Kerala PSC HSST Botany 2012 Examination
Botany Higher Secondary School Teacher: Junior & Senior
Question Paper Code 40/2012 (Cat. NO. 449/2010)
Original question paper of Kerala PSC HSST Botany Junior / Senior (Higher Secondary School Teacher Botany), Category No. 449/2010) examination conducted by Kerala PSC (Public Service Commission) on 13/04/2002 (Q. Code 40/2012) for the appointment of HSST Botany in Government Higher Secondary Schools of Kerala under the Directorate of Higher Secondary Education, Trivandrum, Govt. of Kerala. Questions are in MCQ (Multiple Choice Questions) format.
Part – 1 (Questions 1 – 25)
(1). Key enzyme in PCR:
a. Taq polymerase
c. Restriction endonuclease
Ans. (a). Taq polymerase
Taq DNA polymerase is a thermostable DNA polymerase enzyme obtained from a thermophilic bacterium Thermus aquaticus. Taq DNA polymerase is frequently used polymerase enzyme in Polymerase Chain Reaction (PCR). The optimum temperature for Taq DNA polymerase is 72oC. Taq DNA polymerase does not have the 3’ – 5’ exonuclease proof reading activity and thus the fidelity of this enzyme is relatively low. Taq DNA polymerase adds a 3’ ‘A’ (adenine) overhang at the 3’ end of PCR products. This property can be used in the ‘TA’ cloning procedure where the PCR products can be easily ligated (cloned) to a vector containing ‘T’ overhangs.
Pfu polymerase is another thermostable DNA polymerase used in PCR, isolated from the bacterium Pyrococcus furiosus. The advantage of using Pfu polymerase over Taq polymerase is that, Pfu polymerase enzyme processes the 3’ – 5’ exonuclease proof reading activity and hence this enzyme shows high fidelity.
EcoRI: restriction enzymes obtained from E. coli.
Restriction enzyme: also called as molecular scissors, are endonuclease enzymes with cut DNA on specific sites, they are important tool in genetic engineering.
Ligase: a class of enzyme which joins two molecules by the formation of new covalent bonds between the two molecules with energy obtained from ATP cleavage. DNA ligase is a type of ligase which catalyzes the formation of phosphodiester bond between two nucleotides.