Ch 13 Text 3

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  1. ·         Carriers are proteins that __; it involves both __ and the __, limiting the maximum rate at which transport can occur
    • transport ions or molecules across the membrane without hydrolysis of ATP
    • large conformational changes
    • interaction of the protein with only a few molecules per transport cycle
  2. ·         They can’t __ but can couple the __to the __, referred to as __; and, the carriers that move ions or molecules “uphill” in this way are __ or __
    • actively transport
    • thermodynamically unfavorable flow of one species of ion or molecule up a concentration gradient 
    • favorable flow of one species of ion or molecule up a concentration gradient
    • secondary active transport
    • secondary transporters or cotransporters
  3. o   They can be either __ or __
    §  Antiporters __
    §  Symporters __
    antiporters or symporters

    couple the downhill flow of one species to the uphill flow of another in the opposite direction across the membrane

    use the flow of one species to drive the flow of a different species in the same direction across the membrane
  4. ·         Members of the largest family have __that arose by duplication and fusion of the membrane protein with 6 transmembrane helices.
    o   Ex: lactose permease—a __that uses the__ across the E. coli membrane generated by the __ to drive the uptake of lactose and other sugars against a concentration gradient. 
    • 12 transmembrane helices 
    • symporter 
    •  H+ gradient
    • oxidation of fuel molecules
  5. ·         Structure of lactose permease: the structure consists of __, each of which comprises__, some of which are __. 
    o   The two halves are __ and __ by a single stretch of polypeptide; and, the sugar lies__ and is accessible from a path that leads from the __of the cell. 
    • two halves
    • six membrane-spanning alpha helices
    • irregular

    • separated and joined
    • in a pocket in the center of the protein

  6. ·         Mechanism for symporter action: 
    step one
    o   Cycle begins with the two halves oriented so that the opening to the binding pocket faces outside the cell; a proton form outside the cell binds to a residue in the permease
  7. ·         Mechanism for symporter action: 
    step two
    o   In the protonated form, the permease binds lactose from outside the cell
  8. ·         Mechanism for symporter action: 
    step three
    o   The structure everts to the form observed in the crystal structure
  9. ·         Mechanism for symporter action: 
    step four and five
    • o   The permease releases lactose to the inside of the cell, then a proton inside.
    • o   The permease everts to complete the cycle 
  10. ·         The site of __likely changes in the course of the cycle
Card Set:
Ch 13 Text 3
2014-11-08 18:49:18
Test Three
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