
that the cell membrane was in
fact a bilayer.
water of the cytoplasm
C C
CH
CHCH
3
CH
33 3
C C
C C
CH
CHCH
3
CH
33 3
C C
C C
C C
CH3
CHCH
CH
33 3
C C
CH3
CHCH
CH
33 3
C C
C C
CH
CHCH
3
CH
33 3
C C
C C
CH
CHCH
3
CH
33 3
C C
C C
CH
CHCH
3
CH
33 3
C C
C C
CH3
CHCH
CH
33 3
C C
C C
CH
CHCH
3
CH
33 3
C C
C C
CH
CHCH
3
CH
33 3
C C
water of the extra-cellular fluid
History of the Cell Membrane
 Cell membranes form because
these phospholipid molecules
spontaneously orient themselves
in a double layer having a fatty
inside and a water soluble outside.
water of the cytoplasm
C C
CH
CHCH
3
CH
33 3
C C
C C
CH
CHCH
3
CH
33 3
C C
C C
C C
CH3
CHCH
CH
33 3
C C
CH3
CHCH
CH
33 3
C C
C C
CH
CHCH
3
CH
33 3
C C
C C
CH
CHCH
3
CH
33 3
C C
C C
CH
CHCH
3
CH
33 3
C C
C C
CH3
CHCH
CH
33 3
C C
C C
CH
CHCH
3
CH
33 3
C C
C C
CH
CHCH
3
CH
33 3
C C
water of the extra-cellular fluid
History of the Cell Membrane
 Phospholipids are made up
of a glycerol backbone with
a hydrophilic head region
containing a phosphate
group and a hydrophobic
tail region containing a
saturated fatty acid and an
unsaturated fatty acid.
 The fact that it has both
types of fatty acids ensures
the cell membrane is fluid.
History of the Cell Membrane
 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 with pores for
molecules to travel
through.
History of the Cell Membrane
 Stronger electron microscopes would show that the
cell membrane was not covered in protein, but rather
had protein embedded in it.
History of the Cell Membrane
 In 1972, S. J. Singer and Garth Nicholson presented
the fluid mosaic model of the cell membrane, which
displayed the cell membrane as an integration of
proteins and other molecules into the phospholipid
bilayer.
Structures in the Fluid Mosaic
Model of the Cell Membrane
 Cholesterol is
interspersed throughout
the cell membrane to
add rigidity to it.
 It also allows the cell
membrane to stay fluid
over a wider range of
temperatures.
Structures in the Fluid Mosaic
Model of the Cell Membrane
 Various proteins are associated with the cell membrane.
1. Integral Proteins (a.k.a. trans-membrane proteins)
span the width of the cell membrane and create
channels through which charged molecules or large
molecules can pass through.
2. Peripheral Proteins are found on the surface of the cell
membrane and are primarily used in cell to cell
signaling with surface carbohydrate chains or linking
with the cytoskeleton for support.
Structures in the Fluid Mosaic
Model of the Cell Membrane
 The cytoskeleton is
attached to the cell
membrane for added
stability, since
membrane proteins and
phospholipids can shift
places in the membrane.
The Fluid Mosaic Model