plazmák

Plazmák, or plasmids, are small, typically circular double‑stranded DNA molecules that exist independently of the chromosomal DNA in many bacteria and some archaea and eukaryotes. They replicate autonomously, usually using their own origin of replication, and their copy number can vary from a few to hundreds per cell depending on the plasmid and host.

Most plasmids are not essential for basic growth, but they often carry genes that confer selective advantages under certain conditions. Common traits include antibiotic resistance, heavy‑metal tolerance, or specialized metabolic capabilities. Plazmák can influence host biology by altering gene expression and metabolism, and they can be lost or gained through cell division or horizontal gene transfer.

In biotechnology and research, plazmák are widely used as vectors to introduce and propagate foreign DNA in cells. Plasmid vectors typically feature an origin of replication (ori), a selectable marker such as an antibiotic resistance gene, and a multiple cloning site for inserting new DNA. Some vectors also include reporter genes, regulatory elements, or sequences that enhance stability.

Transfer between cells often occurs via conjugation, a process where plasmids move through a pilus from donor to recipient. Plazmák can also spread through transformation (uptake of free DNA) or transduction (DNA transfer by viruses).

Classification often involves incompatibility groups (Inc), with examples like F plasmids that govern conjugation and R plasmids that carry resistance genes. Ti plasmids from Agrobacterium are notable for plant genetic engineering. Applications span cloning, protein expression, gene therapy research, and agricultural biotechnology, all pursued with attention to biosafety and ethical considerations.