Question

How are plasmids classified?

Answer 1

Plasmids:

1. Plasmid is small in size, circular in shape and it is a piece of DNA that is not the same as chromosomal DNA.
2. Its ability to replicate is independent of chromosomal DNA.
3. They are usually found in bacteria, but they are also present in multicellular organisms

Classification of plasmids:

1. Plasmids can be classified on the basis of their ability to transfer to other bacteria.
2. They are classified as non-conjugative and conjugative plasmids.
3. Conjugative plasmids are known to contain transfer (tra) genes which perform the process of conjugation.
4. The conjugative plasmids are distinguished by their ability to facilitate sexual conjugation between bacterial cells.
5. This can cause the conjugative plasmid to spread from one to another cell in a bacterial culture.
6. Plasmid transfer and conjugation are regulated by a set of transfer genes found on conjugative plasmids which are absent in the non-conjugative type.
7. But, in some circumstances, non-conjugative plasmids may be transferred along with a conjugative plasmid when both are found in the same cell.
8. Generally, non-conjugative plasmids can only be transferred through sexual conjugation with the help of conjugative plasmids.
9. Plasmids are also classified on the basis of specific types these are:

1. Col plasmids: Col plasmids contain genes that make bacteriocins (also known as colicins), which are proteins that kill other bacteria and thus defend the host bacterium.
2. Resistance (R) plasmids: Resistance or R plasmids transfer through conjugation and contain genes that help a bacterial cell defend against environmental factors such as poisons or antibiotics.
3. Fertility (F) plasmids: Fertility plasmids, also known as F-plasmids fall under the broad category of conjugative plasmids and contain transfer genes that allow genes to be transferred from one bacteria to another through conjugation.
4. Virulence (Vir) plasmids: A virulence plasmid turns a host bacterium into a pathogen, which is an agent of disease.
5. Degradative plasmids: Degradative plasmids help the host bacterium to digest compounds that are not commonly found in nature, such as camphor, xylene, toluene, and salicylic acid.