The Cell
Membrane
I.) What is the cell membrane?
A.
B.
C.
AKA: Plasma membrane
The boundary between the cell and the
environment
Does every cell have a cell membrane?
1.
Yes, Each and every cell has a cell membrane.
Cell membranes help maintain
homeostasis, what is that?
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Cells getting blood
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Cells maintaining
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Cells reproducing
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II.) How do cell membranes help to
maintain homeostasis?
A.
The cell membrane allows nutrients to
come into the cell
1. Examples: Glucose, amino acids, lipids
B. Selective Permeability: the cell
membrane lets some molecules in and
keeps others out
C. The cell membrane removes
waste
III.) Structure of the Cell Membrane

What does the cell membrane look like up close?
Lets look at one
of these
structures up
close
III.) Structure of Cell Membrane
A. Phospholipids
1. Phosphate head
a. Polar
b. Hydrophilic
c. Make up the outer borders of the
membrane
2. Glycerol
3.
2 Fatty acid tails
(lipids=fats, oils, etc)
a. Nonpolar
b. Hydrophobic
c. Make up the inner part
of the membrane
Structure of Phospholipid
4. Polar vs. Nonpolar
a.
b.

Polar: positive and negative ends (b/c
electrons are not shared equally)
1.
Example: Water
Nonpolar: does not have oppositely
charged ends (atoms share electrons
equally)
Which of the above is hydrophilic?
Hydrophobic?
5. Why are the phospholipids arranged
tail to tail?
a.
b.
c.
Water is inside and outside the cell
Phosphate group is hydrophilic (polar)
end
1.
Attracts water
Fatty acid tail end is hydrophobic
(nonpolar)
1.
Repels water
III.) Structure of Cell Membrane
(cont.)
B. Phospholipid Bilayer
1. 2 layers of phospholipids make up a cell
membrane
2. Remember polar heads and nonpolar tails
3. Arrangement of phospholipids “tail to tail”
due to water inside & outside the cell
Let’s Begin to Build Our Membrane!
1.
2.
Take 1 bag with materials for you & your partner
You are going to build your phospholipids first
a. Marshmallows represent your phosphate head
b. Toothpicks represent your fatty acid tails
1. Break these in half. Please include
unsaturated fatty acid tails.
c.
Make sure to line up the phospholipid
bilayer correctly! Think polar & nonpolar!
When something is hydrophilic, it…
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2.
Has a chemical
makeup that likes to
be around water
Has a chemical
makeup that does
not like to be around
water
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1.
Where would you expect to find water in
this cell membrane?
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Structure of Cell Membrane (cont.)
C. Cholesterol
1. Helps to
stabilize the
phospholipids
and keep
them from
sticking
together
Building Time!
1.
2.
Now let’s add your cholesterol
into the membrane
Use the gummy bears that are in your bags to
represent the cholesterol
a.
b.
Be sure to place them correctly
Check with your teacher once your group has
completed this
Structure of the Cell Membrane
(cont.)
D. Proteins: Regulate which molecules enter
and which molecules leave a cell.
1. Types of proteins in the cell
membrane
a.
Carrier Protein
1. Allow needed substances or waste materials
to move through the cell membrane
Let’s Build It!


Take out the paper Pac-Man Shape
Put this cut-out into your membrane
Which way would the protein fit into the membrane?
 What would fit into Pac-Man’s mouth?
 How will this Pac-Man carrier protein work?

Types of proteins (cont.)
b.
Channel or Pore protein
1.
Hydrophilic channel – allows lipid insoluble
substances to pass in and out of cell.
Let’s Build It!
1.
2.
3.
Take the Twizzler out of your bag.
This represents the channel protein.
You will need to split this in half in order
to represent both sides of the channel.
Types of proteins (cont.)
c.
Glycoproteins
1. Protein with what
macromolecule attached to it?
Carbohydrate
2. Functions for cell to cell recognition
Let’s Build It!
1.
2.
3.
4.
Take the Pretzel Stick out.
This will represent the “glyco” part of the
glycoprotein.
Also take out the large Gum Drop.
This will represent the protein part of the
glycoprotein
Types of proteins (cont.)
d.
Receptor Protein
1. These have binding sites for molecules
such as hormones or substrates to bind to
Let’s Build It!
Take your 2 hard candies out of the bag.
 These will represent your receptor protein.
 You will need to place them end-to-end so
they will go from the outside surface of the
membrane to the inside surface of the
membrane.

Types of proteins (cont.)
e.
Enzymatic Protein
1. Catalyze specific reactions along the inside
of the cell membrane
Let’s Build It!


Take your Candy Peanut out of the bag.
This will represent the enzymatic protein.

Keeping in mind what we just talked about in class,
think of a way you can turn this into what an
enzymatic protein is.
Arrangement of cell surface proteins
Structure of Cell Membrane (cont.)
E. Nonpolar interior zone- true barrier
that separates the cell from its
surroundings
1. Many polar particles like sugars,
proteins, ions, & most cell wastes
cannot cross this zone b/c they are
repelled by the nonpolar region
IV.) Fluid Mosaic Model of Cell
Membrane
A. Lipid bilayer is not strong & firm like a
hard shell, but it is fluid like a soap
bubble
1. Often called a fluid mosaic model
B. Individual phospholipids, arranged side
by side, float within the bilayer
1. Cholesterol prevents phospholipids
from sticking together
Cell Membrane Structure Overview