Question

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?     [1]

(b) (i) Identify:     [1]

1. The gene in the cloning vector that controls the copy number of the vector.
2. The restriction site - C in the ‘rop’ gene.

OR

(b) (ii) Identify and name two selectable markers shown in the diagram.     [1]

(c) Name the two restriction sites each in the two genes you have identified as selectable markers.     [2]

Answer 1

(a) Because plasmids and bacteriophages can carry foreign (alien) DNA into host cells and replicate independently in the host, producing many copies of the inserted DNA; they are easy to cut/ligate (have useful restriction sites) and contain selectable markers for identifying transformants.

(b) (i)

1. The rop gene.
2. The restriction site labelled C is located in the rop gene (site C on the map).

OR

(b) (ii) ampicillin resistance gene (AmpR) and tetracycline resistance gene (TetR).

(c) The two restriction sites in each selectable-marker gene:

• AmpR (ampicillin resistance) gene: sites A and B.
• TetR (tetracycline resistance) gene: sites D and E.