武漢大學(xué)分子生物學(xué)全部課程3(編輯修改稿)
2025-02-27 02:40 本頁面
【文章內(nèi)容簡介】 ure of DNA under physiological conditions ?A form (11 bp/turn), which observed under the condition of low humidity, presents in certain DNA/protein plexes. RNA double helix adopts a similar conformation. DNA strands can separate (denature) and reassociate (anneal) DNA STRUCTURE (8) Key terms to understand (melting point) DNA TOPOLOGY DNA TOPOLOGY (1) Structure (1): Linking number is an invariant topological property of covalently closed, circular DNA (cccDNA) Linking number is the number of times one strand have to be passed through the other strand in order for the two strands to be entirely separated from each other. Species of cccDNA 1. Plasmid and circular bacterial chromosomes 2. Linear DNA molecules of eukaryotic chromosomes due to their extreme length, entrainment in chromatin and interaction with other cellular ponents (Ch 7) Structure (2): Linking number is posed of Twist and Writhe The linking number is the sum of the twist and the writhe. Twist is the number of times one strand pletely wraps around the other strand. Writhe is the number of times that the long axis of the double helical DNA crosses over itself in 3D space. DNA TOPOLOGY (2) Local disruption of base pairs Function (1): DNA in cells is negatively supercoiled。 nucleosomes introduces negative supercoiling in eukaryotes Negative supercoils serve as a store of free energy that aids in processes that require strand separation, such as DNA replication and transcription. Strand separation can be acplished more easily in negatively supercoiled DNA than in relaxed DNA DNA TOPOLOGY (3) Function (2): Topoisomerases (P115119) 1. The biological importance of
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