Cellular Transport Notes

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Cellular Transport Notes

• Ch. 7.4

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About Cell Membranes

• All cells have a cell membrane
• Functions
• Controls what enters and exits the cell to
  maintain an internal balance called homeostasis
• Provides protection and support for the cell

TEM picture of a real cell membrane.
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About Cell Membranes (continued)

• Structure of cell membrane
• Phosphlipid Bilayer -2 layers of phospholipids
• Phosphate head is polar (water loving)
• Fatty acid tails non-polar (water fearing)
• Proteins embedded in membrane

Phospholipid
Lipid Bilayer
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Fluid Mosaic Model of the cell membrane
Polar heads love water dissolve.
Membrane movement animation
Non-polar tails hide from water.
Carbohydrate cell markers
Proteins
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About Cell Membranes (continued)

• 4. Cell membranes have pores (holes) in it
• Selectively permeable Allows some molecules in
  and keeps other molecules out
• The structure helps it be selective!

Pores
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Structure of the Cell Membrane
Outside of cell
Carbohydrate chains
Proteins
Lipid Bilayer
Transport Protein
Phospholipids
Inside of cell (cytoplasm)
Animations of membrane structure
Go to Section
7
Cells

• Have to maintain a constant internal environment
  (or homeostasis)
• respond to the concentration gradient of the
  environment by moving molecules across membranes
  to either balance inside and outside
  concentrations (i.e. equilibrium) or to stockpile
  more

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Transport begins with tonicity

• Tonicity is the concentration of dissolved
  solutes inside compared to outside the cell
• Determine the concentration of solutes found
  inside the cell
• Determine the concentration of solutes found
  outside the cell
• Compare the two where is the concentration
  greater?
• Molecules move from high to low!

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Isotonic

• Concentration of dissolved solutes is equal to
  cell contents

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Hypertonic

• Hyper there is a higher solute concentration
  outside the cell

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Hypotonic

• Hypo there is a low solute concentration
  outside the cell

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• So once we know the concentration gradient we can
  start thinking about how cells move molecules in
  and out of the cells

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Types of Cellular Transport

• Animations of Active Transport Passive Transport

• Passive Transport
• cell doesnt use energy
• Diffusion
• Facilitated Diffusion
• Osmosis
• Active Transport
• cell does use energy
• Protein Pumps
• Endocytosis
• Exocytosis

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• Passive transport

• Active transport

• No energy required
• Movement from high to low area of concentration
• Molecules move with concentration gradient
• Diffusion
• Osmosis
• Facilitated diffusion

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Passive Transport 1. Diffusion
Simple Diffusion Animation

• Diffusion random movement of particles from an
  area of high concentration to an area of low
  concentration.
• (High to Low)
• Diffusion continues until all molecules are
  evenly spaced (equilibrium is reached)-Note
  molecules will still move around but stay spread
  out.

http//bio.winona.edu/berg/Free.htm
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Types of Passive Transport (high to low)

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

Click here for diffusion animated explanation
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Passive Transport 2. Facilitated Diffusion
A
B

• 2. Facilitated diffusion diffusion of specific
  particles through transport proteins found in the
  membrane
• Transport Proteins are specific they select
  only certain molecules to cross the membrane
• Transports larger or charged molecules

Facilitated diffusion (Channel Protein)
Diffusion (Lipid Bilayer)
Carrier Protein

• http//bio.winona.edu/berg/Free.htm

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Types of Passive Transport (high to low)

• Facilitated diffusion
• Diffusion of bigger molecules (but still smaller
  than particles) through channel proteins

Click here for facilitated diffusion explanation
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Passive Transport 2. Facilitated Diffusion
Glucose molecules
Cellular Transport From a-
High
High Concentration

• Channel Proteins animations

Cell Membrane
Protein channel
Low Concentration
Low
Transport Protein
Through a ?
Go to Section
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Osmosis animation
Passive Transport 3. Osmosis

• 3.Osmosis diffusion of water through a
  selectively permeable membrane
• Water moves from high to low concentrations

• Water moves freely through pores.
• Solute (green) to large to move across.

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• Passive transport

• Active transport

• No energy required
• Movement from high to low area of concentration
• Molecules move with concentration gradient
• Diffusion
• Osmosis
• Facilitated diffusion

• Requires energy
• Movement from low to high area of concentration
• Molecules move against concentration gradient
• Sodium-potassium ion pump
• Endocytosis
• Exocytosis

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Types of Active Transport
Sodium Potassium Pumps (Active Transport using
proteins)

• 1. Protein Pumps -transport proteins that require
  energy to do work
• Example Sodium / Potassium Pumps are important
  in nerve responses.

Protein changes shape to move molecules this
requires energy!
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Types of Active Transport (low to high)

• Ion pump
• Ions are stockpiled in an already highly
  concentrated area

Click here for Sodium-potassium pump animation
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Types of Active Transport

• 2. Endocytosis taking bulky material into a
  cell
• Uses energy
• Cell membrane in-folds around food particle
• cell eating
• Think pac-man
• This is how white blood cells eat bacteria!

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Types of Active Transport

• 3. Exocytosis Forces material out of cell in
  bulk
• cell pooping
• membrane surrounding the material fuses with cell
  membrane
• Cell changes shape requires energy

Endocytosis Exocytosis animations
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Endocytosis (in) Exocytosis (out)
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Summary
Passive Transport Both Active Transport
No energy required Movement with the gradient Diffusion, osmosis, facilitated diffusion Maintains equilibrium Movement through channel proteins Movement of small ions molecules Maintains homeostasis Requires ATP Movement against gradient Ion pump or endo/exocytosis Movement of large particles Stockpiles materials (extras)
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Now well focus on water movement because it
moves more freely than other molecules
Notice the sugar molecules are too big to pass
through the membrane but water is not
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Effects of Osmosis on Life

• Osmosis- diffusion of water through a selectively
  permeable membrane
• Water is so small and there is so much of it the
  cell cant control its movement through the cell
  membrane
• Next lets see how different conditions
  (iso/hypo/hyper) can affect a cell by osmosis

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Hypotonic Solution

• Osmosis Animations for isotonic, hypertonic, and
  hypotonic solutions

Hypotonic The solution has a lower
concentration of solutes and a higher
concentration of water than inside the cell. (Low
solute High water)
Result Water moves from the solution to inside
the cell) Cell Swells and bursts open
(cytolysis)!
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Hypotonic solution

• Water moves inside of cell, toward higher solute
  concentration
• Cell size increases

Note the cell is hypertonic compared to the
solution around it
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How will you remember? Think hypo-hippo

• A cell in a hypo- environment will swell like a
  big fat hippo!

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Hypertonic Solution

• Osmosis Animations for isotonic, hypertonic, and
  hypotonic solutions

Hypertonic The solution has a higher
concentration of solutes and a lower
concentration of water than inside the cell.
(High solute Low water)
shrinks
Result Water moves from inside the cell into
the solution Cell shrinks (Plasmolysis)!
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Hypertonic solution

• Water moves outside of the cell, toward higher
  solute concentration
• Cell size shrinks

Note the cell is hypotonic compared to the
solution around it
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Isotonic Solution

• Osmosis Animations for isotonic, hypertonic, and
  hypotonic solutions

Isotonic The concentration of solutes in the
solution is equal to the concentration of solutes
inside the cell.
Result Water moves equally in both directions
and the cell remains same size! (Dynamic
Equilibrium)
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Isotonic solution

• Water moves equally in BOTH directions
• Therefore, cell size does not change

Note the cell is also isotonic compared to the
solution around it
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What type of solution are these cells in?
C
B
A
Hypertonic
Isotonic
Hypotonic
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Review

• Hypotonic
• Lower solute concentration outside the cell
• Water moves in
• Cell size increases
• E.g. Diluted solution

• Isotonic
• Same solute concentration
• Water moves in and out
• No change in cell size

• Hypertonic
• Higher solute concentration outside the cell
• Water moves out
• Cell size decreases
• E.g. Strong salt solution