CH. 6 : How Things

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CH. 6 How Things Get Into and Out of Cells
Elaine Nguyen, P.2
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Cell Membrane
Protein is embedded in membrane- can not flip-flop

• Regulates passage of materials into out of cell
  (selectively permeable)
• Allows for specialized chemical environments

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Water Potential

• Water potential- H2O moves from region of greater
  to those of lower water concentration
• Depends on pressure concentration

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Water Potential

• Water potential pressure potential solute
  potential
• Water always moves from high water potential
  (higher free energy, more water molecules) to an
  area of lower water potential ( lower free
  energy, less water molecules)

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Osmotic Potential

• Is opposite of water potential
• High osmotic potential (solute potential) low
  water potential

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Bulk Flow

• Bulk flow- molecules altogether in same
  direction, cell to cell
• Example
• Air moving in lungs
• Blood moving through veins
• Water flowing down a stream

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Diffusion

• Diffusion- moves molecules/ions independently
  randomly until evenly distributed, net random
  movement of molecules
• Only efficient over short distance
• More effective with small molecules
• Moves down a concentration gradient
• Does not require energy

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Diffusion

• CO2, O2 are non-polar, move easily across membrane

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Diffusion and Dynamic Equilibrium

• All gradients have ceased to exist
• Random motion continues but net movement is zero
• As many solute molecules move from right to left
  as left to right
• As many solvent molecules move from right to left
  as left to right

http//resources.yesican.yorku.ca/trek/scisat/fina
l/grade9/trans_chlorine1.html
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Diffusion and Countercurrent Exchange
http//sps.k12.ar.us/massengale/bird_notes_bi.htm
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Diffusion and Countercurrent Exchange

• Very good site to see diagrams of countercurrent
  exchange

More efficient is countercurrent exchange, in
which the respiratory medium and the blood move
in opposite directions. The gas gradient is
maintained across the whole surface.
http//sps.k12.ar.us/massengale/bird_notes_bi.htm
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Osmosis
Most common molecule in cell is H2O
Solutions start off Isotonic- equal concentrations
Hypertonic vs. Hypotonic

• Osmosis- movement of H2O molecules across a
  membrane
• Osmotic pressure- pressure required to stop
  osmotic movement, measures osmotic potential

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Effects of osmosis
http//www.emc.maricopa.edu/faculty/farabee/BIOBK/
BioBookDiversity_3.html
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Effects of osmosis
This protista is in salt water. What are the
effects of salt water on is?
http//www.microbeworld.org/htm/aboutmicro/microbe
s/types/protista.htm
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Large organism and osmosis

• How does the shark deal with being in a
  hypertonic solution (salt water)

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Turgor Pressure

• Plants hypertonic to their environment (H2O tends
  to diffuse into cells)
• Turgor- internal pressure on cell wall that keeps
  cell walls stiff the plant body crisp
• Direct results of osmosis

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Carrier-Assisted Transport
(watch what the antiport does transports!)

• Necessary for those molecules with polar
  functional groups (cause them to be hydrophilic
  cannot move freely)
• Transport proteins highly selective
• Ex facilitated diffusion, active transport

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• Transports ions, hydrophilic molecules
• Rate depends on steepness of concentration
  gradient

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• Unlike facilitated diffusion, active transport
  moves against a concentration gradient requires
  energy

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Sodium- Potassium Pump

• 1/3 of energy in a resting animal is used in this
  pump
• Na pumped out
• K pumped in
• Ions move up a concentration gradient
• Transport protein changes shape as it works

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More Active transportglucose into liver
http//mcb.berkeley.edu/courses/mcb136/topic/Endoc
rine_Autonomic/SlideSet2/endo2_files/endshow.htm
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phosphate group
An example of active transport
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Types of Transport Molecules
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Exocytosis
Usually vesicles destined for exocytosis have
budded off from Golgi Apparatus

• Exocytosis- when vesicle reaches the cell
  surface, its membrane fuses with the membrane of
  the cell it can expel its contents outside

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Endocytosis

• Phagocytosis
• Pinocytosis
• Receptor-mediated endocytosis

• Endocytosis- materials to be taken into the cell
  causes the membrane to bulge inward, making a
  vesicle enclosing the substance

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Example of Pinocytosis

• Ovum ( egg ) drinks fluid released by nurse cells

http//www.hwscience.com/Bio/HAP/HAP.html
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Receptor Mediated Endocytosis

• LDLs in the form of cholesterol are brought into
  the cell.
• Clatherin is a peripheral membrane protein- this
  is where LDLs are brought in

http//cellbio.utmb.edu/cellbio/recend2.htmLDL20
receptors
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http//cellbio.utmb.edu/cellbio/recend2.htmLDL20
receptors
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Communication Between Cells

• Most communication done by chemical agents that
  pass through the cell membrane or interact with
  surface receptors

• Plasmodesmata- allows for direct communication
  (in plant tissues) or gap junctions (in animal
  tissues) allowing for material and electrical
  impulses to pass

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http//fulton.edzone.net/cites/winkler-science/tea
m1/chap1.html