Recombinant-DNA

1. Introduction to Recombinant DNA (rDNA)

Definition: rDNA refers to DNA formed through laboratory methods of genetic recombination, which combines genetic material from multiple sources to create new sequences.
Chemical Structure: DNA from all organisms has the same structure; differences lie in nucleotide sequences.

General Name: Refers to a DNA piece formed by combining at least two strands; often called chimeric DNA due to combining materials from different species.
Construction Methods:
- Palindromic Sequences: Used in rDNA technology to produce sticky and blunt ends for manipulation.

Purpose: Isolate and clone a single gene or DNA segment into many identical copies, introducing these rDNA molecules into host cells where they can propagate.

Step 1: Isolate the DNA fragment containing the target gene (insert).
Step 2: Cut the DNA using restriction enzymes.
Step 3: Join DNA fragments.
Step 4: Use a vector to insert the DNA fragments into host cells.
Step 5: rDNA molecules are generated as the vector self-replicates in the host cell.
Step 6: Transfer rDNA into appropriate host cells.
Step 7: Select host cells containing rDNA using markers.
Step 8: Replicate selected cells to obtain genetically identical clones.

Donor and Vector DNA Isolation: Purification methods vary based on vector nature; bacterial plasmids are commonly used vectors.
Ultracentrifugation: Plasmids form distinct bands after centrifugation in a cesium chloride gradient, allowing for extraction.
Alkaline Lysis Method: Exploits pH differences to precipitate genomic DNA while keeping plasmids in solution.

Restriction Enzymes: e.g., EcoRI cuts circular DNA to create linear molecules with single-stranded sticky ends for ligation.

Vectors: Any DNA capable of multiplying in hosts can be used (e.g., plasmids).
- Role of Enzymes:
  - Restriction enzymes cut the DNA molecule;
  - Ligase enzymes join vector DNA with gene of interest.

Plasmid Vectors:
- Culture E. coli with the vector, adding calcium ions and heat shock to facilitate DNA entry.
Phage Vectors: Introduced through infection on agar plates to infect bacterial lawns.

Centrifugation: Separates plasmid DNA based on size and density, enabling purification before cutting with restriction enzymes.

Steps:
- Isolate insulin DNA and plasmid from E. coli; using restriction enzymes, cut plasmid, leaving sticky ends.
- Add the insulin gene to the plasmid and ligate.
- Insert the modified plasmid back into E. coli, which will divide and produce human insulin.
- Extract insulin from bacterial cultures.

Gene Mapping: Preparation of gene maps and identification of genes.
Disease Research: Revealing information about infections and genetic disorders.
Genetic Correction: Replacement or correction of defects via gene therapy.
GMOs: Production of transgenic organisms for various nutrients or products.

Negative Features: Potential for ecological imbalances, genetic destruction of plant germplasm, and risks associated with microbial warfare and production of toxic chemicals.