Biotechnology Principles and Processes MCQs

Asexual reproduction preserves genetic information [9, II].
Sexual reproduction provides opportunities for variations [9, I].
Genetic engineering allows introduction of only desirable genes, overcoming hybridisation limitations [9, 10, III].
DNA ligase joins cut DNA molecules [14, IV].

Separation and purification are collectively called downstream processing [55, I].
Clinical trials are required for formulations in case of drugs [55, II].
Strict quality control testing is required for each product [55, III].
Formulation involves adding suitable preservatives [55, IV].

The agitator (stirrer) facilitates even mixing and oxygen availability [49, 50, II].
Bioreactors provide optimal growth conditions (Temp, pH, O2) [51, I].
Bioreactors act as vessels converting raw materials into products [51, III].
Stirred-tank reactors are cylindrical or curved at the base to facilitate mixing [49, IV].

Restriction endonucleases cut both strands at specific points in the sugar-phosphate backbones [19, IV].
Nucleases are the larger class of enzymes [18, I].
Exonucleases remove nucleotides from the ends of DNA [18, II].
Endonucleases make cuts at specific positions within the DNA [18, III].

A selectable marker identifies and eliminates non-transformants [28, II].
Non-transformants (lacking the resistance gene) will die on antibiotic medium [46, I].
Transformants (containing the resistance gene) will grow on antibiotic medium [46, IV].
Differential selection using two antibiotics is needed when one gene is inactivated due to insertion [30, 31, III].

A is True: Endonucleases make cuts at specific positions within the DNA double helix by inspecting the DNA length and cutting at specific points in the sugar-phosphate backbone.
R is True: This specificity is achieved because each restriction endonuclease recognizes a specific palindromic nucleotide sequence. R correctly explains A.

A is True: Antibiotic resistance genes are commonly used selectable markers for E. coli because normal cells lack this resistance.
R is True: This statement defines the primary function of a selectable marker. However, R is a definition of the general function, not the specific reason why *ampicillin* resistance genes were chosen or why they function as markers in *E. coli* (i.e., that normal E. coli does not possess resistance). Thus, R is not the correct explanation of A.

A is True: Bacteria are treated with divalent cations (like calcium) to make them competent to take up DNA.
R is True: DNA is hydrophilic, which is why it cannot easily pass through the cell membrane, necessitating the competency treatment. R provides the chemical justification for the requirement stated in A.

A is True: Retroviruses in animals have the ability to transform cells, and scientists have disarmed them to use them as vectors for delivering genes into animal cells.
R is False: Agrobacterium tumifaciens is a pathogen of several *dicot plants*. Its Ti plasmid is generally used for gene delivery into *plant cells*, not animal cells. Moreover, the original Ti plasmid causes tumors, meaning it is not naturally non-pathogenic, though it has been modified to be non-pathogenic for vector use.

A is False: PCR involves repeating cycles including denaturation at high temperatures, which would destroy ordinary DNA polymerase. It requires a thermostable enzyme, and the temperature is not maintained at 37°C throughout.
R is True: A thermostable DNA polymerase (from Thermus aquaticus) is necessary because it resists inactivation during the high temperature denaturation step, allowing repeated amplification.