Cell Transport

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Cell Transport

• Taking a look at the plasma membrane

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The Cell Membrane

• His friends call him the plasma membrane
• He is thin and flexible
• He has two main functions
• Protection protects the cell from the outside
  environment
• Regulation controls what can enter and exit the
  cell
• He is selective allows some things to pass
  through more easily than others
• He is selectively permeable permeate is a fancy
  way to say pass through.

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What is the Fluid-Mosaic Model?

• Whats a mosaic?
• What does it mean to be fluid?
• The cell membrane is NOT a rigid structure with
  immovable components!
• The cell membrane is fluid-like and flexible
• Within the membrane, molecules can move around

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What Is the Cell Membrane Made of?
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The (Phospho-)Lipid Bilayer

• LIPIDS Phospholipids make up the majority of the
  cell membrane
• Hydrophilic heads (polar) are made of phosphates
  (Phospho)
• Hydrophobic tails (nonpolar) made out of fatty
  acids (Lipid)
• To protect the hydroPHOBIC
• tails from water, they form a
• bilayer which keeps the tails
• inside and the water- loving
• heads outside.

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STEROLS

• Cell membranes of eukaryotes contain sterols
  between the tails of phospholipids
• CHOLESTEROL major membrane sterol in animals
• Make the membrane more firm
• Prevent the membrane from freezing at low
  temperatures

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PROTEINS

• Protein molecules - bring materials into cell and
  receive signals from outside cell
• Integral proteins embedded within the bilayer
• receptor proteins detect signals and transmit
  them inside cell
• transport proteins passage ways that allow
  certain substances to pass
• cell markers carbohydrates attached to help
  cells identify or recognize other cells
• Peripheral proteins lie only on one side of
  membrane (enzymes)

YouTube Membrane
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Draw the Cell Membrane!
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Your turn!

• Use your notes and what youve learned so far to
  complete the matching exercise in your notes
• Protein (only) B
• Carbohydrate (only) D
• Lipid Bilayer A
• Phosphate Head F
• Fatty Acid Tail G
• Involved in Cell Recognition D
• Carbohydrate attached to a lipid E
• Helps move large material across the membrane B
• Carbohydrate attached to a protein C
• Outside cell H

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Solutions

• Molecules dissolved in a liquid SOLUTES
• Liquid/fluid dissolving them SOLVENT
• This makes a SOLUTION
• In a salt solution, ______________ is the solute
  and _____________ is the solvent
• In a sugar solution, sugar is the solute and
  water
• is the solvent.
• 
  
• 
  Dots solute
• 
  Space solvent

SALT
WATER
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Concentration and Equilibrium

• Solutions will spread out their dissolved
  molecules until they are equal throughout.
• EQUILIBRIUM molecules are spread equally
• CONCENTRATION of molecules in an area per
  unit volume.
• CONCETRATION GRADIENT the difference in the
  concentration of molecules across a distance

• 
  

?High concentration more solutes per
unit volume Low concentration less
solutes ? per unit volume
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What happens with a barrier?(like a cell
membrane)

• If solutions on either side of the barrier have
  the same concentration, they are at equilibrium.

• At equilibrium, both the solvent and solute move
  back and forth across the barrier there is
  always movement.

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Transport of Materials Across the Cell Barrier

• Materials move across the plasma
• membrane in two ways
• Passive Transport
• movement across the membrane
• without using energy
• Active Transport
• movement across membrane
• that requires energy

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Types of Passive Transport 1. Diffusion -
simulation

• Solutes move across a membrane from areas of high
  concentration (crowded) to low concentration

• Diffusion random particle movements, so does
  not use energy.

Imagine warm air coming through an open window
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Moving down the gradient requires no energy
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Because cell membranes are selectively
permeable.

• .concentration gradients can build up across a
  cell (like a dam in a lake)

Potential Energy
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What affects the rate of diffusion?

• Concentration of the solution
• Temperature of the solution
• Pressure also speeds up particle motion

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Types of Passive Transport 2. Osmosis

• the process by which water molecules diffuse
  across a cell membrane from an area of higher
  concentration to an area of lower concentration
• Water molecules (fast and small) pass through the
  cells selectively permeable membrane
• Solute molecules are too large to pass -- only
  the water diffuses until equilibrium is reached.

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• Three conditions that control the direction of
  osmosis- In each of the following conditions we
  are comparing the solute concentration outside
  the cell to inside the cell.

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HYPOTONICITY

• the concentration of solute molecules outside the
  cell is lower than the concentration in the
  cytosol.
• This will cause water to flow into the cell until
  equilibrium is reached.

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HYPERTONICITY

• the concentration of solute molecules outside the
  cell is higher than the concentration in the
  cytosol.
• This will cause water to flow out of the cell
  until equilibrium
• is reached.

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ISOTONICITY

• the concentration of solutes outside the and
  inside the cell are equal so water will flow in
  and out of the cell at equal rates.

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How cells deal with osmosis

• Many cells, especially unicellular fresh water
  organisms, must deal with living in extreme
  hypotonic environments.
• -water continually rushes into the cell forcing
  it to constantly rid itself of excess water.
  (Paramecium are unicellular freshwater organisms
  with this problem.)
• contractile vacuoles -organelles that remove
  excess water by collecting it and then
  contracting, pumping the water out of the cell.
  This action requires energy.
• Multi-cellular organisms respond to hypotonic
  environments by pumping solutes out. This helps
  control the flow of water into the cell.

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• Plants in a hypotonic environment can stand
  upright.
• water fills the cell pressing the membrane up
  against the cell wall which is strong enough to
  resist breaking.
• The pressure water molecules exert against the
  cell wall is called turgor pressure.
• In hypertonic environments water leaves the cell
  through osmosis, the cell membrane then shrinks
  away from the cell wall causing the plant to
  wilt. This process is called plasmolysis.

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• Animal cells like red blood cells have no cell
  walls to stop them from expanding and when in a
  hypotonic environment will swell until they
  burst. The bursting of cells is called cytolysis.
• VIDEO

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Types of Passive Transport 3. Facilitated
Diffusion

• Large molecules or those with a charge (not
  soluble in lipids) need the help of a protein to
  pass across a cell membrane
• Proteins form a channel

and molecules move through the doorway. From
high to low concentration. Each channel is
specific to a particular type of
molecule Doesnt require energy gt passive
transport
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Each carrier protein is specific for a certain
molecule

• As soon as the molecule binds to its carrier
  protein, the carrier protein changes shape
• The change in shape shields the molecule from the
  hydrophobic interior of the lipid bi-layer
• The molecule can then be delivered either into or
  out of the cell
• Example- glucose is too large to diffuse across
  the membrane but essential for the cell
• VIDEO -

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Diffusion Through Ion Channels-

• allow for the passage of ions through the cell
  membrane
• Each ion channel is specific for one kind of ion
• Some ion channels are always open
• Some ion channels have gates that open and close
  as needed
• They open and close in response to 3 different
  stimuli
• Stretching of the cell membrane
• Electrical signals
• Chemicals in their environment

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Active Transport

• Movement AGAINST the concentration gradient
  requires energy (because it moves solutes from
  low to high concentrationwhere its already
  crowded)
• Difference in solution concentrations
  concentration gradient
• Three types of active
  transport

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Active Transport1. Pump

• Pump a protein PUSHES molecules across the
  membrane

Ex the Sodium and Potassium (Na/K) Pump.
YouTube Na/K Pump
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Active Transport2. Endocytosis

• Endocytosis (endoin) a pocket (vacuole) forms
  around a large molecule outside the cell and buds
  inward to release the material inside the cell.

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Active Transport3. Exocytosis

• Exocytosis (exoout) a vacuole inside the cell
  fuses with the cell membrane and forces the
  material outside the cell.

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Animation