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After introducing a nick in the system, the negative supercoil gradually unwinds (c) until it reaches its final, circular, plasmid state (d). [2] Nicked DNA can be the result of DNA damage or purposeful, regulated biomolecular reactions carried out in the cell. During processing, DNA can be nicked by physical shearing, over-drying, or enzymes.
A plasmid is a small, extrachromosomal DNA molecule within a cell that is physically separated from chromosomal DNA and can replicate independently. They are most commonly found as small circular, double-stranded DNA molecules in bacteria ; however, plasmids are sometimes present in archaea and eukaryotic organisms .
Using the unnicked strand as a template, replication proceeds around the circular DNA molecule, displacing the nicked strand as single-stranded DNA. Displacement of the nicked strand is carried out by a host-encoded helicase called PcrA (the abbreviation standing for plasmid copy reduced) in the presence of the plasmid replication initiation ...
Genetic and biochemical studies have shown that the helicase is essential for plasmid rolling-circle replication and repair of DNA damage caused by exposure to ultraviolet radiation. It catalyzes the unwinding of double-stranded plasmid DNA that has been nicked at the replication origin by the replication initiation protein.
DNA Pol I has a 5′ to 3′ exonuclease activity in addition to its polymerase activity, and uses its exonuclease activity to degrade the RNA primers ahead of it as it extends the DNA strand behind it, in a process called nick translation. Pol I is much less processive than Pol III because its primary function in DNA replication is to create ...
A relaxase is a single-strand DNA transesterase enzyme produced by some prokaryotes and viruses. Relaxases are responsible for site- and strand-specific nicks in unwound double-stranded DNA . Known relaxases belong to the rolling circle replication (RCR) initiator superfamily of enzymes and fall into two broad classes: replicative (Rep) and ...
Those colored shapes are called “printer’s color blocks” or “process control patches,” and they’re there to help the printing team who prints the food packaging.
Drawing showing the difference between a circular DNA chromosome (a plasmid) with a secondary helical twist only, and one containing an additional tertiary superhelical twist superimposed on the secondary helical winding. In nature, circular DNA is always isolated as a higher-order helix-upon-a-helix, known as a superhelix. In discussions of ...