chapter6structureofdnaandrna(編輯修改稿)
2025-02-27 20:28 本頁(yè)面
【文章內(nèi)容簡(jiǎn)介】 ) (melting point) (熔點(diǎn) ) 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 requiring 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 topoisomerase? 2. The functional difference of the two types of topoisomerases? 3. The working mechanism of topoisomerase DNA TOPOLOGY (4) RNA STRUCTURE RNA STRUCTURE (1) RNA contains ribose and uracil and is usually singlestranded Biological roles of RNA 1. RNA is the geic material of some viruses 2. RNA functions as the intermediate (mRNA) between the gene and the proteinsynthesizing machinery. 3. RNA functions as an adaptor (tRNA) between the codons in the mRNA and amino acids. 4. RNA serves as a regulatory molecule, which through sequence plementarity binds to, and interferes with the translation of certain m
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