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W4 Ch11 Biological Membranes and Transport - Coggle Diagram
W4 Ch11 Biological Membranes and Transport
Lipids Aggregate into Structures
in Water
bilayers
有兩條fatty acid(phospholipid、sphingolipid)且為two leaflet，fatty acid在內層
liposomes
可由體外製成，cavity can
enclose dissolved molecules，useful artificial carriers
of molecules
micelles
有polar and nonplar端
Functions of Membranes
運輸運出(channel、gate、pump)
signaling(receptor)
隔出間隔
幫助ATP合成(enzyme)
membrane 特殊
Phosphatidylserine:通常在內層，若出現在外層，且在leukocyte則意味著activates blood clotting；在外層，且在其他cell則marks the cell for destruction
The outer leaflet is often more positively charged
Asymmetric
由非共價鍵的hydrophobic effect 所穩定
古細菌為monolayer of bifunctional lipids
外層多為charged residue(polar的環境)
Tyr、Trp會在膜介面處
內層為hydrophobic(較不帶電)
Archaea Have Multiple Unique
Membrane Constituents
branched isoprene chains in archaea；unbranched fatty acid chains in bacteria
古細菌為monolayer of bifunctional lipids
古細菌有L-glycerol；細菌有D-glycerol
ether linkages in archaea
ester linkages in bacteria
古細菌有isoprene分支及tetraethers likage (更穩定)，單層膜
Three Types of Membrane Proteins
Peripheral (non-GPI linked)
membrane proteins
1.其皆在membrane的polar head group
2透過ionic interaction與lipid的head group或integral protein接上(weak)
3.可透過change pH輕易脫下
Lipid-linked Membrane Proteins()
Amphitrophic Membrane Proteins
1.可與membrane透過covalent結合或透過醣(GPI-protein)，which可被phospholipase C切下，接在menbrane。
2.會受biological regulation
Integral Membrane Proteins(穿模蛋白):
1.asymmetry
2.透過membrane的fatty acid和protein的hydrophobic處有tight interaction
3.穿過一層膜稱monotopic；兩層膜為polytopic
4.removed by detergents(清潔劑)後仍會有fatty acid插在protein上
Farnesylation of Proteins:
1.目的為脂化蛋白
2.需有CaaX序列方可進行Farnesylation，C:Cys；a:脂肪族AA；“X” is Met, Ser, Glu, or Ala
3.由farnesyl transferase催化
4.有些蛋白不經此步驟無法達成特定事件
Membrane Phases
liquid-ordered state (gel phase膠態(低溫))
liquid-disordered state (fluid phase流態(高溫))
gel phase 經加熱變 fluid phase，正常生理狀態多為fluid phase，才能有proper function
Membrane fluidity取決於fatty acid composition 和 m.p
fluid phase在fatty acid越短、且多為unsaturated(有彎角流速較快)時則易達成
高溫⇒fluid phase，需要長、飽和的fatty acid以降低流動性
低溫⇒gel phase，需unsaturated fatty acid增加流動性
Cell membranes of many
eukaryotes contain sterols
1.cholesterol in animals
2.phytosterols in plants
3.ergosterol in fungi
Cell membranes of aerobic prokaryote 有 hopanols
Membrane dynamics
Lateral diffusion(橫向)很快
Tranverse diffusion(上下置換)則非常慢，需透過酵素Flippase
(需消耗ATP)，而此酵素可分為三種
1.Flippase:上到下
2.Floppase:下到上
3.scramblase:上到下或下到上皆可
Membrane Rafts:
1.contain clusters of glycosphingolipids with longer-than-usual tails
2.are more ordered
3.contain specific doubly or
triply acylated proteins
4.allow segregation of
proteins in the membrane
神經傳導物質囊泡融合調控的蛋白
T-SNARE assemble on the
target membrane
V-SNARE assemble on the
vesicle membrane.
Q-SNARE (e.g., SNAP-25) are regulatory proteins that are
Ca2+ induced.
Types of Transport
促進性擴散
Primary active transport
被動擴散
secondary active transport :跟primary 差別在於是消耗其他通道的ATP達成主動運輸
transport system:
1.uniport:單一物質進入
2.symport:兩種物質進入
3.Antiport:一種物質進入；一種物質輸出
ABC Transporters Use ATP Hydrolysis
to Drive Transport of Substrates