Membrane Structure and Function

1
Membrane Structure and Function
2
Membranes Structure
Membrane ???????????????????? ?????? Lipids Prot
ein ??? Carbohydrates
3
Membrane models
??????????????????????????????? membrane model
????? ????????????????????????????????????????????
???
4
Artificial membranes (cross section)
Hydrophobic tail
Hydrophilic head
5
Two generations of membrane models
6

• The Davson-Danielli model (1935 1970)

7
(b) Current fluid mosaic model
8
Freeze fracture and freeze-etch
9
The fluidity of membranes
(a) Movement of phospholipids
(b) Membrane fluidity
10
(c ) Cholesterol within the membrane
Cholesterol ????????????????????????????
phospholipids ????? membrane ?????????????????????
??????? ??????????????????? cholesterol
????????????????? phospholipids ????? membrane
??????????
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???????????????????????????????
12
????????????????????? ?????????? phospholipid,
membrane protein, carbohydrates ??? cholesterols
?????????????????????????????????????? membrane
???????????? Fluid Mosaic Model ??????? Singer
??? Nicholson ???? ?.?. 1972 ?????????????? 1. me
mbrane ?????????? lipid bilayer
???????????????????? ???????????????????????????
??????????????????? mosaic (??????????????????????
??????????????????????) 2. ?? peripheral protein
?????????????????????? membrane
3. ??????????????????? oligopolysaccharide
chains ??? glygoproteins ??? glycolipids
????????????
13
The structure of transmembrane protein
14
Sidedness of plasma membrane
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??????? membrane ?? 2 ??????? cytoplasmic sides
(????????? cytoplasm) ??? extracellular sides
(???????????????) ?????????????????????
????????????????????????????????? membrane
????????????? ER ??? Golgi complex ??????????????
??? membrane ??? organelles ????????????????
organellles ?????????? extracellular sides
?????????????????????? cytoplasmic sides
?????????? carbohydrates ????????????? ER ???
modified ??? Golgi complex Vesicles ?????????
plasma membrane ?????? membrane ??????? vesicles
????????????? plasma membrane ????
????????????????????????????????? (??????)
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Some functions of membrane protein
Transport protein ?????????? ions
????????????????????????????????????????
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Enzymes
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Signal transduction ?????????????????????????????
??????????????????????????????????????????????????
?????????????????????????? ???? ???????
19
Intercellular junctions ????????????????? tight
junction ?????????????????????????????????????????
?
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Cell-cell recognition
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Attachment to the cytoskeleton and extracellular
matrix (ECM)
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??????????????????????????????? (Traffic Across
Membranes)
??????????????????????????????????????????????????
??????????????????????????????????????? ????????
selective permeability ???????????????????????????
??????????????????????????????????????????????????
?????????
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Selective permeability ???????????????????????????
? 1. Phospholipid bilayer    1.1
????????????????????? (nonpolar (hydrophobic)
molecules) ???? hydrocarbons ??? O2
??????????????????????????????????????????????????
?????????????????????? ???????????????????
?????????? 2 ?????????????????????????????????????
?????????????????????????????????  
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• 1.2 ?????????????????? (polar (hydrophilic)
  molecules)
•  ??????????????????????????????????????????
  (small, polar uncharged molecules)???? H2O, CO2
  ????????????????????????????? (synthetic
  membranes) ???????
•  ??????????????????????????????????????????
  (large, polar uncharged molecules) ????
  ???????????? ?????????????????????????????????
•  ????????????? (ions) ????????????????????????????
  ???? Na, H ???????? Hydrophobic bilayer ??????

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• -         2. Specific integral transport
  proteins
• ????????????? CO2 ??? ????????????????????
  (nonpolar molecules) ?????????????????????????????
  ?????????????????????????????????
• ??????????????????????????????????????????????????
  ??????????????????????????????????????????????????
  ????????????? ???????????????????????????
  transport proteins

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Diffusion and Passive transport ???????
(diffusion) ??????? ??????????????????????????????
??????????????????????????????????????????????????
???????????????????????????? ?????????????????????
?? (dynamic equilibrium) ????????????????????????
??????????????????????????????????????????????????
?????????????????????????
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?????????????????????????????????????????
???????? passive transport ???????????????????????
???????????????????????? ?????????????????????????
selective permeable ?????????????????????????????
????????????????? ??????????????????????????????
??????????????????????????????????????????????????
?????????
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?????????????????????????????????????????
(a) ??????????????????????????????????????????????
????????????????????????????????????????????
???????????????????????? (dynamic equilibrium)
??????????????????????????????????????????????????
??????????????????????????????????????????????????
?????????????????????
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(b) ????????? ????????????????? 2 ????
????????????????????????????????
?????????????????????????????????????????????
??????????????????????????????????????????????????
???
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???????????????????????????? ??????
???????????????? ?????????????????????????????????
??????????????????????????????????????????????????
???????? ?????????????????????????????????????????
?? ???????????????????????????????????????????????
???????????????
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Osmosis
Osmosis ?????????????????????????????????????????
??????????????????????????????????????????????????
?????? (hypoosmotic solution)?????????????????????
??????????????????????????????????????????
(hyperosmotic solution) ?????????????????????
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The water balance of living cells
??????????????????????????????????????????????????
?????????????????????????? ???????????????????????
???
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The contractile vacuole of Paramesium an
evolutionary adaptation for osmoregulation
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Facilitated diffusion
Transport proteins ???????????????????????????????
??????????????????????????????????????????????????
????????????????????????????? ????????????????????
facilitated diffusion ?????????????????????????
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Active transport ????????????????????????????????
????????????????????????????????????????????????
???????????????????? active transport
????????????????????? ATP ???????????? ????????
NA ???????????????? K ?????????????
???????????? Sodium-potassium pump
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The sodium-potassium pump
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Sodium-potassium pump ???????????????????? Na
???????????????????? transport protein ???? ATP
??????????????????????????????????????????????????
?? Na ??????????????????????? ??????????? K
???????????????? ?????????????????????????????????
????????? ????? K ?????????????????????
??????????????????????????????????????????????????
??????????????????????
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Diffusion
Passive transport
Facilitated transport
Active transport
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An electrogenic pump
Electrogenic pump ???? transport protein
???????????????????????????????????????????
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An electrogenic pump ???????????? Na/K pump
???? electrogenic pump ?????????????????????
Proton pump ???? electrogenic pump
??????????????????? ????????? ????????????
??????? mitochondria ??? chloroplasts ??? proton
pump ??????????????? ATP
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Cotransport
??????????????????????????? ATP pump
???????????????????????????? transport protein
???????????????????????????????????
???????????? ????????????? proton pump ???????
transport protein ????? sucroseH ?????????????
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Exocytosis and endocytosis transport large
molecules ??????????????????????? ???? ??????
??? ???????????? ?????????????????????????
??? exocytosis ?????????????????????????????
endocytosis
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Endocytosis ?? 3 ??? ??????        1.
Phagocytosis        2. Pinocytosis        3.
Receptor-mediated endocytosis
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Phagocytosis
Phagocytosis ???????????????????????????????????
???????????????? cytoplasm ???????????????????????
????????????????? ???? food vacuole ???? food
vacuole ?????????????? lysosome ???????????
hydrolytic enzymes ?????????????????????????
????????????????????????????
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Pinocytosis
Pinocytosis ???????????????????????????????????
???????????????????????????????????????????
?????????????????????? cytoplasm
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Receptor-mediated endocytosis
Receptor-mediated endocytosis ????????????????????
????????????????? ???????????????? receptor
???????????????????????????????
??????????????????????????????????
???????????????????? receptor ????????????????????
??????