糖脂 -含量<5% 神经细胞糖脂含量较高 胆固醇 真核细胞膜 含量<30% YOUR ACCO
• 糖脂 – 含量＜5％ – 神经细胞糖脂含量较高 • 胆固醇 – 真核细胞膜 – 含量＜30%
Figure 11-10 Comparison of a fat mole- cule(triacylglycerol)and a phospholipid molecule(phosphatidylethanolamine). The hydrophobic parts are shaded gray, CH,-NH and the hydrophilic parts are shaded pink. The fat molecule is entirely hydrophobic. whereas the phospholipid molecule is amphipathic.(The third hydrophobic tail C=0 of the triacylglycerol molecule is drawn here facing upward for comparison with the phospholipid,although normally it is CH2- CH-CH2 CH2一CH-CH2 depicted facing down.) 0 C=0 C=0 C=O C=O triacylglycerol phosphatidylethanolamine
磷脂 hydrophilic head hydrophobic tails Figure 11-5 A schematic drawing of a typical membrane lipid molecule. YUUR
磷脂
Figure 11-6 A phosphatidylcholine mole cule.It is represented (A)schematically. (B)in formula.(C)as a space-filling model. and (D) as a symbol.This particular phos- pholipid is built from five parts:the hydrophilic head,choline,is linked via a phosphate to glycerol,which in turn is linked to two hydrocarbon chains,forming the hydrophobic tail.The two hydro- carbon chains originate as fatty acids that is.hydrocarbon chains with a-COOll group at one end-which become attached to glycerol via their-COOH groups.A kink in one of the hydrocarbon chains occurs where there is a double bond between two carbon atoms:it is exaggerated in these drawings for empha sis.The phtosphatidyl-part of the name of phospholipids refers to the phosphate- glycerol-fatty acid portion of the molecule CHOLINE ead PHOSPHATE GLYCEROL 88be HYDRO RBON 心 IA) 6
bilayer confer on that bilayer a self-sealing property.Any tear in the Figure 11-11 A phospholipid bilayer bilayer will create a free edge with water,and because this is energeti- seen in cross-section.(A)Computer simu- cally unfavorable,the molecules of the bilayer will spontaneously re- lation showing the phospholipid mole- arrange to eliminate the free edge.If the tear is small,this spontaneous cules (red tails and yellow heads)and rearrangement will lead to the repair of the bilayer,restoring a single the surrounding water molecules(blue). (B)Schematic drawing of a phospholipid continuous sheet.If the tear is large,the sheet may break up into sepa- bilayer in water.(A,adapted from Science rate vesicles.In either case,the overriding principle is that free edges are 262:223-228(1993),courtesy of R.Venable quickly eliminated. and R.Pastor.) water bilaye water A (B) 1 nm