What Are Plasmids?

Plasmids are found in a wide range of organisms, including bacteria, actinomycetes, filamentous fungi, large fungi, yeast, plants, and even the human body. In terms of molecular composition, there are DNA plasmids and RNA plasmids; in terms of molecular configuration, wired plasmids and circular plasmids: their phenotypes are also diverse. Bacterial plasmids are the most commonly used vectors in genetic engineering. ^[1]

Basic Information

Chinese name

Plasmid

Foreign name

plasmid

Field

Microbiology, molecular biology, genetics

Plasmid classification

According to whether the plasmid can pass the conjugation effect of bacteria, it can be divided into zygosity plasmid and non-zygosity plasmid. Zygote plasmids carry genes involved in zygote transmission. Non-conjugating plasmids are delivered under the conditions by the induction or transduction of conjugating plasmids that coexist with them.

According to the type of plasmid replication in bacteria, it can be divided into two types: tightly controlled and relaxed controlled. The replication enzyme system that tightly controls the replication plasmid is shared with chromosomal DNA replication and can only be replicated at certain stages of the cell cycle. When the cell chromosome stops replicating, the plasmid will no longer replicate. The replication-enzyme line of the relaxation-controlled replication-type plasmid is not affected by the chromosomal DNA replication enzyme line, and can be replicated at any time during the entire cell growth cycle. The plasmid can continue to replicate when chromosome replication has stopped.

According to the incompatibility of the plasmid, it can be divided into incompatibility and compatibility. Incompatibility refers to the phenomenon that similarly structured, closely related plasmids cannot coexist stably in the same host bacteria, and vice versa. Commonly used in epidemiological investigations.

Plasmid function

The plasmid has the ability to replicate autonomously, so that it can maintain a constant copy number in the progeny cells and express the genetic information it carries. Bacterial plasmids are commonly used vectors in recombinant DNA technology. A vector is a tool that sends a useful foreign gene into a recipient cell by genetic engineering for proliferation and expression. A certain target gene fragment is recombined into a plasmid to constitute a recombinant gene or a recombinant. This recombinant is then transformed into recipient cells (such as E. coli) through microbiological transformation technology, so that the target gene in the recombinant can be propagated or expressed in the recipient bacteria, thereby changing the original characteristics of the host cell. Or create new substances.