Question

Read the following statements and select the correct ones.

(i) The same kind of sticky ends are produced when 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 can replicate within bacterial cells by integrating its DNA with bacterial DNA.

(v) The presence of more than one recognition site for an 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)

(iii) and (iv)

• When cut by the same restriction enzyme, the resultant DNA fragments have the same kind of 'sticky-ends' 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.
• The presence of more than one recognition site within the vector will generate several fragments, which will complicate gene cloning. Therefore, 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.