核小体 Linker DNA Histones H2A Internal structure H2B, H3, H4 (two molecules each) 55A Core DNA Nudeosome H2B A H2A H2A H2B- H4 (b) 组蛋白八聚体 核小体 组蛋白H 塾
核小体
la) DNA Double Helis (c) Packing of Nucleosomes (d) Chromosomal Scaffolding (Solenoid Model) ()Helical Coiler 250nm topoisomerase Scaffolding Proteins (9) ) Metaphase e)Loops Chromosome Figure 9-3 A CHROMOSOME UNWOUND: FROM DNA TOCOLORED BODY A chromosome contains highly coiled and supercoiled DNA strands. (a, b)The DNA molecule is wound around clusters of eight proteins called histones, forming nucleosomes. (c) Nucleosomes are packed into cylinders called solenoid ld, e) Solenoids are thrown into loops attached by topoisomerase enzymes to a central scaffolding. (0 The loops and scaffold form a coiled rod, and (g) these coils are visible in chromosomes at metaphase, as this photo shows