water lipid bilayer water
.质 膜 的 超 微 结 构 ◼ 单位膜(Unit membrane) 电镜下膜的剖面,表现为两条 暗带夹一明带的结构，厚为70-100Å
.质 膜 的 超 微 结 构 ◼ 单位膜(Unit membrane) 电镜下膜的剖面,表现为两条 暗带夹一明带的结构，厚为70-100Å
染色质 核膜外层 核膜内层 核 孔 核 仁 核 孔 细胞核的超微结构（示意图）
间距3nm DNA wound around a cluster of histone molecules 核小体 Linker DNA Histone 2.5nm 组蛋白1 DNA双螺旋 组蛋白复合体 Nucleosome 1Inm 5.5nm Figure 4.7 图2-25一条伸展的染色质丝的一部分， Histone proteins associate into short cylinders;then DNA winds around each 示其核小体的结构 cylinder.The DNA-histone particles then associate into a compact arrangement. (引自Goodwin and Mercer,1983)
nucleosome DNA highly condensed looped threadkke chromosome form domains chromosome form the metaphase chromasome Figure 17.5 A current model of chromosome structure,based on studies of electron micrographs of the sonshown here(bottom row).Each nucleosome consists o DNA wound as a double-stranded thread on an individual spool of histone molecules.The DNA loops around each spool In an unknown way further levelof folding lead to the condensed formof the metaphase chromosome