The Cell Membrane

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.

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

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

Selective Permeability: the cell membrane lets some molecules in and keeps others out 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 Phospholipids Phosphate head Polar Hydrophilic Make up the outer borders of the membrane Glycerol

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

Structure of Phospholipid

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

III.) Structure of Cell Membrane (cont.) Phospholipid Bilayer 2 layers of phospholipids make up a cell membrane 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! 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!

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

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

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

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

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

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

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

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.) 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

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.

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

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.

Arrangement of cell surface proteins

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

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

Cell Membrane Structure Overview