??????? TRANSPORT OF IONS AND SMALL MOLECULES ACROSS CELL MEMBRANES

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???????TRANSPORT OF IONS AND SMALL MOLECULES
ACROSS CELL MEMBRANES

• ????Membrane Transport

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Relative permeability of a pure
phospholipidbilayer to various molecules
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????????????????????Membrane Proteins Mediate
Transport of Most Molecules and All Ions Across
Biomembranes

• ATP-? ATP-powered pumps
• Light-driven pump
• ???? Channel proteins
• ????Transporters (also called carriers)
• Uniporters
• antiporters and symporters
• Water and urea is frequently accelerated by
  specific proteins because their transport by
  passive diffusion usually is not sufficiently
  rapid to meet cellular needs.

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Overview of membrane transport proteins
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• ????
• ????
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• Membrane Proteins Mediate Transport of Most
  Molecules and All Ions Across Biomembranes
• Water and urea is frequently accelerated by
  specific proteins because their transport by
  passive diffusion usually is not sufficiently
  rapid to meet cellular needs.

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• ?????????

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• ATP?????????
• ???
• ??????
• ????(cotransport)- ATP????
• ???(symport)
• ????(antiport)
• ???(??)

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?????3???
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Uniporters,?GLUT(???????)??

• ???????,?????????????????
• ??
• ??
• ??

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GluTsGlucose transporter
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• The human genome encodes 12 proteins,
  GLUT1GLUT12, that are highly homologous in
  sequence, and all are thought to contain 12
  membrane-spanning helices.

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• ??????????????????????????ATP???????
• ???
• ??(???)?????????,Na??
• ????
• ????pH???,Na??H

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Na??????????
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2???????????
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Antiporter

• Na -Linked Antiporter Exports Ca2 from Cardiac
  Muscle Cells

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???????pH?antiporter
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???,??1ATP,??3?Na,??2?K
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??,??1ATP,??2?Ca2,
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???

• H?,
• ????????,??H?,?H?????
• ATP???,??????

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ABC??

• Bacterial Permeases Are ABC Proteins That Import
  a Variety of Nutrients from the Environment
• About 50 ABC Small-Molecule Pumps Are Known in
  Mammals

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????????????Nongated Ion Channels andthe
Resting Membrane Potential
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???????

• ????????????????????

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• Patch Clamps Permit Measurement of Ion Movements
  Through Single Channels

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???????????Voltage-Gated Ion Channelsand the
Propagation of ActionPotentials in Nerve Cells
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• ????????????????????
• ????
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• ??????????????????
• 1,32
• 2,K?????

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• ????
• ???????????????
• ?????,?????????????,?????????????
• ???????,?????????,???????

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?

• ???
• Osmotic Pressure Causes Water to Move Across
  Membranes

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Aquaporins Increase the Water Permeabilityof
Cell Membranes

• ??????
• ?????????,????????????????

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???????
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?????????

• ??(receptor)
• ?????(adaptin)
• ????(clathrin)

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????clathrin,?????

• ?????????????????,?????????????
• ???????????????

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• ??????
• ????????,????????????????
• LDL???????????

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• 1,???
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