Question

How are ‘sticky ends’ formed on a DNA strand? Why are they so called?

Answer 1

Hint: The technique of cloning used in molecular biology and recombinant technology requires the insertion of DNA into the vector DNA. The inserted DNA has to be generated with the desired sequence so that it can be easily inserted into the vector for proper expression. Such ends of DNA are generated through the use of restriction enzymes.

Complete answer:
Restriction enzymes are the enzymes that cut DNA with distinct cuts at specific places to generate ends of DNA molecules which are known as sticky ends. The restriction enzyme cleaves the DNA into fragments at or near specific recognition sites within the molecules. It cuts the DNA to generate ends which are known as sticky ends. They were discovered as a product of the action of EcoRI by Ronald W.Davis.
A sticky end is generated due to the cuts made by the restriction enzymes at one end of the sequence. The cut is made between the two bases on the same strands and also cuts on the opposite end of the complementary strand. The result is the two ends of DNA which contains some nucleotides without some complementary bases. The digestion of the DNA strand gives rise to overhanging structures.
The sticky ends are also known as the cohesive ends and are mostly formed by the restriction endonucleases enzymes whenever they cut the DNA strands. The sticky ends can be ligated or joined back together by using the enzyme DNA ligase. The DNA ligase enzymes allow the ligation of two sticky ends.
The most important function of the sticky ends and their property of joining back together are useful in the recombinant DNA technology. The sticky ends allow the insertion of foreign DNA into the genome of the host. This process involves the cutting of the plasmid at the same restriction enzymes and producing sticky ends. This property of the sticky strands allows the insertion of required DNA molecules.

Note: The insertion of DNA molecules requires the use of enzymes known as the restriction enzymes which allows cuts on the DNA strands to generate overhanging ends which are known as sticky ends. These ends can be joined back together by using another enzyme, known as the DNA ligase.