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The Cell Membra
ne
I.) What is the cell membrane?
A. AKA: Plasma membraneB. The boundary between the cell and
the environmentC. 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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1. Cells breathing2. Cells getting
blood to them3. Cells
maintaining internal conditions
4. Cells reproducing
II.) How do cell membranes help to maintain
homeostasis?A. The cell membrane allows
nutrients to come into the cell1. Examples: sugar, proteins,
fats
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.Phospholipids1. Phosphate head
a. Polarb. Hydrophilicc. Make up the outer borders
of the membrane2. Glycerol
3. 2 Fatty acid tails (lipids=fats, oils, etc)
a. Nonpolarb. Hydrophobicc. Make up the
inner part of the membrane
Structure of Phospholipid
4. Why are the phospholipids arranged tail to tail? a. Water is inside and outside the
cell b. Phosphate group is hydrophilic
(polar) end1. Attracts water
c. Fatty acid tail end is hydrophobic (nonpolar)
1. Repels water
III.) Structure of Cell Membrane (cont.)
B. Phospholipid Bilayer1. 2 layers of phospholipids make up
a cell membrane2. 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. Take 1 bag with materials for you & your partner
2. You are going to build your phospholipids firsta. Marshmallows represent your
phosphate headb. Toothpicks represent your fatty acid
tails1. 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…
Has
a c
hemic
al m
ake.
.
Has
a c
hemic
al m
ake.
.
6%
94%1. Has a chemical makeup that likes to be around water
2. Has a chemical makeup that does not like to be around water
Where would you expect to find water in this cell
membrane?
Her
e H
ere
6%
94%1. Here2. Here
Structure of Cell Membrane (cont.)
C.Cholesterol1. Helps to
stabilize the phospholipids and keep them from sticking together
Building Time!1. Now let’s add your cholesterol
into the membrane2. Use the gummy bears that are in
your bags to represent the cholesterol
a. Be sure to place them correctlyb. Check with your teacher once your
group has completed this
3. We will stop here for today. Please put your group’s name on the bag and put your phospholipids and cholesterols back in bag
Bell Work
1. Please put the parts of the cell membrane that we built yesterday back together
a. Phospholipid bilayerb. Cholesterols
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 Protein1. Allow needed substances or
waste materials to move through the cell membrane
2. Molds around the molecule to bring molecule into the cell
Let’s Build It!
Take your Pretzel Twist out of the bag.
This will represent the carrier protein. Keeping in mind what we just talked
about in class, think of a way you can turn this into what a carrier protein is.
Types of proteins (cont.)
b. Channel protein1. Hydrophilic
channel--allows hydrophilic substances to pass in and out of cell through hydrophobic tails of phospholipids
2. Allows molecules to easily flow into and out of cell
Let’s Build It!
1. Take the Twizzler out of your bag.
2. This represents the channel protein.
3. You will need to split this in half in order to represent both sides of the channel.
Types of proteins (cont.)
d. Receptor Protein1. These have binding sites for
molecules such as hormones or substrates to bind to
Let’s Build It!
Take your 2 hard fruit candies out of the bag.
This will represent your receptor protein.
Leave the wrapper on! This will provide the unique shape that will serve as the receptor site.
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 because 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