Question

1. Describe how a plasmid can be modified to include a piece of foreign DNA.

Answer 1

Plasmids are circular piece of DNA other than the bacterial DNA. They can replicate independently. This property is used to produce many copies or amplify certain genes.

The steps by which plasmids can be modified to include piece of foreign DNA are :

1. The plasmid is cut at restriction site by a restriction enzyme. Restriction sites are the sites which are recognised by the restriction enzyme. The restriction enzymes, also called the molecular scissors, cuts the plasmid at those recognised sites.

2. The cut ends are called sticky ends. They can bind to their complementary nucleotide. The gene of interest must have the complementary nucleotide sequence.

3. The DNA is taken from cell and gene of interest is identified from the DNA. These are then cut using the same restriction enzymes. Hence both the plasmid and the gene of interest are cut.

4. The gene of interest is properly inserted into its correct orientation and DNA ligases connects the gene of interest with the sticky ends with phosphodiester bonds. This creates a recombinant DNA.

By this way, the plasmids are genetically modified by including a foreign piece of DNA. The process is then followed by transformation in which bacteria takes up the genetically modified plasmids.