The Cell Membrane

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

Structure of the cell membrane What does the cell membrane look like up close? What does the cell membrane look like up close? Lets look at one of these structures up close

Structure of Phospholipid

Structure of cell membrane Phospholipids Phospholipids Phosphate head Phosphate head Glycerol Glycerol 2 Fatty acid tails(lipids=fats, oils, etc) 2 Fatty acid tails(lipids=fats, oils, etc)

Polar vs. Nonpolar Polar- positive and negative ends (b/c electrons are not shared equally) Polar- positive and negative ends (b/c electrons are not shared equally) Ex. Water Ex. Water Nonpolar- does not have oppositely charged ends (atoms share electrons equally) Nonpolar- does not have oppositely charged ends (atoms share electrons equally) Which of the above is hydrophilic? Hydrophobic? Which of the above is hydrophilic? Hydrophobic?

Phospholipids 1.) Phosphate Head 1.) Phosphate Head Polar Polar Hydrophilic Hydrophilic Make up the outer borders of the membrane Make up the outer borders of the membrane 2.) Fatty Acid Tails 2.) Fatty Acid Tails Nonpolar Nonpolar Hydrophobic Hydrophobic Make up the inner part of the membrane Make up the inner part of the membrane

Why are the phospholipids arranged tail to tail? - b/c water is inside and outside the cell - b/c water is inside and outside the cell phosphate group is hydrophilic (polar) end phosphate group is hydrophilic (polar) end -attracts water -attracts water fatty acid tail end is hydrophobic (nonpolar) fatty acid tail end is hydrophobic (nonpolar) -repels water -repels water

Structure of cell membrane Phospholipid bilayer Phospholipid bilayer 2 layers of phospholipids make up a cell membrane 2 layers of phospholipids make up a cell membrane

Phospholipid Bilayer Remember polar heads and nonpolar tails Remember polar heads and nonpolar tails

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 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!

Arrangement of phospholipids “tail to tail”

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

When something is hydrophilic, it… 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? 1. Here 2. Here

Other components of the cell membrane Cholesterol Cholesterol Helps to stabilize the phospholipids and keep them from sticking together Helps to stabilize the phospholipids and keep them from sticking together

Building Time! 1. Now let’s add your cholesterol into the membrane 2. Use the gummy bears that are in your bags to represent the cholesterol a. Be sure to place them correctly b. Check with your teacher once your group has completed this

Cell membranes help maintain homeostasis, what is that? 1. Cells breathing 2. Cells getting blood to them 3. Cells maintaining internal conditions 4. Cells reproducing

Other components of the cell membrane Proteins Proteins Regulate which molecules enter and which molecules leave a cell. Regulate which molecules enter and which molecules leave a cell.

Selective Permeability The cell membrane lets some molecules in and keeps others out The cell membrane lets some molecules in and keeps others out

Types of proteins in the cell membrane Channel or Pore protein Channel or Pore protein Hydrophilic channel – allows lipid insoluble substances to pass in and out of cell. Hydrophilic channel – allows lipid insoluble substances to pass in 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 in the cell membrane Carrier Protein Carrier Protein Allow needed substances or waste materials to move through the cell membrane Allow needed substances or waste materials to move through the cell membrane

Let’s Build It! Take your Candy Peanut out of the bag. Take your Candy Peanut out of the bag. This will represent the carrier protein. 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. 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 in the cell membrane Glycoproteins Glycoproteins Protein with what macromolecule attached to it? Protein with what macromolecule attached to it? Carbohydrate Carbohydrate Functions for cell to cell recognition Functions for cell to cell recognition

Let’s Build It! 1. Take the Pretzel Stick out. 2. This will represent the “glyco” part of the glycoprotein. 3. Also take out the large Gum Drop. 4. This will represent the protein part of the glycoprotein

Types of proteins in the cell membrane Receptor Protein Receptor Protein These have binding sites for molecules such as hormones or substrates to bind to These have binding sites for molecules such as hormones or substrates to bind to

Let’s Build It! Take your Fruit Gum Drop out of the bag. Take your Fruit Gum Drop out of the bag. This will represent your receptor protein. This will represent your receptor protein. You will need to use your fingers to “carve out” the active site for this receptor protein You will need to use your fingers to “carve out” the active site for this receptor protein

Types of proteins in the cell membrane Enzymatic Protein Enzymatic Protein Catalyze specific reactions along the inside of the cell membrane Catalyze specific reactions along the inside of the cell membrane

Let’s Build It! Take a scrap sheet of paper and cut out a Pac- Man Shape Take a scrap sheet of paper and cut out a Pac- Man Shape Put this cut-out into your membrane Put this cut-out into your membrane Which way would the protein fit into the membrane? Which way would the protein fit into the membrane? What would fit into Pac-Man’s mouth? What would fit into Pac-Man’s mouth?

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) 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) individual phospholipids, arranged side by side, float within the bilayer (cholesterol prevents phospholipids from sticking together)

Structure of Cell Membrane nonpolar interior zone- true barrier that separates the cell from its surroundings 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 b/c they are repelled by the nonpolar region many polar particles like sugars, proteins, ions, & most cell wastes cannot cross this zone b/c they are repelled by the nonpolar region

Arrangement of cell surface proteins

Cell Membrane Structure

Lets build a cell membrane together online.com/objects/index_tj.asp?objid=AP online.com/objects/index_tj.asp?objid=AP online.com/objects/index_tj.asp?objid=AP online.com/objects/index_tj.asp?objid=AP1101