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Supercoiled structure of linear DNA molecules with constrained ends. The helical nature of the DNA duplex is omitted for clarity. DNA supercoiling refers to the amount of twist in a particular DNA strand, which determines the amount of strain on it. A given strand may be "positively supercoiled" or "negatively supercoiled" (more or less tightly ...
A plasmid is a small, ... Supercoiled (or covalently closed-circular) ... supercoiled DNA migrates faster through a gel than linear or open-circular DNA.
Forms of DNA – Supercoiled plasmid have a slightly better transformation efficiency than relaxed plasmids – relaxed plasmids are transformed at around 75% efficiency of supercoiled ones. [7] Linear and single-stranded DNA however have much lower transformation efficiency.
Due to its extensive use as a cloning vector in research and industry, pUC19 is frequently used in research as a model plasmid. [10] For example, biophysical studies on its naturally supercoiled state have determined its radius of gyration to be 65.6 nm and its Stokes radius to be 43.6 nm.
Due to the supercoiled nature of plasmid DNA, strands of the circular DNA are able to remain together. Sodium dodecyl sulfate detergent is an anionic detergent that inserts itself into the phospholipid bilayer, disrupting the hydrophobic interactions that make up the membrane. Sodium Hydroxide and SDS detergent lyse the cell and release its ...
A plasmid is tightly wound into a negative supercoil (a). To release the intersecting states, the torsional energy must be released by utilizing nicks (b). After introducing a nick in the system, the negative supercoil gradually unwinds (c) until it reaches its final, circular, plasmid state (d).
The circular nature of the E. coli chromosome makes it topologically constrained molecule that is mostly negatively supercoiled with an estimated average supercoiling density (σ) of -0.05. [93] In the eukaryotic chromatin , DNA is found mainly in the toroidal form that is restrained and defined by histones through the formation of nucleosomes.
In a normal plasmid DNA preparation, multiple forms of DNA may be present. [13] Gel electrophoresis of the plasmids would normally show the negatively supercoiled form as the main band, while nicked DNA (open circular form) and the relaxed closed circular form appears as minor bands.