describe the structure of a 30nm chromatin fiber
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Answer:
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Explanation:
The structure of the 30-nm fibre is a key element in understanding chromatin compaction. It consists of a helical array of nucleosomes, each comprising a core particle wrapping ∼146 or 147 base pairs (bp) of DNA associated with a linker histone. The globular domain of the linker histone constrains an additional ∼20 bp (Allan et al, 1984), and the resulting chromatosomes are connected by stretches of linker DNA with lengths varying between 0 and ∼70 bp. At the core of current and past controversies is the structural problem of accommodating variable linker lengths between neighbouring core particles.
One characteristic of linker lengths is that in vivo they are usually quantized in increments of 10 bp (Strauss & Prunell, 1983; Widom, 1992), such that linker lengths of 20, 30 and 40 bp correspond to nucleosome repeat lengths of 167, 177 and 187 bp, respectively. The 10-bp increment is close to the 10.5-bp helical repeat of DNA in solution, which implies that, in principle, optimization of the total DNA twist between nucleosomes is an important feature of the structural organization of chromatin. This twist constraint further implies that optimal and uniform linker lengths could facilitate the folding of a nucleosome array
Answer:
Properties of the 30-nm fibre
The structure of the 30-nm fibre is a key element in understanding chromatin compaction. It consists of a helical array of nucleosomes, each comprising a core particle wrapping ∼146 or 147 base pairs (bp) of DNA associated with a linker histone.