Processes of Recombinant DNA Technology — Revision Notes

⚡ 30-Second Revision

Isolation: — Lysis (lysozyme, cellulase, chitinase), remove RNA (RNase), proteins (protease), precipitate DNA (chilled ethanol).
Cutting: — Restriction endonucleases (molecular scissors) cut at palindromic sites, creating sticky/blunt ends. Separate fragments via Agarose Gel Electrophoresis.
Amplification (PCR): — Denaturation ($94^circ C$), Annealing ($50-65^circ C$), Extension ($72^circ C$) by Taq polymerase. Requires template, primers, dNTPs.
Ligation: — DNA ligase 'glues' foreign DNA into vector.
Insertion: — Transformation ($CaCl_2$ + heat shock for bacteria), Microinjection (animal), Biolistics (plant).
Selection: — Selectable markers (antibiotic resistance), Insertional Inactivation (blue-white screening).
Expression: — Optimal conditions in bioreactors.
Downstream Processing: — Separation, purification, formulation.

2-Minute Revision

Recombinant DNA Technology (RDT) involves a precise sequence of steps to manipulate genetic material. It starts with isolating DNA from donor and vector, using enzymes like lysozyme, cellulase, or chitinase for cell lysis, followed by RNase and proteases to remove contaminants, and finally precipitating DNA with chilled ethanol.

The isolated DNA is then cut into specific fragments using restriction endonucleases, which recognize palindromic sequences and create sticky or blunt ends. These fragments are separated by size using agarose gel electrophoresis.

If the gene is scarce, it's amplified via PCR, a cyclic process of denaturation, annealing (with primers), and extension (by Taq polymerase). The desired gene is then ligated into a vector (e.

g., plasmid) using DNA ligase, forming recombinant DNA. This rDNA is introduced into competent host cells through methods like transformation (bacteria), microinjection (animals), or biolistics (plants).

Selection of successful recombinants is crucial, often using selectable markers (antibiotic resistance) or reporter genes (e.g., blue-white screening for insertional inactivation). Finally, the host cells are cultured to express the foreign gene product, which undergoes downstream processing for purification and formulation.

5-Minute Revision

Recombinant DNA Technology (RDT) is a core biotechnological process involving several critical steps. The journey begins with the Isolation of the Genetic Material (DNA). This requires breaking open cells (lysis) using specific enzymes like lysozyme (bacteria), cellulase (plants), or chitinase (fungi), followed by removing RNA with RNase and proteins with proteases.

The pure DNA is then precipitated using chilled ethanol. The next crucial step is Cutting of DNA at Specific Locations using restriction endonucleases. These 'molecular scissors' recognize and cleave DNA at specific palindromic sequences, generating fragments with either 'sticky' (overhanging) or 'blunt' ends.

The desired gene fragment is then separated and purified from other fragments using agarose gel electrophoresis, where DNA migrates based on size. If the gene of interest is in low quantity, it's Amplified using Polymerase Chain Reaction (PCR).

PCR involves three cyclic steps: denaturation (separating DNA strands at $94-96^circ C$), annealing (primers binding at $50-65^circ C$), and extension (Taq polymerase synthesizing new strands at $72^circ C$).

Once amplified, the gene is Ligated into a Vector (e.g., plasmid) using DNA ligase, which forms phosphodiester bonds, creating recombinant DNA (rDNA). This rDNA is then introduced into a Competent Host Cell.

For bacteria, this is typically done via transformation (calcium chloride treatment and heat shock). For animal cells, microinjection is common, while for plant cells, biolistics (gene gun) or *Agrobacterium*-mediated transfer are used.

A critical phase follows: Selection and Screening of Transformed Cells. Vectors carry selectable markers (e.g., antibiotic resistance genes) to identify cells that have taken up the plasmid. To distinguish between non-recombinant and recombinant plasmids, techniques like insertional inactivation (e.

g., blue-white screening, where insertion into the lacZ gene turns colonies white instead of blue) are employed. Finally, the selected recombinant cells are cultured, often in large bioreactors, to Obtain the Foreign Gene Product (protein expression).

The desired protein is then isolated, purified, and formulated through Downstream Processing, ensuring its quality and safety for application. Each step is vital and interconnected, contributing to the successful genetic modification and product generation.

Prelims Revision Notes

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Isolation of Genetic Material:

* Goal: Obtain pure DNA. * Cell Lysis: Break cell wall/membrane. * Bacteria: Lysozyme (digests peptidoglycan). * Plants: Cellulase (digests cellulose). * Fungi: Chitinase (digests chitin). * Removal of Contaminants: * RNA: RNase. * Proteins: Proteases (e.g., proteinase K), phenol-chloroform extraction. * Lipids/Polysaccharides: Separated during extraction. * DNA Precipitation: Chilled ethanol/isopropanol (DNA is insoluble).

1
Cutting of DNA:

* Enzyme: Restriction endonucleases (molecular scissors). * Recognition Sites: Palindromic sequences (e.g., EcoRI: 5'-GAATTC-3'). * Types of Cuts: Sticky ends (overhangs, preferred for ligation) or blunt ends. * Separation: Agarose Gel Electrophoresis (separates DNA fragments by size; smaller fragments move faster/further). Visualized with Ethidium Bromide under UV light.

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Amplification (PCR):

* Goal: Make millions of copies of a specific DNA segment. * Components: DNA template, two primers, dNTPs, Taq polymerase (heat-stable). * Cycles (Thermal Cycling): * Denaturation: $94-96^circ C$ (separates DNA strands). * Annealing: $50-65^circ C$ (primers bind). * Extension: $72^circ C$ (Taq polymerase synthesizes new strands).

1
Ligation and Insertion:

* Ligation: DNA ligase joins foreign DNA into vector (e.g., plasmid) via phosphodiester bonds. * Vector: Cloning vector (ori, selectable marker, MCS). * Competent Host: Cells treated to take up foreign DNA (e.g., $CaCl_2$ + heat shock for bacteria). * Gene Transfer Methods: * Bacteria: Transformation ($CaCl_2$ + heat shock). * Animal cells: Microinjection, Electroporation. * Plant cells: Biolistics (gene gun), *Agrobacterium tumefaciens* (disarmed pathogen).

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Selection and Screening:

* Goal: Identify cells with recombinant DNA. * Selectable Markers: Genes conferring resistance (e.g., ampicillin, tetracycline) to identify transformed cells. * Insertional Inactivation: Foreign gene inserted into a marker/reporter gene (e.

g., lacZ). Inactivates the gene, allowing differentiation. * Blue-White Screening: LacZ gene produces $\beta$-galactosidase, which cleaves X-gal to produce blue color. If foreign DNA inserts into lacZ, it's inactivated.

Result: White colonies = Recombinants; Blue colonies = Non-recombinants.

1
Obtaining Foreign Gene Product:

* Expression: Recombinant host cells produce the desired protein. * Bioreactors: Large vessels for optimal growth and product yield (controlled temp, pH, aeration, agitation).

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Downstream Processing:

* Goal: Isolation, purification, and formulation of the product. * Techniques: Centrifugation, filtration, chromatography (affinity, ion-exchange, gel filtration), electrophoresis. * Final Product: Must meet quality control standards.

Vyyuha Quick Recall

Isolate, Cut, Amplify, Ligate, Insert, Select, Express, Downstream.

Isolate: Get the DNA out.
Cut: Use restriction enzymes.
Amplify: Make copies with PCR.
Ligate: Glue gene into vector.
Insert: Put into host cell.
Select: Find the successful ones.
Express: Make the protein.
Downstream: Purify the product.