Question

Gene manipulation is a fast emerging science. It started with the development of recombinant DNA molecules. This technology which mostly involves cutting and pasting of desired DNA fragments is based on two most important discoveries in bacteria - presence of plasmid and restriction endonucleases. The science of r-DNA technology took birth when Cohen and Boyer (1973) were able to produce a piece of gene containing foreign DNA introduced into plasmid of E.coli.

(b) What is a plasmid ? Mention its importance in biotechnology.

Hint:

A plasmid is circular extra-chromosomal DNA of bacteria that can replicate on its own. It serves as a cloning vector.

Answer 1

Step 1: Define a plasmid:
A plasmid is a small, circular, double-stranded DNA molecule found in bacteria in addition to the main chromosome.
It is extra-chromosomal and replicates on its own, independent of the chromosomal DNA.

Step 2: Importance in biotechnology:
Plasmids are used as cloning vectors. A foreign gene is inserted into the plasmid and carried into a host cell.
A plasmid has an origin of replication (ori), so it makes many copies of the inserted gene inside the host.

Step 3: More points:
Plasmids carry selectable markers such as antibiotic resistance genes. These help in finding the cells that took up the plasmid.
Plasmids such as pBR322 are also engineered with recognition sites for restriction enzymes.

Final Answer:
A plasmid is an extra-chromosomal, self-replicating circular DNA of bacteria. It is used as a cloning vector to carry and multiply foreign genes.