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The term plasmid was coined in 1952 by the American molecular biologist Joshua Lederberg to refer to "any extrachromosomal hereditary determinant." [11] [12] The term's early usage included any bacterial genetic material that exists extrachromosomally for at least part of its replication cycle, but because that description includes bacterial viruses, the notion of plasmid was refined over time ...
Circular DNA is DNA that forms a closed loop and has no ends. Examples include: Plasmids, mobile genetic elements; cccDNA, formed by some viruses inside cell nuclei; Circular bacterial chromosomes; Mitochondrial DNA (mtDNA) Chloroplast DNA (cpDNA), and that of other plastids; Extrachromosomal circular DNA (eccDNA)
DNA gyrase is not the sole enzyme responsible for decatenation. In an experiment by Zechiedrich, Khodursky and Cozzarelli in 1997, it was found that topoisomerase IV is the only important decatenase of DNA replication intermediates in bacteria. [20] When DNA gyrase alone was inhibited, most of the catenanes were unlinked.
DnaA is a protein that activates initiation of DNA replication in bacteria. [1] Based on the Replicon Model, a positively active initiator molecule contacts with a particular spot on a circular chromosome called the replicator to start DNA replication. [2] It is a replication initiation factor which promotes the unwinding of DNA at oriC. [1]
This is a loop of both strands of the chromosome which are joined to an earlier point in the double-stranded DNA by the 3' strand end invading the strand pair to form a D-loop. The joint is stabilized by the shelterin protein POT1. [12] The T-loop, which is completed by the D-loop splice, protects the end of the chromosome from damage. [13]
Loops; Junctions; The antiparallel strands form a helical shape. [3] Bulges and internal loops are formed by separation of the double helical tract on either one strand (bulge) or on both strands (internal loops) by unpaired nucleotides. Stem-loop or hairpin loop is the most common element of RNA secondary structure. [8]
In archaea, the DNA in chromosomes is even more organized, with the DNA packaged within structures similar to eukaryotic nucleosomes. [30] [31] Certain bacteria also contain plasmids or other extrachromosomal DNA. These are circular structures in the cytoplasm that contain cellular DNA and play a role in horizontal gene transfer. [5]
Prokaryotic DNA Replication is the process by which a prokaryote duplicates its DNA into another copy that is passed on to daughter cells. [1] Although it is often studied in the model organism E. coli, other bacteria show many similarities. [2] Replication is bi-directional and originates at a single origin of replication (OriC). [3]