Nucleosomes: beads on a string
Nucleosomes: beads on a string
Higher level packaging models N。 scaffold protein 20 A in diameter Loop 100A chromatin Nonhistone scaffold 300A proteins Additional nonhistone c scaffold components Rosettes compressed into a compact bundle Interphase Metaphase chromosome chromatin
EM picture supports the radial loop- scaffold model SARs: scaffold-associated reglons Agure 11.5 Experimental support for the radial loop- Fi affold model. a close-up of the image in Fig 11.2, this electron
EM picture supports the radial loopscaffold model. SARs: scaffold-associated regions
TABLE 11.2 The Different Levels of Chromosome Compaction Mechanism Status what it Accomplishes Nucleosome Confirmed by crystal structure Condenses naked dna 7-fold to a 100-A fiber Supercoiling Hypothetical model (the 300-A fiber predicted Causes additional 6-fold compaction, achieving a by the model has been seen in the electron 40-to 50-fold condensation relative to naked dna microscope) Radial loops--scaffold Hypothetical model (preliminary experimental Through progressive compaction of 300-A fiber, support exists for this model) condenses dna to rodlike mitotic chromosome that is 10,000 times more compact than naked DNA
Specialized chromosomal elements Replication Telomere Centromere
Specialized chromosomal elements • Replication • Telomere • Centromere