Recombinant Dna Technology And Applications

Ampicillin resistance gene: This gene encodes a protein that makes the bacteria resistant to the antibiotic ampicillin, and hence gives the bacteria a selective advantage in the presence of ampicillin. Lac Z gene: The Lac Z gene encodes an enzyme called beta-galactosidase which is required for breaking down the disaccharide lactose. GFP gene: The GFP (Green Fluorescent Protein) gene encodes a protein that fluoresces green under UV light. Tetracycline resistance gene: This provides resistance against the antibiotic tetracycline. Leu 2 gene: This is a marker gene which codes for an enzyme needed for synthesis of an amino acid, leucine.

The construction of a recombinant DNA molecule generally involves the following steps: Isolation of DNA: The first step is to isolate the desired DNA fragment from a source (such as genomic DNA) and also the vector DNA (usually a plasmid) that will carry the desired DNA sequence into a host organism. Cutting the DNA: Both the target DNA fragment and the vector DNA are then cut using the same restriction enzyme. This enzyme will create “sticky ends" or specific sequence on the DNA that can be used to join the target and the vector DNA. Ligation: Next, the target and vector DNAs are joined together using a DNA ligase. This enzyme facilitates the formation of phosphodiester bonds, which joins the DNA sequences together, resulting in a recombinant DNA molecule, also known as a ‘chimeric’ DNA. Transformation: This new molecule (vector plus insert) is then introduced into a host organism like E.coli} through the process called transformation. Here the bacteria can grow, and it will replicate the vector containing the insert DNA. Selection and Screening: The transformed cells are then screened to verify whether the DNA fragment has been successfully inserted. This usually involves antibiotic resistance and other selection techniques.

M13: M13 is a bacteriophage (a virus that infects bacteria) known for infecting E. coli cells containing an F-plasmid, and it has a single-stranded circular genome. This single stranded nature is very useful in many biological and biotechnological procedures. Agrobacterium tumefaciens: Agrobacterium tumefaciens is a bacterium used to transfer genes in plant cells. YEp: YEp is a yeast episomal plasmid and not related to E. coli. pBR322: pBR322 is a commonly used plasmid vector and not a virus, that is used in bacteria.

Recombinant DNA Technology involves combining DNA molecules from different sources to create new genetic combinations. The basic steps are:

1. Isolation of DNA: Extract the gene of interest from the donor organism and the vector DNA (usually a plasmid).
2. Cutting DNA: Use restriction enzymes (restriction endonucleases) to cut both the gene and the vector DNA at specific sequences, creating compatible ends.
3. Ligation: Join the gene and vector DNA fragments using the enzyme DNA ligase to form a recombinant DNA molecule.
4. Transformation: Introduce the recombinant DNA into a suitable host cell (like E. coli) by transformation.
5. Selection: Grow the host cells on selective media to identify cells that have taken up the recombinant DNA.
6. Screening: Confirm the presence and expression of the inserted gene in transformed cells.

This technology allows production of genetically modified organisms, therapeutic proteins, and vaccines.

The Blue-White selection method is used to identify bacterial cells that have taken up recombinant plasmids containing the gene of interest. Principle: This technique relies on the disruption of the lacZ gene that encodes the enzyme β-galactosidase. The plasmid contains a multiple cloning site within the lacZ gene. When a foreign DNA fragment is inserted into this site, it disrupts lacZ function. Procedure:

• Bacterial cells are transformed with plasmids and grown on agar plates containing the antibiotic (to select for plasmid uptake) and X-gal, a chromogenic substrate for -galactosidase.
• If the plasmid does not contain an insert (non-recombinant), -galactosidase is active and cleaves X-gal, producing blue colonies.
• If the plasmid contains the insert disrupting lacZ (recombinant plasmid), -galactosidase is inactive, and colonies remain white.

Result:

• Blue colonies: Non-recombinant cells without the gene of interest.
• White colonies: Recombinant cells containing the desired gene insert.

This method allows easy visual screening of recombinant bacterial colonies.

The isolation of recombinant insulin (Humulin) from Escherichia coli involves the following key steps:

1. Gene Cloning: The human insulin gene is inserted into a suitable plasmid vector.
2. Transformation: The recombinant plasmid is introduced into E. coli cells.
3. Expression: Transformed E. coli are cultured to express the insulin protein.
4. Harvesting: Bacterial cells are collected after sufficient growth.
5. Cell Lysis: Cells are broken open to release the insulin protein.
6. Purification: Insulin protein is purified using techniques such as chromatography to remove bacterial contaminants.
7. Folding and Processing: The purified insulin is refolded to its active form if expressed as inactive precursors.
8. Formulation: The final insulin product is formulated for medical use.

These steps ensure safe, large-scale production of human insulin for diabetic patients.

DNA ligase is a key enzyme used in recombinant DNA technology for joining DNA fragments by forming phosphodiester bonds. The enzyme most widely used in labs is derived from the T4 bacteriophage.

• T4 Bacteriophage: Produces T4 DNA ligase, which is highly effective in joining both sticky and blunt ends of DNA fragments. It is the standard enzyme used in genetic engineering for constructing recombinant DNA molecules.
• T2 Bacteriophage: Though similar in nature, it is not the source of the commonly used DNA ligase.
• Lambda Bacteriophage: Used as a cloning vector in molecular biology, but not the source of DNA ligase.
• M13 Filamentous Phage: Important in sequencing and cloning vectors but does not provide the ligase enzyme.

Thus, the correct and most suitable answer is (B) T4 Bacteriophage.