Cell Membranes and Transport

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Cell Membranes and Transport
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What is going on in this picture?
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Phospholipids
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Phospholipids

• Fatty acid chains
• A phosphate group
• Glycerol backbone.
• Polar heads
• Nonpolar fatty acids

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The Fluid Mosaic Model
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Fluid Mosaic Model

• Transports
• Small molecules
• Between the phospholipids
• Large molecules?!

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Composition of the Plasma Membrane

• Lipid bilayer
• Peripheral proteins
• Integral proteins
• Cholesterol
• Glycoproteins
• Alpha helix protein

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Homeostasis

• Maintaining a Balance
• Nutrients
• Water
• Wastes
• Selectively permeable

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Diffusion
Cell membrane
Outside cell
Inside cell
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Diffusion
Cell membrane
diffusion
Outside cell
Inside cell
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Diffusion
Cell membrane
Outside cell
Inside cell
EQUILIBRIUM
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Facilitated Diffusion
Cell membrane
diffusion
Protein channel
Outside cell
Inside cell
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Facilitated Diffusion
Cell membrane
diffusion
Protein channel
Outside cell
Inside cell
EQUILIBRIUM
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Osmosis
CONCENTRATED SOLUTION
DILUTE SOLUTION
Cell membrane partially permeable.
Sugar molecule
VERY Low conc. of water molecules. High water
potential.
VERY High conc. of water molecules. High water
potential.
Outside cell
Inside cell
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Osmosis
Cell membrane partially permeable.
Low conc. of water molecules. High water
potential.
OSMOSIS
High conc. of water molecules. High water
potential.
Outside cell
Inside cell
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Osmosis
Cell membrane partially permeable.
OSMOSIS
Outside cell
Inside cell
EQUILIBRIUM. Equal water concentration on each
side. Equal water potential has been reached.
There is no net movement of water
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Cellular Transport - Passive

• No energy is needed to move particles
• Types of passive transport
• Diffusion
• Facilitated diffusion
• Osmosis

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What determines the rate of diffusion?

• Steepness of the concentration gradient
• Temperature
• Surface area
• Type of molecule or ion diffusing

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Whats the Point?
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Cell Concentrations

• Hypertonic solutions
• More dissolved solute, less water
• Hypotonic solutions
• Less dissolved solute, more water
• Isotonic solutions
• Equal amounts of dissolved solute and water

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Cell Concentrations Isotonic

• If the outside solution is isotonic to the inside
  of the cell
• The inside of the cell has the same amount of
  dissolved solute as outside the cell
• So the water moves
• IN and OUT at equal rates!

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Cell Concentrations Hypotonic

• If the outside solution is hypotonic to the
  inside of the cell
• The outside of the cell has less solute and more
  water than the inside of the cell
• So the water moves
• INTO the cell until equilibrium is reached.

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Cell Concentrations Hypertonic

• If the outside solution is hypertonic to the
  inside of the cell
• The outside of the cell has more solute and less
  water than the inside of the cell
• So the water moves
• OUT of the cell until equilibrium is reached.

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Overcoming Osmosis

• Contractile vacuoles
• Turgor pressure

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Cellular Transport - Active

• Active transport
• Energy is needed to move particles UP the
  concentration gradient

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Cellular Transport - Active

• Carrier proteins
• Endocytosis
• Pinocytosis
• Phagocytosis
• Exocytosis

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How Molecules Cross the Membrane