Plasmid – The most commonly used vector in genetic engineering. It is a smaller DNA molecule that can autonomously replicate, typically attached to the cell's non-chromosomal or nuclear region DNA (also known as the cell’s extrachromosomal DNA). Most plasmids are closed, circular, double-stranded DNA molecules.
A plasmid vector is an artificially constructed plasmid designed for laboratory use based on natural plasmids. Compared to natural plasmids, plasmid vectors usually carry one or more selective marker genes (such as antibiotic resistance genes) and an artificially synthesized multiple cloning site (MCS) with several restriction enzyme recognition sites. Non-essential sequences are removed to minimize the molecular weight, facilitating genetic engineering operations.
Plasmids can be obtained in large quantities through plasmid amplification. This typically involves transforming the bacterial plasmid into Escherichia coli (competent cells), then using E. coli to amplify the plasmid through bacterial culture. The plasmid is then harvested by extraction methods. Only a small amount of plasmid (1µg) is needed for amplification, making plasmid reuse very convenient. Therefore, after plasmid shipment, there will be no returns or exchanges if there are no sequence issues.
