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7.4

7.4. Dr. Laurie Solis. Facilitated Diffusion: Passive Transport Aided By Proteins. When transport proteins assist molecules in passing through the lipid bilayer , we call this facilitated diffusion. Why is this important in the human body?. Take your kidney’s for example.

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7.4

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  1. 7.4 Dr. Laurie Solis

  2. Facilitated Diffusion: Passive Transport Aided By Proteins • When transport proteins assist molecules in passing through the lipid bilayer, we call this facilitated diffusion

  3. Why is this important in the human body? • Take your kidney’s for example. • Kidney cells have a lot of water channel proteins (aquaporins) – they allow water to pass through the membrane

  4. Why is this important in the human body? • Aquaporins facilitate massive amounts of diffusion; • This allows them to reclaim water from the urine before it is excreted • If the kidneys did not work this way, a person would have to drink 50 gallons of water a day and excrete 50 gallons of water a day to stay healthy.

  5. Other channel proteins • Ion channels : function as gated channels • Open and close in response to a stimulus

  6. Active Transport uses energy to move solutes against their gradients • To pump a molecule across a membrane against its gradient requires work • The cell must expend energy • This is called active transport

  7. Active Transport uses energy to move solutes against their gradients • This is called active transport • Active transport uses carrier proteins, not channel proteins

  8. All cells have voltages… • All cells have voltages across their plasma membranes • Voltage is “electrical potential energy” • Cytoplasm = negative charge • Voltage across a membrane = membrane potential • Membrane potential = acts like a battery • Two forces/actions drive ions across a membrane: • Chemical • Electrical • Electrochemical gradient

  9. Electrogenic pump • Electrogenic pump: a transport protein that generates voltage across a membrane • In animal cells = sodium-potassium pump • In plant cells = proton pump • These store energy that can be tapped for celllular work • Proton gradients in the cell is ATP during cellular respiration

  10. Electrogenic pump

  11. Proton pump • http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_the_sodium_potassium_pump_works.html

  12. Cotransport • Cotransport – involves a single ATP powered pump that transports a specific solute and indirectly drives the active transport of several other solutes in a mechanism

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