Question

If a plasmid vector is digested with EcoRl at a single site, then
A) One sticky end will be produced
B) Two sticky ends will be produced
C) Four sticky ends will be produced
D) Six sticky ends will be produced

Answer 1

Hint: Plasmid vectors are double stranded circular DNA. They have restriction sites which can be identified by restriction enzymes like EcoRl.

Complete Answer:
- Restriction endonucleases are known as the molecular scissors.
- They are capable of recognising and cleaving a particular DNA sequence. These enzymes are found in bacteria. Plasmids are the vectors which are a circular DNA molecule.
- They have restriction sites in them which can be recognised by the restriction enzymes.
- Plasmids play an important role in recombinant DNA technology. In RDT, the desired site in the circular DNA is cleaved by using restriction enzymes. This results in producing sticky ends. Then the gene to be inserted in the clone is ligated by the help of ligase enzymes.
When a plasmid vector is cut by EcoR1, it results in sticky ends.
- Sticky ends contain certain sequences of nucleotides. EcoR1 produces sticky ends with AATT nucleotide chain.

Thus the correct answer is B. Two sticky ends are produced when EcoR1 cuts the plasmid at one recognition site.

Note: EcoR1 is the restriction enzyme isolated from E.coli. The EcoR1 recognition site is GAATTC. It cleaves the DNA at a single restriction site resulting in sticky ends.