Question

Arrange the following steps of formation of recombinant DNA in the correct sequence.
I. Complementary sticky ends are produced on the foreign DNA and the plasmid.
II. Foreign DNA and plasmids are mixed together
III. DNA ligase is used to seal the nicks in the sugar–phosphate backbone.
IV. Cut the foreign DNA (containing the DNA fragment of interest) and the plasmid with the same restriction enzyme.

• A. II, IV, III, I
• B. I, IV, II, III
• C. IV, II, I, III
• D. IV, I, II, III

Answer 1

The correct option is D IV, I, II, III

Recombinant DNA is formed by combining genes of interest with carrier DNA molecules called vectors. The vectors act as vehicles for genes of interest which when introduced into the host cell can make copies of it in the host.

The steps of recombinant DNA technology are:

1. Cut the foreign DNA (containing the DNA fragment of interest) and the plasmid with the same restriction enzyme.

2. If the restriction enzyme makes staggered cuts in the DNA, then complementary sticky ends (ends with single-stranded DNA overhangs) are produced on the foreign DNA and the plasmid.

3. When foreign DNA and plasmids are mixed together, the foreign DNA fragments will pair with the cut ends of the plasmids.

4. DNA ligase is used to seal the nicks in the sugar–phosphate backbone, creating a recombinant plasmid that contains the foreign DNA fragment.

Hence the correct sequence of steps of formation of recombinant DNA is IV, I, II, III.