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The Cell Membrane. 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

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The Cell Membrane

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The Cell Membrane


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


How do cell membranes help to maintain homeostasis?

  • The cell membrane allows nutrients to come into the cell

    • Glucose, amino acids, lipids

  • The cell membrane removes waste


  • Selective Permeability

    • The cell membrane lets some molecules in and keeps others out

    • EX. A cell is low on glucose so the membrane lets in some glucose, but does not overfill the cell with the macromolecule.


    Structure of the cell membrane

    • What does the cell membrane look like up close?

    Lets look at one of these structures up close


    Structure of cell membrane

    • Phospholipids

      • Phosphate head

      • Glycerol

      • 2 Fatty acid tails(lipids=fats, oils, etc)


    Phospholipids

    • 1.) Phosphate Head

      • Polar

      • Hydrophilic

      • Make up the outer borders of the membrane

  • 2.) Fatty Acid Tails

    • Nonpolar

    • Hydrophobic

    • Make up the inner part of the membrane


  • Structure of Phospholipid


    Polar vs. Nonpolar

    Polar- positive and negative ends (b/c electrons are not shared equally)

    Ex. Water

    Nonpolar- does not have oppositely charged ends (atoms share electrons equally)


    Why are the phospholipids arranged tail to tail?

    -b/c water is inside and outside the cell

    phosphate group is hydrophilic (polar) end

    -attracts water

    fatty acid tail end is hydrophobic (nonpolar)

    -repels water


    Structure of cell membrane

    • Phospholipid bilayer

      • 2 layers of phospholipids make up a cell membrane


    Phospholipid Bilayer

    • Remember polar heads and nonpolar tails


    Arrangement of phospholipids “tail to tail”


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


    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


    Where would you expect to find water in this cell membrane?

    • Here

    • Here


    Other components of the cell membrane

    • Cholesterol

      • Helps to stabilize the phospholipids and keep them from sticking together


    Other components of the cell membrane

    • 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


    Types of proteins in the cell membrane

    • Channel or Pore protein

      • Hydrophilic channel – allows lipid insoluble substances to pass in and out of cell.


    Types of proteins in the cell membrane

    • Glycoproteins

      • Protein with what macromolecule attached to it?

        • Carbohydrate

      • Functions for cell to cell recognition


    Types of proteins in the cell membrane

    • Receptor Protein

      • These have binding sites for molecules such as hormones or substrates to bind to


    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)


    Structure of Cell Membrane

    -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


    Arrangement of cell surface proteins


    Cell Membrane Structure


    Lets build a cell membrane together

    • http://www.wisc-online.com/objects/index_tj.asp?objid=AP1101


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