plasmidien

Plasmidien is a term used to describe plasmids, small circular double-stranded DNA molecules that replicate independently of the chromosomal DNA in a cell. They occur predominantly in bacteria, but are also found in some archaea and in the organelles of eukaryotic cells, such as mitochondria and chloroplasts. Plasmidien DNA carries accessory genes that can provide selective advantages under certain conditions, such as resistance to antibiotics or the ability to metabolize unusual substrates.

Plasmidien differ from chromosomal DNA in their replication and maintenance. They contain an origin of replication and are maintained by host cell machinery. Copy number varies from a single copy to dozens per cell, and stable inheritance during cell division often depends on partitioning systems or selective pressure that preserves the plasmid.

Classification of plasmidien includes factors such as incompatibility groups, which reflect replication control interactions, host range (narrow versus broad), and transfer capability (conjugative versus non-conjugative). Many plasmids carry genes that influence host physiology, metabolism, or virulence, but their essential genes are usually absent under standard growth conditions.

In research and biotechnology, plasmidien vectors are widely used to clone, propagate, and express genes. They commonly contain an origin of replication, a multiple cloning site, and selectable markers, enabling gene function studies and the production of recombinant proteins. Conjugative plasmids encode machinery for transfer between cells, contributing to horizontal gene transfer and the spread of traits such as antibiotic resistance among bacterial populations.

Safety and ethics considerations address the environmental release and regulation of plasmidien-bearing organisms, as well as potential impacts on public health and ecosystems. The concept dates to mid-20th-century discoveries by scientists including Joshua and Esther Lederberg.