Question

Select the correct methods to introduce the recombinant DNA into the host cells.
(A) Biolistics or gene gun for plant cells
(B) Micro-injection for an animal cell
(C) 'Disarmed pathogen' vectors
(D) By heating the host cell at $100^\circ\text{C}$ and then cooling to $70^\circ\text{C}$
Choose the correct answer from the options given below:

• A. (A), (B) and (C) only
• B. (B) and (D) only
• C. (B), (C) and (D) only
• D. (A) and (C) only

Hint:

Transformation Techniques:
$\bullet$ Gene gun Biolistics: Plant cells (Gold/Tungsten microparticles).
$\bullet$ Micro-injection: Animal cells (Direct injection into nucleus).
$\bullet$ Heat Shock: $Ca^{2+}$ treated bacteria placed on ice, then $42^\circ\text{C}$, then back to ice.

Answer 1

The Correct Option is A

Concept:
Since DNA is a hydrophilic molecule, it cannot pass directly across lipid cellular membranes. Recombinant biotechnology employs physical, chemical, and biological methods to introduce recombinant DNA into competent host cells.

Step 1: Evaluating Gene Transfer Methods:
- Statement (A): Biolistics or gene gun is a direct physical transformation method suitable for plant cells, where cells are bombarded with high-velocity microscopic gold or tungsten particles coated with recombinant DNA. This statement is correct.
- Statement (B): Micro-injection is a direct method used for animal cells, where recombinant DNA is injected directly into the nucleus using a glass micropipette. This statement is correct.
- Statement (C): Disarmed pathogen vectors (e.g., disarmed Ti-plasmid of Agrobacterium for plants, and disarmed retroviruses for animals) transfer foreign genes upon infecting host cells without causing disease. This statement is correct.
- Statement (D): Chemical transformation of bacterial cells using divalent cations ($Ca^{2+}$) involves heat shock at $42^\circ\text{C}$ followed by rapid cooling on ice ($0^\circ\text{C}$). Heating cells to $100^\circ\text{C}$ would denature proteins, melt cellular membranes, and kill the host cells. Thus, (D) is incorrect.

Step 2: Conclusion:
Statements (A), (B), and (C) are correct.
Hence, Option (A) is the correct choice.