The Cell Membrane

I.) What is the cell membrane? A. AKA: Plasma membrane B. The boundary between the cell and the environment C. 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? 1. Cells breathing 2. Cells getting blood to them 3. 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 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? 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. Polar: positive and negative ends (b/c electrons are not shared equally) 1. Example: Water b. 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?

5. Why are the phospholipids arranged tail to tail? a. Water is inside and outside the cell b. Phosphate group is hydrophilic (polar) end 1. Attracts water c. 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

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

Structure of Cell Membrane (cont.) C.Cholesterol 1. Helps to stabilize the phospholipids and keep them from sticking together

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

Types of proteins (cont.) b. Channel or Pore protein 1. Hydrophilic channel – allows lipid insoluble substances to pass in and out of cell.

Types of proteins (cont.) c. Glycoproteins 1. Protein with what macromolecule attached to it? Carbohydrate Carbohydrate 2. Functions for cell to cell recognition

Types of proteins (cont.) d. Receptor Protein 1. These have binding sites for molecules such as hormones or substrates to bind to

Types of proteins (cont.) e. Enzymatic Protein 1. Catalyze specific reactions along the inside of the cell membrane

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