Cellular Transport

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Cellular Transport

• How molecules move in and out of cells

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Phospholipid bilayer

• Hydrolipid Heads
• Next to extracelluar fluid and cytoplasm
• likes water
• Hydrophobic tails
• Inside bilayer
• dislikes water
• Phospholipds not bonded to one another, therefore
  the double layer is fluid (moveable)
• To help cells change shape

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Transport proteins

• Embedded within phospholipid bilayer
• Regulate the movement of WATER SOLUBLE molecules
  (which cannot pass directly across the bilayer)
• Outer shell made of HYDROPHOBIC amino acids
• Inner channel made of HYDROPHILIC amino acids

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Movement of Molecules

• Depend on 2 factors
• Concentration of molecules
• molecules / volume
• Gradient across the membrane
• Difference in concentration between 2 regions
• Moclecules tend to move from
• HIGH concentration ? LOW concentration
  areas
• Eg. Concentration gradient, pressure gradient,
  electrical gradient

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Outside the cell Inside the cell
Which direction will the molecules be moving
according to the gradient?

• Answer
• Molecules will move INTO the cell because
• more molecules outside the cell, therefore a HIG
  gradient
• less molecules inside the cell, therefore a LOW
  gradient

Plasma membrane
REMEMBER! Moclecules tend to move from
HIGH concentration ? LOW concentration areas
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Cellular Transport - Overview

• Passive Transport
• Simple diffusion
• Facilitated diffusion
• Osmosis (passive water transport)
• Active Transport
• Active transport
• Endocytosis
• Pinocytosis, Phagocytosis, Receptor-Mediated
  Endocytosis
• Exocytosis

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1. Passive Transport

• Due to a gradient (difference in concentration
  between 2 regions)
• Requires NO energy from the cell
• Gradient provides potential energy that causes
  the movement of molecules
• Plasma membrane is semi-permeable (allow some
  molecules to pass through)
• Direction of movement HIGH concentration ? LOW
  concentration areas

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1a. Simple Diffusion

• Diffusion of gases, water, lipid soluble
  (Hydrophobic) molecules through the bilipid layer
• Speed of diffusion depends on
• Gradient
• Size of molecules
• Diffusion continues until the concentration of
  molecules in both regions are equal (Equilibrium)

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(No Transcript)
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1b. Facilitated Diffusion

• Molecules diffuse through protein channels in a
  Transport Protein
• Molecules bind to Transport protein, it changes
  shape and transport molecule across the membrane
• Transport proteins are reuseable, and remain in
  the bilayer

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1b. Facilitated Diffusion

• Diffusion of
• charged ions (K, Na, Ca2)
• Amino acids (because they are too big)
• Monosaccharides (simple sugars)
• Direction of movement HIGH concentration ? LOW
  concentration areas
• Rate of diffusion depends on
• Number of Transport proteins present
• Gradient present
• Slower than Simple diffusion

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1c. Osmosis diffusion of H2O

• Diffusion of WATER across membranes
• Water diffuses from area of HIGH concentration ?
  LOW concentration
• osmosis stops when the system has reached
  EQUILIBRIUM

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2a. Active Transport

• Moving materials UP the gradient
• Direction of movement LOW concentration ? HIGH
  concentration areas
• Requires energy from the cell in the form of ATP
  (adenosinbe triphosphate)
• Requires Transport proteins with 2 active sites,
  one for the molecule and one for ATP

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ATP
3 Phospate groups

• Adenosine triphosphate
• An energy carriermolecule
• When ATP loses a phosphate group it gives off
  energy to become

• ADP (adenosine diphosphate)
• ATP ? ADP Phosphate (Pi)

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Transport proteins for Active Transport
Transport Protein

• ATP binding site always inside the cell because
  the cell must provide energy for transport
• Molecule binding site may be inside or outside
  the cell
• Transport protein changes shape after binding ATP
  to transport molecules from LOW concentration ?
  HIGH concentration areas

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2b. Endocytosis

• 3 different ways cells can actively gather
  materials (ie. Nutrients and fluids)
• Pinocytosis (cell drinking)
• Phagocytosis (cell eating)
• Receptor Mediated Endocytosis

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2a. Pinocytosis (cell drinking)

• To transport fluid from outside the cell
• Small dimple form in plasma membrane (2 in
  diagram)
• Surrounding fluid contained within a tiny
  vessicle (4 in diagram) to be used by the cell
• Eg. Cells in your intestine

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2a. Phagocytosis

• process in which cells take in large particles,
  clumps of food and even other cells!
• extensions of cytoplasm surround and engulf the
  object
• Ameba (asingle celled organism) uses this process
  to capture food

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2a. Receptor-mediated endocytosis

• A way for cells to gather specific materials
• molecules in the extracellular fluid bind to
  receptors (Clatherin) on the cell surface
• Clatherins are usually found in concentrated
  areas called a Coated Pit
• Coated Vesicle (because it is coated with
  clatherin INSIDE) is pinched off the plasma
  membrane

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3c. Exocytosis

• A way for cells to eliminate waste
• Reverse of endocytosis
• Vesicle moves to cell surface, fuses with plasma
  membran and contents diffuse away from the cell

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Some real life pictures!
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What is this?
Receptor mediated endocytosis see the coated pit!
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What is this?
Phagocytosis the white blood cell is engulfing
2 bacteria cells
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Cellular Transport - Summary

• Passive Transport
• no energy required
• from High ? Low concentration
• Simple diffusion
• gases, water, lipid soluble (Hydrophobic)
  molecules through the bilipid layer
• Faciltated diffusion
• Molecules bind to Transport protein, it changes
  shape and transport molecule across the membrane
• Osmosis (passive water transport)
• Diffusion of WATER across membranes

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Cellular Transport - Summary

• Active Transport
• from Low ? High concentration
• Active transport
• requires ATP
• Transport protein has 2 binding sites
• Endocytosis
• A method for cells to gather non-specific or
  specific materials from extracellular fluid
• Pinocytosis, Phagocytosis, Receptor-Mediated
  Endocytosis
• Exocytosis
• Cells dispose of waste