1. The Cell Membrane

2. I.) What is the cell membrane?
AKA: Plasma membrane
The boundary between the cell and the environment
Does every cell have a cell membrane?
Yes, Each and every cell has a cell membrane.

3. Cell membranes help maintain homeostasis, what is that?
Cells breathing
Cells getting blood to them
Cells maintaining internal conditions
Cells reproducing 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

4. II.) How do cell membranes help to maintain homeostasis?
The cell membrane allows nutrients to come into the cell
Examples: sugar, proteins, fats

5. Selective Permeability: the cell membrane lets some molecules in and keeps others out
The cell membrane removes
waste

6. III.) Structure of the Cell Membrane
What does the cell membrane look like up close?
Lets look at one of these structures up close

7. III.) Structure of Cell Membrane
Phospholipids
Phosphate head
Polar
Hydrophilic
Make up the outer borders of the membrane
Glycerol

8. 2 Fatty acid tails (lipids=fats, oils, etc)
Nonpolar
Hydrophobic
Make up the inner part of the membrane

9. Structure of Phospholipid

10. 4. Why are the phospholipids arranged tail to tail?
Water is inside and outside the cell
Phosphate group is hydrophilic (polar) end
Attracts water
Fatty acid tail end is hydrophobic (nonpolar)
Repels water

11. III.) Structure of Cell Membrane (cont.)
Phospholipid Bilayer
2 layers of phospholipids make up a cell membrane
Remember polar heads and nonpolar tails!

12. 3. Arrangement of phospholipids “tail to tail” due to water inside & outside the cell

13. Let’s Begin to Build Our Membrane!
Take 1 bag with materials for you & your partner
You are going to build your phospholipids first
Marshmallows represent your phosphate head
Toothpicks represent your fatty acid tails
Break these in half. Please include unsaturated fatty acid tails.
Make sure to line up the phospholipid bilayer correctly! Think polar & nonpolar!

14. When something is hydrophilic, it…
Has a chemical makeup that likes to be around water
Has a chemical makeup that does not like to be around water 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

15. Where would you expect to find water in this cell membrane?1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

16. Structure of Cell Membrane (cont.)
Cholesterol
Helps to stabilize the phospholipids and keep them from sticking together

17. Building Time! Now let’s add your cholesterol into the membrane
Use the gummy bears that are in your bags to represent the cholesterol
Be sure to place them correctly
Check with your teacher once your group has completed this
We will stop here for today. Please put your group’s name on the bag and put your phospholipids and cholesterols back in bag

18. Warm Up!
Please put the parts of the cell membrane that we started to build yesterday back together
Phospholipid bilayer
Cholesterols

19. Structure of the Cell Membrane (cont.)
Proteins: Regulate which molecules enter and which molecules leave a cell.

20. Types of proteins in the cell membrane
Carrier Protein
Allow needed substances or waste materials to move through the cell membrane
Molds around the molecule to bring molecule into the cell

21. 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.

22. Types of proteins (cont.)
Channel protein
Hydrophilic channel--allows hydrophilic substances to pass in and out of cell through hydrophobic tails of phospholipids
Allows molecules to easily flow into and out of cell

23. Let’s Build It! 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.

24. Types of proteins (cont. on back)
c. Receptor Protein
These have binding sites for molecules such as hormones or substrates to bind to

25. Let’s Build It! Take your circus peanut out of the bag.
This will represent your receptor protein.
Squish the top of your peanut candy. This will provide the unique shape that will serve as the receptor site.

26. Arrangement of cell surface proteins

27. Structure of Cell Membrane (cont.)
Nonpolar interior zone- true barrier that separates the cell from its surroundings
Many polar particles like sugars, proteins, ions, & most cell wastes cannot cross this zone because they are repelled by the nonpolar region

28. IV.) Fluid Mosaic Model of Cell Membrane
Lipid bilayer is not strong & firm like a hard shell, but it is fluid like a soap bubble
Often called a fluid mosaic model
Individual phospholipids, arranged side by side, float within the bilayer
Cholesterol prevents phospholipids from sticking together

29. Cell Membrane Structure Overview