Explain the following terms in the context of Biotechnology:
$(a)$ $PCR$
$(b)$ Restriction enzymes and $DNA$
$(c)$ Chitinase

(N/A) $PCR$ - Polymerase Chain Reaction (in vitro method) is a molecular biological technique for the enzymatic amplification of a single small strand or a few copies of a segment of $DNA$ into millions of copies of that specific $DNA$ sequence in a short time period (approx $2$ hours).
$3$ steps in $PCR$ are:
$(i)$ Denaturation (at $96\,^{\circ}C$): Separation of desired double-stranded $DNA$ into single-stranded $DNA$ $(ssDNA)$.
$(ii)$ Annealing (at $55-65\,^{\circ}C$): Binding of primers to the $ssDNA$ template.
$(iii)$ Extension (at $72\,^{\circ}C$): Synthesis of new $DNA$ strands by Taq $DNA$ polymerase,isolated from the bacterium $Thermus$ $aquaticus$.
Uses: Amplification of a desired gene or gene cloning.
$(b)$ Restriction enzymes and $DNA$ - Restriction enzymes are a group of enzymes used to cleave or cut $DNA$ strands. Each enzyme recognizes a specific characteristic base sequence known as a recognition site or restriction site.
$(i)$ They restrict foreign $DNA$ from entering a cell by digesting it at specific recognition sites. These sites are typically palindromic.
$(ii)$ They include both endonuclease and exonuclease types.
$(iii)$ They often produce sticky ends. Restriction enzymes are believed to be a defense mechanism evolved by bacteria to resist viral attacks.
$(c)$ Chitinase - Chitinase is a hydrolytic enzyme that digests or breaks down glycosidic bonds in chitin. It is used to break down the cell walls of fungal cells to facilitate the extraction of $DNA$ or other cellular components.