The Cell Membrane

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The Cell Membrane

• Also known as a
• plasma membrane

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How does the cell membrane help regulate
homeostasis?
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Made of phospholipids with embedded proteins.

• Phospholipid
• ?

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• Cholesterol strengthens the cell membrane
• Proteins help materials cross the membrane, part
  of the cytoskeleton
• Carbohydrates help identify cell types

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• Cell-surface marker identifies cell type
  and identifies cells as self.

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Intracellular receptor

• http//highered.mcgraw-hill.com/olc/dl/120069/bio0
  6.swf

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• Membrane receptor recognizes and binds to
  substances outside the cell

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Membrane receptors

• http//highered.mcgraw-hill.com/sites/0072495855/s
  tudent_view0/chapter2/animation__receptors_linked_
  to_a_channel_protein.html

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• Transport protein Helps substances move
  across cell membrane.

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• Cellular Transport
• Sections 3-4 and 3-5

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I. Passive Transport

• Materials move across membranes because of a
  concentration gradient.
• Does not require energy.

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A. Diffusion
Diffusion is a type of passive transport.

• Molecules move from an area of high concentration
  to an area of low concentration.

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• Continues until equilibrium is reached

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B. Osmosis

• How is osmosis different from diffusion?
• It only deals with movement of water

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Three Types of Solutions

• Isotonic same concentration of dissolved
  particles inside and outside of cell cell stays
  the same size

• Hypertonic more dissolved particles outside
  cell than in cell cell loses water and shrinks

• Hypotonic less dissolved particles outside cell
  than in
• cell cell gains water and swells

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• Osmosis in Plant cells
• Hypertonic solutions result in plasmolysis
• (plasma membrane pulls away from cell wall)

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• Practice Problem
• Sea water has a higher concentration of salt than
  human body cells have.
• Why might drinking large amounts of sea water be
  dangerous for humans?

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C. Facilitated Diffusion

• Facilitated diffusion is passive transport of
  materials across the plasma membrane with the aid
  of transport proteins .
• Molecules such as sugars or amino acids enter
  the cell through facilitated diffusion
• Channel protein shown at right provides a
  tubelike opening for small molecules

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• Carrier proteins change shape to let larger
  molecules into the cell

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II. Active Transport
Cells use energy to transport materials against
the concentration gradient
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Active Transport

• Active transport is powered by chemical energy
  (ATP).

• Active transport occurs through transport proteins

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Endocytosis
A cell can import large materials in vessicles
during the process of endocytosis.

• Cells use energy to transport material in
  vessicles.

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Exocytosis

• Exocytosis is the process of expelling material
  from the cell.

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Sodium-potassium pump

• http//highered.mcgraw-hill.com/sites/0072495855/s
  tudent_view0/chapter2/animation__how_the_sodium_po
  tassium_pump_works.html

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