Question

What are plasmids? How do they differ from the genomic DNA? Where are they located? What are the uses?

Answer 1

Hint: DNA is the genetic material found in bacteria and also humans whereas plasmid is extrachromosomal DNA. It is small, circular and double stranded. They are generally present in some archaea, bacteria and also some eukaryotic organisms.

Complete Answer:
Plasmids are a piece of DNA that are physically separated from the chromosomal DNA. They are found in Bacteria and in certain archaea and multicellular organisms too. Plasmids are circular and double stranded. Plasmids can be conjugative or non conjugative depending on if they can transfer genetic material between 2 bacteria by sexual conjugation or not.

Different types of plasmid:
i. Fertility Plasmids: They are also known as F-plasmids. These are called so because they carry transfer genes which allow the genes to be transferred between 2 bacteria during conjugation. Hence, they are called conjugative plasmids. They are episomes i.e they can be integrated into the chromosomal DNA.
ii. Resistance Plasmids: R plasmids carry resistant genes against certain external factors like antibiotics.
iii. Virulence Plasmids: A plasmid whose presence in a bacterium can make it pathogenic and eventually an infective agent is called a virulence plasmid. These can be easily spread from infected to uninfected people and replicate fast also. For example, E.coli have virulence plasmids.
iv. Degradative Plasmids: Certain plasmids help the host bacterium in breaking down complex compounds found in environments like camphor, toluene, etc. They carry the genes for such degradative enzymes.
v. Col Plasmids: Genes carried by Col plasmids produce Bacteriocins or colicins protein. These are involved in defending the host by killing other bacteria.

Sl.No	Plasmid DNA	Genetic DNA
1.	It is circular DNA.	It can be linear or circular.
2.	It is always double stranded.	It can be double stranded or single stranded.
3.	It is located in the cytoplasm.	It is located in the nucleus of the cell.
4.	It is smaller in size. (1-200 kbp)	Size is comparatively large.
5.	It can be transferred from between the same or different species by conjugation.	It is passed to the same species by cell division.
6.	It replicates independently from the cell.	It replicates with the genome.
7.	It is not associated with histone proteins.	Associated with histone proteins.

Uses of Plasmid DNA:
i. Used as a vector in recombinant DNA technology.
ii. It can be used to make copies of some genes.
iii. Helps in cloning of genes.
iv. Used by scientists in drug discovery

Note: Plasmids are an important tool in genetic engineering and recombinant DNA technology which is self replicating and are highly stable. They are also used in gene therapy for transfer of corrected genes in human cells.