Cellular Transport Methods

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Cellular Transport Methods

• Chapter 4

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Two Categories

• Passive transport does not require cellular
  energy. Instead the energy involved comes from
  the kinetic energy of the molecules.
• Active transport cellular energy, usually in the
  form of ATP, to power these processes.  

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Diffusion

• Movement of like molecules down a concentration
  gradient (movement from high to low
  concentration)
• Occurs in liquids, solids or gasses
• Passive

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A drop of dye inters a bowl of water. Gradually,
the dye molecules become evenly dispersed through
the molecules of water.
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Facilitated Diffusion

• Passive
• Solutes diffuse through a channel in the interior
  of a transport protein
• Net movement is down the concentration gradient
  (from high to low)

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Transport Proteins

• Span the lipid bilayer
• Interior is able to open to both sides
• Change shape when they interact with solute
• Move polar molecules and ions across cell
  membrane lipid bilayer

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Facilitated Diffusion of Glucose
glucose transporter
solute (glucose)
high
low
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Factors Affecting Diffusion Rate

• Concentration gradient
• Steeper gradient, faster diffusion
• Molecular size
• Smaller molecules, faster diffusion
• Temperature
• Higher temperature, faster diffusion
• Electrical or pressure gradients
• Greater gradient, faster diffusion

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Active Transport

• Uses energy in the form of ATP
• Solutes diffuse through a channel in the interior
  of a transport protein
• Moves solute against a concentration gradient
  (from low to high)
• Protein involved is called a pump
• Example of active transport in the calcium pump

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Endocytosis and Exocytosis

• Active transport
• Bulk flow mechanisms of transport
• Enable the cell to take in very large packages of
  molecules...say a food item from the environment.
  

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Endocytosis

• Moves large substances into a cell
• Three types
• Receptor-mediated
• Phagocytosis
• Pinocytosis

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Receptor Mediated-Endocytosis

• Receptors on the membrane bind to substances such
  as hormones, vitamins or minerals
• A pit forms beneath the receptor
• Pit sinks and closes on itself forming a vesicle
• The vesicle moves into the cell, later releasing
  its contents to the cell interior

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Phagocytosis or Cell EatingPinocytosis or Cell
Drinking

• Involves receptors
• Microfilaments change cell shape to form a
  bulging lobe of cell membrane that surrounds a
  target and forms a vesicle
• The vesicle moves to the interior of the cell,
  later releasing its contents

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Phagocytosis of an Edible Bacterium by an Amoeba
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Exocytosis

• A cytoplasmic vesicle fuses with the cell
  membrane and its contents are released outside
  the cell

Cell membrane
cytoplasm
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Osmosis

• Osmosis is the net movement of water between two
  regions separated by a selectively permeable
  membrane.
• Movement of water is from high concentration to
  low concentration

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Solute concentrations effect osmosis The
membrane side with the most solute particles has
the lower water concentration.
semipermeable membrane between two compartments
protein molecule
water molecule
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Osmotic Pressure

• Living cells cant increase in volume
  indefinitely.
• Fluid pressure building up inside the cell
  eventually counters waters movement inward.
• Osmotic pressure is the pressure at which the net
  movement of water in a cell is zero.