Explain the importance of
(a) restriction endonuclease,
(b) "Ori" and
(c) gel-electrophoresis in recombinant DNA technology. (3 marks)
(a) Restriction endonuclease. It cuts the two strands of DNA at specific points in their sugar phos-
phates back bone, a little away from the centre of the palindrome sites, but between the same
two bases on both the strands. As a result single-stranded portion called sticky ends, are pro-
duced at the ends of the DNA. This stickiness of the ends facilitates the action of enzyme DNA
ligase. Exmaple :
(b) Ori : This is a sequence from where replication begins and any piece of DNA linked to this
sequence can be made to replicate within the host cells. This sequence is also responsible for
controlling the copy number of the linked DNA. If one wants more number of alien DNA then it
should be cloned in a vector, whose origin supports high copy number.
(c) Gel-electrophoresis : Fragments of DNA can be separated by a technique known as gel-electro-
phoresis. The DNA fragments purified by this method can be used in constructing recombinant
DNA by joining them with cloning vectors.