Review of Actin and Myosin

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Review of Actin and Myosin

• http//www.blackwellpublishing.com/matthews/myosin
  .html
• http//www.andrew.cmu.edu/user/berget/Education/Te
  chTeach/muscle/2DMACycle.html
• http//www.andrew.cmu.edu/user/berget/Education/Te
  chTeach/muscle/3DMACycle.html
• http//www.studiodaily.com/main/technique/tproject
  s/6850.html

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Cytoplasmic Streaming

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Membrane Structure and Function

• Membranes are of utmost importance to the cell as
  a whole, and to many of the organelles contained
  in the cell, because they act as selective
  barriers to let in only the substances that each
  cell or specific organelle needs to function
  properly.

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Fluid Mosaic Model

• Membranes are primarily made up of phospholipids
  and proteins held together by weak interactions
  that cause the membrane to be fluid.
• There are both integral and peripheral proteins
  embedded in the fluid membrane.

http//www.emc.maricopa.edu/faculty/farabee/BIOBK/
BioBookTOC.html
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Fluid Mosaic Model

• Integral proteins
• those that are completely embedded in the
  membrane, some of which are transmembrane
  proteins
• Peripheral proteins
• loosely bound to the membranes surface

http//www.emc.maricopa.edu/faculty/farabee/BIOBK/
BioBookTOC.html
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Fluid Mosaic Model

• Carbohydrates on the membrane are crucial in
  cell-to-cell recognition (important in immunity)
  and in developing organisms (for tissue
  differentiation)
• Many are oligosaccharides and vary from species
  to species one reason why blood transfusions
  must be type-specific.

http//www.emc.maricopa.edu/faculty/farabee/BIOBK/
BioBookTOC.html
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Fluid Mosaic Model
The membrane is selectively permeable A
membrane that allows only certain materials to
cross it Amphipathic is both hydrophilic and
hydrophobic
http//sun.menloschool.org/cweaver/cells/c/cell_m
embrane/fluid_mosaic.jpg
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Passive Transport Across the Membrane

• Hydrocarbons, carbon dioxide, and oxygen are
  hydrophobic substances that can pass easily
  across the membrane by passive diffusion.
• In passive diffusion, a substance will travel
  from high concentration to low concentration.

http//www.emc.maricopa.edu/faculty/farabee/BIOBK/
BioBookTOC.html
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Passive Transport Across the Membrane

• When diffusing as such, down a concentration
  gradient, no work is done.
• This movement relies only on the thermal motion
  energy intrinsic to the molecule diffusing.

http//www.emc.maricopa.edu/faculty/farabee/BIOBK/
BioBookTOC.html
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Passive Transport Across the Membrane

• Diffusion Gradient Movement of particles from
  low to high concentration

epswww.unm.edu
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Passive Transport Across the Membrane

• Osmosis is the passive transport of water.
• In osmosis, water flows from a hypotonic solution
  (the solution with lower solute concentration) to
  a hypertonic solution (one with a higher solute
  concentration).

http//www.emc.maricopa.edu/faculty/farabee/BIOBK/
BioBookTOC.html
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Passive Transport Across the Membrane

• HypOtonic

H2O water NaCl solute
NaCl
NaCl
NaCl
NaCl
NaCl
Isotonic
NaCl
HYPERtonic
NaCl
NaCl
Inside 20 solute, 80 water Outside 40 solute,
60 water Water moves High to Low Into the cell
NaCl
NaCl
H2O
NaCl
50 NaCl 50 water Inside and outside Water moves
in and out
NaCl
Inside 30 NaCl, 70 waterOutside 10 NaCl, 90
waterWater moves High to LowOut of cell
http//library.thinkquest.org/C006669/media/Biol/i
mg/solutions.gif
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Passive Transport Across the Membrane

• Healthy plants have a cell wall that restricts
  cell expansion, resulting in pressure on the cell
  wall from within called turgor pressure
  (hypOtonic).
• The pressure of each cell wall against its
  neighbor results in stiffness that allows the
  plant to stay upright. (animal cells explode in
  hypotonic states)
• Plasmolysis (hypertonic) or Plant wilting is a
  result of water lose and lose of turgur pressure

http//www.uic.edu/classes/bios/bios100/lecturesf0
4am/wilt.jpg
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Dialysis Tubing
http//library.thinkquest.org/C006669/media/Biol/i
mg/solutions.gif

• The example above shows how when the inside of
  the cell becomes hypotonic, the outside becomes
  hypertonic, and visa versa.

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Passive Transport Across the Membrane

• Facilitated Diffusion passive transport with the
  help of proteins.
• Hydrophilic substances get across the membrane
  through transport proteins.
• Transport proteins work in two ways, and are
  specific to the substances they transport.

http//cellbio.utmb.edu/cellbio/membrane.htm
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Passive Transport Across the Membrane

• Transport proteins
• 1. provide a hydrophilic channel through which
  a molecule can pass
• 2. can bind loosely to the molecule and carry
  it through the membrane
• This type of passive transport is call
  facilitated diffusion.

http//www.emc.maricopa.edu/faculty/farabee/BIOBK/
BioBookTOC.html
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Active Transport Across the Membrane

• Substances are moved across their concentration
  gradient, from low to high concentration.
• The cell must expend energy.
• Crucial for the cell to maintain sufficient
  quantities of substances that are relatively rare
  in their environment.

http//members.tripod.com/a170y/atp.html
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Active Transport Across the Membrane

• Specific transmembrane proteins are responsible
  and ATP provides the energy by transferring one
  of its phosphates to the transport protein.
• This phosphate transfer causes the protein to
  change its conformation to allow for passage of a
  substance.

http//www.emc.maricopa.edu/faculty/farabee/BIOBK/
BioBookTOC.html
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Active Transport Across the Membrane

• Ions have both a chemical and a voltage gradient
  across the membrane, causing an electrochemical
  gradient.
• The inside of the cell is slightly more negative
  than the outside, so that membrane potential
  favors the movement of cations into the cell.

http//www.emc.maricopa.edu/faculty/farabee/BIOBK/
BioBookTOC.html
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Active Transport Across the Membrane

• The sodium-potassium pump works by exchanging
  three sodium ions for two potassium ions across
  the cell membrane so for each turn of the pump
  there is a net transfer of one positive charge
  from the cell interior to the exterior.

http//www.emc.maricopa.edu/faculty/farabee/BIOBK/
BioBookTOC.html

• This electrogenic (electrochemical)pump generates
  
• voltage across the membrane.

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Active Transport Across the Membrane

• Sodium Potassium Pump Animation

www.uic.edu/.../bios100/lecturesf04am/lect09.htm
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Active Transport Across the Membrane

• In cotransport, an ATP pump that transports a
  specific solute indirectly drives the active
  transport of other substances.
• In this process, the substance initially pumped
  across the membrane will do work, providing
  energy for the transport of another substance
  against its concentration gradient, as it leaks
  back across the membrane with its concentration
  gradient.

http//vlib.org/Science/Cell_Biology/membranes.sht
ml
Animation of Transport
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Active Transport Across the Membrane

• H is actively pumped out by hydrolyzing ATP
• H accumulated outside the membrane, generating a
  concentration and electrochemical gradient
• This is a common means to store energy in cells
• Used in mitochondria chloroplasts
• The H cannot cross the membrane, but there is a
  carrier protein.
• H binds to carrier protein, but sucrose must
  also bind. When both are bound, the configuration
  changes and the protein opens to the membrane
  interior.
• This is known as cotransport as two molecules are
  pumped across a membrane, one "downhill" (with
  its gradient) coupled with one "uphill" (against
  its gradient)
• It is also known as a symport as both molecules
  are crossing in the same direction
• If the molecules are moving in opposite
  directions itis known as an antiport

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Movement of Large Molecules

• Exocytosis
• vesicles from the cells interior fuse with the
  cell membrane expelling their contents to the
  exterior
• Endocytosis
• the cell forms new vesicles from the plasma
  membrane in a kind of reverse exocytosis three
  types

http//www.emc.maricopa.edu/faculty/farabee/BIOBK/
BioBookTOC.html
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Movement of Large Molecules

• Insulin stimulates increase in number of glucose
  transporters at membrane surface
• Increase number of transporters increases
  diffusion rate
• Driving force (phosphorylation) remans the same
• Low insulin levels decrease the number of glucose
  transporters at membrane surface
• Portions of membrane with transporters
  endocytose, trapping the transport protein in a
  vesicle
• Vesicle cannot refuse with membrane until insulin
  levels increase

http//www.uic.edu/classes/bios/bios100/lectf03am/
glucinsulin.jpg
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Movement of Large Molecules

• Phagocytosis
• cell wraps pseudopodia around the substance and
  packages it within a large vesicle formed from
  the membrane
• Pinocytosis
• cell takes in small droplets of extracellular
  fluid in small vesicles no target molecules in
  this process

http//www.emc.maricopa.edu/faculty/farabee/BIOBK/
BioBookTOC.html
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Movement of Large Molecules

• Receptor-mediated endocytosis
• very specific ligands (specific substances)
  bind to specific receptors on the cells surface
  (in coated pits) and this causes a vesicle to
  form around the substance and then to pinch off
  into the cytoplasm

http//cellbio.utmb.edu/cellbio/membrane.htm
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Summary
 
H20
O, CO2