Movement through the Cell Membrane

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Movement through the Cell Membrane
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• I. Cell Membrane
• -Regulates what enters and leaves the cell and
  also provides protection and support
• -Lipid Bi-Layer

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-Proteins-run through the bi-layer- the can
function as channels and pumps that help move
material across the membrane -Carbohydrate
Chains-Chemical Identification systems
Head is Hydrophilic the tail is Hyrdophobic
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II. Passive Transport

• Note Cell interior and exterior is surrounded by
  liquid
• -Most important function of the Cell Membrane is
  to regulate the movement of molecules
• A. Simple Diffusion
• -In solutions substances tend to move from HIGH
  CONCENTRATIONS to LOW CONCENTRATIONS until it is
  equal (equilibrium)
• -Diffusion causes substances to move across a
  cell membrane but does not require the cell to
  use energy

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Osmosis

• B. Osmosis
• -Osmosis is the DIFFUSION of water through
  selectively permeable membranes
• -Look on page 186 what is the difference between
  permeable and non-permeable
• -Biological membranes are usually Selectively
  Permeable or Semi-Permeable- This means some
  substances can pass through them while other
  substances cant

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• Isotonic Solutions contain the same
  concentration of solute as solution. When a cell
  is placed in an isotonic solution, the water
  diffuses into and out of the cell at the same
  rate.
• Hypotonic Solutions contain a low concentration
  of solute relative to another solution. When a
  cell is placed in a hypotonic solution, the water
  diffuses into the cell, causing the cell to swell
  and possibly explode.
• Hypertonic Solutions contain a high
  concentration of solute relative to another
  solution. When a cell is placed in a hypertonic
  solution, the water diffuses out of the cell,
  causing the cell to shrivel.
• Turn to page 187 in the text book to see the
  effect of Osmotic pressure on animal and plant
  cells
• Draw it

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C. Facilitated Diffusion

• Energy is not required because the molecules are
  moving from high concentration to low
  concentration. (IT IS DIFFUSION)
• Facilitated diffusion involves the use of a
  protein to facilitate the movement of molecules
  across the membrane.  In some cases, molecules
  pass through Protein channels (gated channel).
• As can be seen below, the protein changes shape
  and releases the molecule to the side of the
  membrane that has the lower concentration.

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Facilitated Diffusion
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III. Active Transport

• -During active transport, carrier proteins within
  the cell membrane move ions or molecules against
  a concentration gradient (low concentration to
  high concentration).
• -Movement against a concentration gradient
  requires energy.
• -Active transport is like a water pump it uses
  energy to pump water uphill.
• Ex Na out and K in

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Other Examples Endocytosis, Exocytosis,
Phagocytosis

• A. Endocytosis-The process by which a cell
  engulfs material to bring it into the cell. A
  pocket is formed that contains the material that
  has been engulfed. (large molecules, food, other
  cells)
• Phagocytosis- is when the cytoplasma comes out
  and grabs a large molecule!
• Pinocytosis- small things
• B. Exocytosis moves material to the outside.  A
  vesicle fuses with the plasma membrane and
  discharges its contents outside.  This allows
  cells to secrete molecules.