CBSE 12 Chapter 9 Biology : Biotechnology Principles and Processes

Biotechnology is defined by the European Federation of Biotechnology (EFB) as the integration of natural science and organisms, cells, or molecular analogues for products and services. It primarily encompasses two core techniques: Genetic Engineering, which involves altering the chemistry of DNA/RNA to change the host's phenotype, and Bioprocess Engineering, which maintains sterile environments for the mass production of antibiotics, vaccines, and enzymes. Unlike traditional hybridization, which often multiplies undesirable genes, recombinant DNA (rDNA) technology allows for the isolation and introduction of only specific desirable genes into a target organism.

I. Core Principles of Biotechnology

• Genetic Engineering: Techniques to create recombinant DNA, use gene cloning, and perform gene transfer to isolate and introduce specific genes.
• Bioprocess Engineering: Maintenance of a contamination-free environment in chemical engineering processes to grow only the desired microbe or eukaryotic cell in large quantities.

II. Key Tools of Recombinant DNA Technology

To accomplish genetic engineering, several key tools are required: Restriction Enzymes, Polymerase Enzymes, Ligases, Vectors, and a Host Organism.

1. Restriction Enzymes (Molecular Scissors)

• Function: They identify and cut DNA at specific palindromic nucleotide sequences.
• Naming Convention: The first letter is from the genus, and the next two are from the species (e.g., EcoRI comes from Escherichia coli RY 13).
• Sticky Ends: Many restriction enzymes leave overhanging, single-stranded portions called sticky ends which form hydrogen bonds with complementary cut counterparts, facilitating the action of DNA ligase.

Comparison: Exonucleases vs. Endonucleases

2. Cloning Vectors

Vectors act as "vehicles" to deliver alien DNA into a host organism; common examples include plasmids and bacteriophages.

Key Features of a Vector:

• Origin of Replication (ori): A specific DNA sequence where replication starts; it also controls the copy number of the linked DNA.
• Selectable Marker: Helps identify and eliminate non-transformants while permitting the growth of transformants (e.g., genes for resistance to ampicillin or tetracycline).
• Cloning Sites: Specific locations where the alien DNA is linked; vectors should ideally have a single recognition site for a restriction enzyme to avoid fragmenting the vector.

Diagrammatic Representation of pBR322 (E. coli cloning vector):

• Resistance Genes: ampR (ampicillin) and tetR (tetracycline).
• Restriction Sites: BamHI and SalI (within tetR); PstI and PvuI (within ampR); EcoRI, ClaI, HindIII.
• Other Features: ori (origin of replication) and rop (codes for proteins involved in plasmid replication).

III. Processes of Recombinant DNA Technology

1. Isolation of Genetic Material (DNA)

• Cells are broken open using enzymes: Lysozyme (bacteria), Cellulase (plants), or Chitinase (fungi).
• RNA is removed by ribonuclease, and proteins are removed by protease.
• Purified DNA is precipitated by adding chilled ethanol, appearing as fine threads.

2. Amplification using PCR (Polymerase Chain Reaction)

PCR is used to synthesize billions of copies of a DNA segment in vitro.

• Step 1: Denaturation: Double-stranded DNA is separated into single strands by high temperature.
• Step 2: Annealing: Two sets of primers (small oligonucleotides) bind to the complementary regions.
• Step 3: Extension: Taq polymerase (a thermostable DNA polymerase from Thermus aquaticus) extends the primers using nucleotides.

3. Insertion of rDNA into Host (Competent Host)

• Chemical Method: Treating cells with divalent cations (like calcium) followed by heat shock (alternating ice and 42°C).
• Micro-injection: DNA is injected directly into the nucleus of an animal cell.
• Biolistics/Gene Gun: Cells are bombarded with high-velocity gold or tungsten micro-particles coated with DNA (suitable for plants).
• Disarmed Pathogens: Using modified viruses or bacteria (like Agrobacterium tumifaciens or retroviruses) to infect and transfer DNA.

4. Obtaining the Foreign Gene Product

• Bioreactors: Large vessels (100–1000 liters) that provide optimal growth conditions (pH, temperature, oxygen) for producing desired proteins on a large scale.
• Downstream Processing: A series of processes involving separation and purification of the product before it is formulated and clinically tested.

Frequently Asked Questions (FAQs)

1. Why are "sticky ends" important in genetic engineering?
   
   Sticky ends are single-stranded overhanging DNA stretches that facilitate the joining of DNA fragments from different sources. They form hydrogen bonds with their complementary counterparts, allowing the enzyme DNA ligase to easily bond the segments together into a recombinant molecule.
   
   
2. What is the role of a "selectable marker" in a cloning vector?
   
   A selectable marker allows researchers to distinguish between transformants (cells that took up the rDNA) and non-transformants. Common markers include antibiotic resistance genes or genes like β-galactosidase, which use insertional inactivation to produce color-coded results.
   
   
3. Why is a thermostable DNA polymerase (Taq polymerase) used in PCR?
   
   PCR requires high temperatures to denature DNA strands, which would normally destroy standard polymerase enzymes. Taq polymerase, isolated from the bacterium Thermus aquaticus, remains active at high temperatures, enabling the repeated cycles of DNA amplification.