Plasmids- Definition, Properties, Structure, Types, Functions, Examples


Plasmids are small circular DNA fragments that are found in many microorganisms, such as bacteria, archaea, and some eukaryotes. They are not part of the main chromosome of the cell, but they can replicate independently and carry genes that may confer some advantages to the host organism. Plasmids are also known as extra-chromosomal elements or genetic tools.

The term plasmid was coined by Joshua Lederberg in 1952, who discovered that some bacteria can exchange genetic material through a process called conjugation. He observed that some strains of Escherichia coli could transfer antibiotic resistance to other strains through a physical contact mediated by a hair-like structure called pilus. He proposed that this transfer was due to a circular DNA molecule that could move from one cell to another. He named this molecule plasmid, from the Greek word plasmos, meaning molded or formed.

Plasmids have been widely used in biotechnology and genetic engineering, as they can be manipulated to introduce, modify, or delete specific genes in the host cell. For example, plasmids can be used to produce recombinant proteins, such as insulin or human growth hormone, in bacteria or yeast cells. Plasmids can also be used to study gene expression and regulation, gene function and interaction, and gene therapy.