Read the following passage and answer the questions that follow :
We know that plasmids and bacteriophages are the most commonly used vectors in biotechnology experiments. If we can link an alien piece of DNA to the plasmid DNA, the alien DNA can be multiplied equal to the copy number of the plasmid. Engineered vectors are used these days. Study the diagram of the E. coli cloning vector pBR322 and answer the questions that follow :
(a) Why are plasmids and bacteriophages used as cloning vectors ?
Show Hint
Both can replicate independently in a host cell and give a high copy number of the alien DNA joined to them.
Step 1: Understand the question:
A cloning vector is a DNA molecule that carries an alien DNA piece into a host cell and multiplies it there. We need the reasons plasmids and bacteriophages suit this job.
Step 2: Plasmids:
Plasmids are small circular DNA molecules found in bacteria, separate from the main chromosome.
They have their own origin of replication (ori), so they copy themselves inside the host independently of the chromosome.
Many plasmids are present in a cell in several copies, so the linked alien DNA is multiplied to the same copy number.
Step 3: Bacteriophages:
Bacteriophages are viruses that infect bacteria. Once inside, they multiply very fast and make a large number of copies of their genome.
So an alien DNA joined to phage DNA is also made in very high numbers.
Step 4: Put the points together:
Both can replicate on their own in the host, both give a high copy number, and both can be cut and joined with the alien DNA by enzymes.
Final Answer:
Plasmids and bacteriophages replicate independently inside the host and reach a high copy number, so the alien DNA linked to them is multiplied.
