Question

Write the types of restriction enzyme. "Synthesis of recominant DNA molecule is possible only when the vectors and source DNA is cut by the same restriction enzyme" explain reason.

Answer 1

Restriction endonucleases are a class of enzyme that cut DNA molecules. Restriction enzymes belong to a larger class of enzymes called nucleases. These are of two kinds:
I. Exonucleases remove nucleotides from the ends of the DNA.
II. Endonucleases make cuts at specific positions within the DNA.
There are four classes of restriction endonucleases:
Types I, II,III and IV.

All types of enzymes recognize specific short DNA sequences and carry out the endonucleolytic cleavage of DNA to give specific double-stranded fragments with terminal 5'-phosphates. They differ in their recognition sequence, sub unit composition, cleavage position, and cofactor requirements.

"Synthesis of recombinant DNA molecule is possible only when the vector and source DNA is cut by the same restriction enzyme"

Explanation:
Restriction enzymes cut the strand of DNA a little away from the centre of the palindrome sites, but between the same two bases on the opposite strands. This leaves single stranded portions at the ends. Them are overhanging stretches called sticky ends on each strand. These are named so because they form hydrogen bonds with their complementary cut counterparts. This stickiness of the ends facilitates the action of the enzyme DNA ligase. Restriction endonucleases are used in genetic engineering to form 'recombinant' molecules of DNA, which are composed of DNA from different sources/genomes. When cut by the same restriction enzyme, the resultant DNA fragments have the same kind of 'sticky-ends' and, these can be joined together (end-to-end) using DNA ligases. Normally, unless one cuts the vector and the source DNA with the same restriction enzyme, the recombinant vector molecule cannot be created.