DNA Structure and Replication

ID #2344

Could you please check if I have the relative sizes of the following structures arranged correctly: {(Nuclease=Nucleosome=Kornberg Nucleosome) <(Chromatosome)< (Euchromatin) < (Heterochromatin)}=Chromosome

I don't know if I entirely follow your use of symbols in the statement that you listed, so I will do my best to clarify the information on chromatin. A nuclease (which is an enzyme that breaks phosphodiester bonds in nucleic acids, in this case DNA) was utilized by Roger Kornberg to digest chromatin, and he isolated core nucleosomes, which contained 8 histones (2 copies each of H2A, H2B, H3, and H4) and 147 bp of DNA. A chromatosome contains 2 copies of H2A, H2B, H3, and H4, plus H1 and 166 bp of DNA. Euchromatin is chromatin that is compacted 30nm or less, and heterochromatin is chromatin that is compacted greater than 30nm (but not including 30nm). The definition of chromosome as presented in the Cooper book is "A carrier of genes, consisting of long DNA molecules and associated proteins." Parts of your statement are accurate, but make sure that you are clear on the differences between nucleosomes, chromatosomes, euchromatin, and heterochromatin, and that you understand Kornberg's experiment. Section 5.2.1 in the Cooper book explains chromatin very well, so you may want to look that over as you are studying. 

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