If a desired gene is identified in an organism for some experiments, explain the process of the following

 If a desired gene is identified in an organism for some experiments, explain the process of the following :

(a) Cutting of desired gene at specific locations.

(b) Synthesis of multiple copies of the desired gene.

Answer.  (a) Desirable DNA sequences are cut by the use of enzyme restriction endonuclease. The restriction enzymes cut the strand of DNA a little away from the centre of the

palindromic sites, between the same two bases on the opposite strands, it leaves single stranded portions at the ends. This forms overhanging stretches called sticky ends on
each strand. They are called sticky as they form hydrogen bonds with their complementary cut counterparts. The stickiness of the ends facilitates the action of the enzyme DNA ligase.
(b) The three steps involved in each cycle of PCR are :
(i) Denaturation
(ii) Annealing
(iii) Extension
PCR is based on the principle that a DNA molecule, when subjected to high temperature, splits into two strands due to denaturation. These single stranded DNA molecules are
then converted to original double stranded molecules, in the presence of enzyme DNA polymerase. A double stranded molecule of DNA is duplicated in this way and multiple copies of original DNA sequence can be generated by repeating the process several times. Such repeated amplification is achieved by the use of thermostable DNA polymerase (isolated from Thermus aquaticus), which remain active during the high
temperature induced denaturation of double stranded DNA.