Question

Read the following statements and select the correct ones.
(i) Same kind of sticky ends are produced when a $DNA$ has been cut by different restriction enzymes.
(ii) Exonucleases make cuts at specific positions within the $DNA$.
(iii) Hind II was the first restriction endonuclease to be isolated.
(iv) A bacteriophage has the ability to replicate within bacterial cells by integrating its $DNA$ with bacterial $DNA$.
(v) Presence of more than one recognition sites for a enzyme within the vector complicates the gene cloning.

• A. (i), (iii) and (v)
• B. (i) and (iv)
• C. (iii) and (iv)
• D. (ii), (iii) and (iv)

Answer 1

Answer: (C)

When cut by the same restriction enzyme, the resultant $DNA$ fragments have the same kind of 'stickyends' produced, which can be joined together (end-to-end) using $DNA$ ligase. Restriction enzymes are of two kinds - exonucleases and endonucleases. Exonucleases remove nucleotides from the ends of the $DNA$ whereas endonucleases make cuts at specific positions within the $DNA$. Presence of more than one recognition sites within the vector will generate several fragments, which will complicate the gene cloning. Therefore, in order to link the alien $DNA$ (or foreign $DNA$), the vector needs to have very few, preferably single, recognition/cloning sites for the commonly used restriction enzymes.