Testingand Thinking广Gorter and Grendel's classic conclusion that the plasmamembrane of the human erythrocyte consists of a lipid bilayerwas based on the following observations:thelipids that they extracted with acetone（丙酮)from 4.74x10ierythrocytes formed a monolayer 0.89 m? in area when spreadout on a water surface; andthe surface area of one erythrocyte was about 100μm?ii)according to their measurementsShow from these data how they came to the conclusion that the(a)erythrocyte membrane is a bilayer.(b)We now know that the surface area of a human erythrocyte isabout145μm2.Explain how Gorter and Grendel could have come to the rightconclusion when one of their measurements was only abouttwo-thirds of the correct value
1 Testing and Thinking 1. Gorter and Grendel's classic conclusion that the plasma membrane of the human erythrocyte consists of a lipid bilayer was based on the following observations: (i) the lipids that they extracted with acetone(丙酮 ) from 4.74 ×109 erythrocytes formed a monolayer 0.89 m2 in area when spread out on a water surface; and (ii) the surface area of one erythrocyte was about 100μm2 , according to their measurements. (a) Show from these data how they came to the conclusion that the erythrocyte membrane is a bilayer. (b) We now know that the surface area of a human erythrocyte is about 145μm2 . Explain how Gorter and Grendel could have come to the right conclusion when one of their measurements was only about two-thirds of the correct value
AnswersforTesting(a)Ifthelipidsfrom4.74x10erythrocyteshaveanarea of0.89m?(=0.89x1012uum2).then each cell has a monolayerarea of 0.89 x 1012/4.74 x 109-188 μm2.This is almost twicethe surface area of an erythrocyte as Gorter and Grendelestimated it at the timeleadingto the conclusion that thesurface of each cell was covered with two layers (i.e., abilayer)of lipid.(b)Asitturned out,thelipid extractiontechniquethatGorterand Grendel used was not quantitative, so theyunderestimated the amount of lipid per cell. In fact, theyextracted only about two-thirds of the total lipid from theerythrocytes,so both of their values were offby about thesame extent-a classic case of the right conclusion but fromflaweddata
2 Answers for Testing (a) If the lipids from 4.74 x 109 erythrocytes have an area of 0.89 m2 (= 0.89 x 1012 μum2 ). then each cell has a monolayer area of 0.89 x 1012/4.74 x 109 = 188 μm2 .This is almost twice the surface area of an erythrocyte as Gorter and Grendel estimated it at the time, leading to the conclusion that the surface of each cell was covered with two layers (i.e., a bilayer) of lipid. (b) As it turned out, the lipid extraction technique that Gorter and Grendel used was not quantitative, so they underestimated the amount of lipid per cell. In fact, they extracted only about two-thirds of the total lipid from the erythrocytes, so both of their values were off by about the same extent—a classic case of the right conclusion but from flawed data
保证内环境的相对稳定。防止胞外物质自由进入细胞，细胞必须与周围环境发生信息、物质与能量的交换，才能完成特定的细胞膜生理功能。因此细胞必须具备一套物质转运体系，用来获得所需物质和排出代谢废物3.5细胞质膜的物质运输3.5物质的跨膜运输【P102】【王金发，P391-409】大分子和颗9.5细胞分泌与内吞作用膜泡运输粒物质运输9.6小泡运输的分子机制质膜物质运输离子和一些穿膜运输小分子运输据估计，膜上与物质转运有关的蛋白占核基因编码蛋白的15~30%，能量达细胞总消耗能量的三分之二
3 3.5 细胞质膜的物质运输 质膜物质运输 穿膜运输 膜泡运输 离子和一些 小分子运输 大分子和颗 粒物质运输 3.5 物质的跨膜运输【P102】 【王金发，P391-409】 9.5 细胞分泌与内吞作用 9.6小泡运输的分子机制 细胞膜 防止胞外物质自由进入细胞，保证内环境的相对稳定。 细胞必须与周围环境发生信息、物质与能量的交换，才能完成特定的 生理功能。因此细胞必须具备一套物质转运体系，用来获得所需物质 和排出代谢废物 据估计，膜上与物质转运有关的蛋白占核基因编码蛋白的15~30%，能量达细胞 总消耗能量的三分之二
膜泡运输内吞外排pumpproteinlipidbilayer穿膜运输channelproteinprotein
4 内吞 外排 穿膜运输 膜泡运输
一膜泡运输亦称批量运输（bulktransport)。真核细胞通过内吞作用（endocytosis）和外排作用（exocytosis)形成包完成大分子与颗粒性物质的跨膜运输。在转运过程中，质膜内陷，围细胞外物质的囊泡，因此又称膜泡运输。①物质进出细胞始终由膜包围，在胞内形成小膜泡；特点②运输量大
5 一、膜泡运输 亦称批量运输(bulk transport)。 物质进出细胞始终由膜包围，在胞内形成 小膜泡； 运输量大。 特点 ① ② 真核细胞通过内吞作用（endocytosis）和外排作用（exocytosis） 完成大分子与颗粒性物质的跨膜运输。在转运过程中，质膜内陷，形成包 围细胞外物质的囊泡，因此又称膜泡运输