The Plasma Membrane and Cellular Transport

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The Plasma Membraneand Cellular Transport
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Maintaining a Balance

• Maintain HOMEOSTASIS internal balance
• Selective permeability allows some materials to
  pass through membrane while rejecting others.

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Fluid-Mosaic Model

• This description is of a plasma membrane that is
  made up of molecules that are free to flow among
  one another.
• The kinds and arrangements of proteins and lipids
  vary from one membrane to another and give each
  type of membrane specific permeability properties.

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Structure of the Plasma Membrane

• Two-layered structure
• Lipid bilayer
• Made of lipid molecules with protein molecules in
  the lipid layer.
• PROTEINS aid in the movement of materials through
  the membrane.

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Structure of the Plasma Membrane

• The Lipids have two fatty acids attached to
  glycerol and a phosphate group (phospholipid).
• The Polar head of a Phospholipid molecule
  contains a polar phosphorus group, and two
  tails are long, nonpolar carbon chains.

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Structure of the Plasma Membrane
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Structure of the Plasma Membrane

• F Phospholipid bilayer
• Phospholipid
• D Hydrophilic head
• E Hydrophobic tails
• I Cholesterol
• Proteins
• J transport
• G Cytoskeletal filaments
• A Carbohydrate chain
• C Carbohydrate
• Glycolipid
• Glycoprotein

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Proteins of the Plasma Membrane

• 1) Transport Proteins
• 2) Receptor Proteins

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1) Transport Proteins

• Channel Proteins channel for lipid insoluble
  molecules and ions to pass freely through
• Carrier Proteins bind to a substance and carry
  it across membrane, change shape in process

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2) Receptor Proteins

• Bind to chemical messengers (Ex. hormones)
  which sends a message into the cell causing
  cellular reaction

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How do materials move into and out of the cell?

• Materials must move in and out of the cell
  through the plasma membrane.
• Some materials move between the phospholipids.
• Some materials move through the proteins.

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Plasma Membrane Transport

• Molecules move across the plasma membrane by

Active Transport
Passive Transport
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What are three types of passive transport?
Passive Transport

1. Diffusion
2. Facilitated Diffusion
3. Osmosis

ATP energy is not needed to move the molecules
through.
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Passive Transport 1 Diffusion
DIFFUSION

• Also called Brownian Motion random motion of
  molecules.
• Molecules can move directly through the
  phospholipids of the plasma membrane

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What is Diffusion?

• Diffusion is the net movement of molecules from a
  high concentration to a low concentration until
  equally distributed.
• Diffusion rate is related to temperature,
  pressure, state of matter, size of concentration
  gradient, and surface area of membrane.

• Dynamic Equilibrium
• a continuous movement
• of molecules, but no
• change in concentration.

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Concentration Gradient

• The difference in concentration of a substance
  across a space.

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Passive Transport 2 Facilitated Diffusion

• Molecules can move through the plasma membrane
  with the aid of transport proteins
• This is called

FACILITATED DIFFUSION
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What is Facilitated Diffusion?

• Facilitated diffusion is the net movement of
  molecules from a high concentration to a low
  concentration with the aid of channel or carrier
  proteins.

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Passive Transport 3 Osmosis

• Water Molecules can move directly through the
  phospholipids of the plasma membrane
• This is called

OSMOSIS
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What is Osmosis?

• Osmosis diffusion of WATER molecules through a
  membrane from an area of higher water
  concentration to lower water concentration.

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Osmosis in action

• What will happen in the U-tube if water freely
  moves through the membrane but glucose can not
  pass?
• Water moves from side with high concentration of
  water to side with lower concentration of water.
  Movement stops when osmotic pressure equals
  hydrostatic pressure.

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Osmosis and Tonicity

• Tonicity refers to the total solute concentration
  of the solution outside the cell.
• What are the three types of tonicity?
• Isotonic
• Hypotonic
• Hypertonic

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Isotonic

• Solution in which the concentration of water
  (solvent) outside the cell is the same as the
  concentration inside the cell.
• What will happen to a cell placed in an Isotonic
  solution?
• The cell will have no net movement of water and
  will stay the same size.
• Ex. Blood plasma has high concentration of
  albumin molecules to make it isotonic to tissues.

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Hypotonic (Less Concentration)

• Solution in where concentration of water
  (solvent) outside the cell is higher than the
  concentration inside the cell.
• What will happen to a cell placed in a Hypotonic
  solution?
• The cell will gain water and swell.
• If the cell bursts, then we call this lysis. (Red
  blood cells hemolysis)
• In plant cells with rigid cell walls, this
  creates turgor pressure.

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Hypertonic (More Concentrated)

• Solution in which concentration of water
  (solvent) outside the cell is lower than the
  concentration inside the cell.
• What will happen to a cell placed in a Hypertonic
  solution?
• The cell will lose water and shrink.
• In plant cells, the central vacuole will shrink
  and the plasma membrane will pull away from the
  cell wall causing the cytoplasm to shrink called
  plasmolysis.

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Review Tonicity

• What will happen to a red blood cell in a
  hypertonic solution?
• What will happen to a red blood cell in an
  isotonic solution?
• What will happen to a red blood cell in a
  hypotonic solution?

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What are three types of Active transport?

• 1) Active Transport
• 2) Exocytosis
• 3) Endocytosis
• Phagocytosis
• Pinocytosis

Active Transport
ATP energy is required to move the molecules
through.
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Active Transport

• Molecules move from areas of low concentration to
  areas of high concentration with the aid of ATP
  energy.

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The Importance of Active Transport

• Bring in essential molecules
• Rid cell of unwanted molecules (Ex. sodium from
  urine in kidneys)
• Maintain internal conditions different from the
  environment
• Regulate the volume of cells by controlling
  osmotic potential
• Control cellular pH
• Re-establish concentration gradients to run
  facilitated diffusion. (Ex. Sodium-Potassium
  pump and Proton pumps)

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Active Transport 2 Exocytosis (Exo out)

• Movement of large molecules bound in vesicles out
  of the cell with the aid of ATP energy. Vesicle
  fuses with the plasma membrane to eject
  macromolecules.
• Ex. Proteins, polysaccharides, polynucleotides,
  whole cells, hormones, mucus, neurotransmitters,
  waste

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Active Transport 3 Endocytosis (Endo In)

• Movement of large molecules into the cell by
  engulfing them in vesicles, using ATP energy.
• Two types of Endocytosis
• Phagocytosis
• Pinocytosis