Question

Explain briefly the procedures of the following techniques used in recombinant DNA Technology:
(i) Transfection
(ii) Electroporation
(iii) Biolistics

Hint:

Biolistics is highly effective for micronutrient-dense or monocotyledonous crops (like rice and maize) and organelles (chloroplasts and mitochondria) that are resistant to Agrobacterium-mediated or chemical transformation methods.

Answer 1

Step 1: (i) Transfection
- Definition: Transfection is the process of deliberately introducing foreign nucleic acids (DNA or RNA) into eukaryotic host cells, particularly animal or mammalian cells.
- Procedure: 1. Chemical-mediated (Lipofection): The target DNA is mixed with cationic liposomes, which spontaneously bind the DNA to form stable lipoplexes.
2. Delivery: These liposomes interact with the negatively charged eukaryotic cell membrane, allowing them to fuse with the membrane or undergo endocytosis.
3. Release: The DNA is released into the cytoplasm, where it migrates to the nucleus for expression.


Step 2: (ii) Electroporation
- Definition: Electroporation is a physical gene transfer method that uses short, high-voltage electrical pulses to introduce DNA into host cells (bacteria, plant, or animal cells).
- Procedure:
1. Preparation: Host cells and recombinant DNA are mixed together in a conductive buffer solution inside a cuvette.
2. Pulse Application: The cuvette is placed in an electroporator, which delivers short, high-intensity electrical pulses.
3. Pore Formation: The electric field destabilizes the phospholipid bilayer, creating temporary micro-pores in the cell membrane.
4. Uptake: Negatively charged DNA molecules migrate through these pores into the cytoplasm. Once the pulse ends, the membrane naturally reseals.


Step 3: (iii) Biolistics (Gene Gun)
- Definition: Biolistics is a mechanical gene transfer method that uses high-velocity microprojectiles to deliver DNA directly into target cells, widely used for plant cells.
- Procedure:
1. Microprojectile Coating: Microscopic heavy metal particles (usually gold or tungsten, $1-2\ \mu\text{m}$ in size) are coated with the recombinant DNA.
2. Acceleration: These coated particles are loaded onto a macrocarrier inside a biolistic "gene gun" and accelerated to high velocities using pressurized helium gas or gunpowder.
3. Penetration: The particles are fired at target tissues. They easily penetrate the rigid cell wall and membrane, releasing the DNA directly into the cell's nucleus.
Final Answer: (i) Transfection uses chemical agents (like liposomes) to deliver DNA into eukaryotic cells. (ii) Electroporation applies electrical pulses to create temporary pores in the cell membrane for DNA uptake. (iii) Biolistics fires DNA-coated heavy metal microprojectiles directly into target plant cells.