Biotechnology: Principles and Processes (NCERT Class 12)

Definition and Principles of Biotechnology

Biotechnology is defined as the use of living organisms, their enzymes, or biological systems to create products and processes beneficial to humans. While traditional biotechnology includes age-old practices such as bread-making, brewing, and curd preparation using microorganisms, modern biotechnology specifically involves the controlled manipulation of genetic material and large-scale production of biological products.

Modern biotechnology rests on two core principles. The first is genetic engineering, which involves altering the DNA of an organism by inserting, deleting, or modifying specific genes using molecular tools. The second is bioprocess engineering, which deals with maintaining sterile conditions and providing optimal growth environments (such as controlled temperature, pH, and oxygen levels) to grow modified organisms at an industrial scale in devices called bioreactors.

• Biotechnology uses living organisms or their enzymes to make useful products
• Traditional biotechnology includes fermentation-based processes like bread and curd making
• Modern biotechnology involves genetic engineering and bioprocess engineering
• Genetic engineering manipulates DNA using molecular tools like restriction enzymes
• Bioprocess engineering scales up production using bioreactors under controlled conditions

Tools of Recombinant DNA Technology

Recombinant DNA technology requires three essential tools: restriction enzymes, cloning vectors, and a competent host organism. Restriction enzymes (restriction endonucleases) are molecular scissors that cut DNA at specific recognition sequences. These recognition sequences are usually palindromic, meaning the sequence reads the same on both strands in the 5-prime to 3-prime direction. For example, the enzyme EcoRI recognises the six-base-pair sequence GAATTC and cuts between G and A on both strands, producing fragments with single-stranded overhangs called sticky ends. These sticky ends can pair with complementary sticky ends from another DNA molecule, facilitating the joining of DNA from different sources.

Cloning vectors are DNA molecules that carry the foreign gene into the host cell and allow it to replicate. Plasmids are the most commonly used vectors. A good vector must have an origin of replication (ori) so it can replicate independently inside the host, a selectable marker gene (such as antibiotic resistance) to identify cells that have taken up the vector, and unique restriction enzyme sites (a cloning site) where foreign DNA can be inserted. Other vectors include bacteriophages and cosmids. DNA ligase is the enzyme that seals the gap between the inserted gene and the vector DNA by forming phosphodiester bonds.

• Restriction enzymes cut DNA at specific palindromic recognition sequences
• EcoRI recognises GAATTC and produces sticky ends by cutting between G and A
• Sticky ends allow foreign DNA to pair with vector DNA for joining
• Plasmids are circular, self-replicating DNA molecules used as cloning vectors
• A vector needs an origin of replication, a selectable marker, and a cloning site
• DNA ligase joins DNA fragments by forming phosphodiester bonds
• Other vectors include bacteriophages, cosmids, and artificial chromosomes

Processes of Recombinant DNA Technology

Creating recombinant DNA involves a series of steps. First, the genetic material (DNA) is isolated from the source organism. Cells are lysed using enzymes (lysozyme for bacteria, cellulase for plant cells) and detergents. RNA is removed using ribonuclease, and proteins are digested with protease. The purified DNA is then precipitated using chilled ethanol and appears as fine threads that can be collected.

The isolated DNA is cut using a specific restriction enzyme, and the same enzyme is used to cut the vector DNA so that both have compatible sticky ends. The gene of interest is then inserted into the vector using DNA ligase in a process called ligation. The resulting recombinant DNA molecule is introduced into a competent host cell (usually Escherichia coli) through a process called transformation. Host cells are made competent by treatment with calcium chloride, which increases the permeability of the cell membrane to DNA. Alternatively, methods such as micro-injection, biolistics (gene gun), or electroporation can be used to introduce DNA into host cells.

• DNA is isolated by lysing cells and removing RNA and proteins
• Purified DNA is precipitated with chilled ethanol
• Both the gene of interest and the vector are cut with the same restriction enzyme
• DNA ligase joins the gene into the vector, creating recombinant DNA
• Transformation introduces recombinant DNA into competent host cells
• Competent cells are prepared by calcium chloride treatment
• Other methods include micro-injection, biolistics (gene gun), and electroporation

PCR and Selection of Recombinants

The Polymerase Chain Reaction (PCR) is a technique that amplifies a specific segment of DNA in vitro, producing millions of copies from a small starting amount. PCR uses a thermostable DNA polymerase called Taq polymerase, isolated from the bacterium Thermus aquaticus, which can withstand the high temperatures used in the process. Each PCR cycle has three steps: denaturation (heating to about 94 degrees Celsius to separate the two DNA strands), annealing (cooling to about 55 to 65 degrees to allow short DNA primers to bind to the target sequence), and extension (heating to about 72 degrees so Taq polymerase synthesises new strands). Repeated cycling doubles the number of copies each round.

After transformation, not all host cells will contain the recombinant DNA. Selectable markers such as antibiotic resistance genes help identify successful transformants. In insertional inactivation, the foreign gene is inserted into a marker gene (for example, the lacZ gene encoding beta-galactosidase), disrupting its function. Colonies containing recombinant DNA appear white on a medium with a chromogenic substrate (X-gal), while non-recombinant colonies appear blue because their intact lacZ gene produces functional beta-galactosidase. This blue-white screening is a standard method for distinguishing recombinants from non-recombinants.

• PCR amplifies a specific DNA segment using repeated thermal cycles
• Taq polymerase from Thermus aquaticus withstands the high denaturation temperatures
• Three PCR steps per cycle: denaturation (94 C), annealing (55-65 C), extension (72 C)
• Each cycle approximately doubles the number of DNA copies
• Selectable markers like antibiotic resistance identify transformed cells
• Insertional inactivation disrupts a marker gene when foreign DNA is inserted
• Blue-white screening with X-gal distinguishes recombinant (white) from non-recombinant (blue) colonies

Bioreactors and Downstream Processing

Once a recombinant organism is created and confirmed, it must be grown at a large scale to produce the desired protein or product in usable quantities. Bioreactors are large vessels (typically 100 to 1000 litres) that provide the optimal conditions for microbial growth, including controlled temperature, pH, oxygen supply, and nutrient medium. The most commonly used type is the stirred-tank bioreactor, which has a mechanical stirrer (impeller) that mixes the contents and ensures even distribution of oxygen and nutrients. A sparger introduces sterile air into the vessel. Bioreactors also have ports for sampling, inlet and outlet valves, and sensors to monitor conditions in real time.

After the desired product has been produced inside the bioreactor, it must be separated and purified through a series of steps collectively called downstream processing. This includes filtration, centrifugation, chromatography, and other separation techniques. The purified product must then pass quality control tests, and for pharmaceutical products, clinical trials are required before the product can be marketed. Downstream processing can account for a significant portion of the total production cost.

• Bioreactors are large vessels (100 to 1000 litres) for growing modified organisms at scale
• Stirred-tank bioreactors use an impeller for mixing and a sparger for aeration
• Controlled parameters include temperature, pH, oxygen, and nutrient supply
• Downstream processing separates and purifies the product after biosynthesis
• Techniques include filtration, centrifugation, and chromatography
• Pharmaceutical products require clinical trials and quality testing before release
• Downstream processing is a major component of total production cost

Key Terms

Restriction Endonuclease

An enzyme that recognises a specific palindromic DNA sequence and cuts both strands at defined positions, producing fragments with sticky or blunt ends. Used as molecular scissors in recombinant DNA technology.

Plasmid

A small, circular, self-replicating DNA molecule found in bacteria that is separate from the chromosomal DNA. Used as a cloning vector to carry foreign genes into host cells.

Polymerase Chain Reaction (PCR)

An in vitro technique that amplifies a specific DNA segment through repeated cycles of denaturation, primer annealing, and extension using the thermostable enzyme Taq polymerase.

Downstream Processing

The series of separation and purification steps applied after biosynthesis in a bioreactor to obtain the final product in a pure, usable form, including filtration, centrifugation, and chromatography.

Practice Quiz — 20 Questions

1. What is biotechnology?

   • A.The study of living cells under a microscope
   • B.The use of living organisms or their enzymes to create useful products
   • C.The chemical synthesis of drugs in a laboratory
   • D.The study of ecosystems and biodiversity
   B. The use of living organisms or their enzymes to create useful products — Biotechnology is defined as the branch of biology that uses living organisms, their parts, or biological processes to develop products and technologies useful to humankind.

2. What are the two core principles of modern biotechnology?

   • A.Cloning and hybridisation
   • B.Genetic engineering and bioprocess engineering
   • C.Fermentation and pasteurisation
   • D.Cell culture and tissue engineering
   B. Genetic engineering and bioprocess engineering — Modern biotechnology rests on genetic engineering (manipulation of DNA) and bioprocess engineering (large-scale production in bioreactors under controlled conditions).

3. What are restriction endonucleases?

   • A.Enzymes that join DNA fragments
   • B.Enzymes that cut DNA at specific recognition sequences
   • C.Enzymes that replicate DNA
   • D.Enzymes that transcribe DNA to RNA
   B. Enzymes that cut DNA at specific recognition sequences — Restriction endonucleases are molecular scissors that recognise specific palindromic sequences in DNA and cut both strands at defined positions.

4. What type of DNA sequence does a restriction enzyme typically recognise?

   • A.Random sequence
   • B.Palindromic sequence
   • C.Repetitive sequence
   • D.Promoter sequence
   B. Palindromic sequence — Restriction enzymes recognise palindromic sequences, which read the same on both complementary strands in the 5-prime to 3-prime direction.

5. The restriction enzyme EcoRI recognises which sequence?

   • A.AATTCC
   • B.GAATTC
   • C.GGATCC
   • D.AAGCTT
   B. GAATTC — EcoRI recognises the six-base-pair palindromic sequence GAATTC and cuts between G and A on both strands, producing sticky ends.

6. What are sticky ends?

   • A.Blunt-cut DNA fragments
   • B.Single-stranded overhangs produced by staggered cuts in DNA
   • C.Circular DNA molecules
   • D.RNA primers attached to DNA
   B. Single-stranded overhangs produced by staggered cuts in DNA — Sticky ends are single-stranded overhangs produced when a restriction enzyme cuts DNA at staggered positions. They can base-pair with complementary sticky ends from other DNA molecules.

7. Which enzyme joins DNA fragments by forming phosphodiester bonds?

   • A.DNA polymerase
   • B.Restriction endonuclease
   • C.DNA ligase
   • D.Helicase
   C. DNA ligase — DNA ligase seals the gaps between DNA fragments by forming phosphodiester bonds, joining the inserted gene to the vector DNA.

8. What must a cloning vector possess for it to replicate inside a host cell?

   • A.A centromere
   • B.An origin of replication (ori)
   • C.A telomere
   • D.An intron
   B. An origin of replication (ori) — A cloning vector must have an origin of replication (ori) that allows it to replicate independently inside the host cell.

9. What is the purpose of a selectable marker in a vector?

   • A.To cut the foreign DNA
   • B.To identify host cells that have taken up the vector
   • C.To provide nutrients for growth
   • D.To separate DNA strands
   B. To identify host cells that have taken up the vector — Selectable markers, such as antibiotic resistance genes, allow researchers to identify and select host cells that have successfully taken up the vector.

10. Which organism is most commonly used as a host in recombinant DNA technology?

    • A.Saccharomyces cerevisiae
    • B.Bacillus subtilis
    • C.Escherichia coli
    • D.Staphylococcus aureus
    C. Escherichia coli — Escherichia coli (E. coli) is the most commonly used host organism because it is well-studied, grows rapidly, and is easy to manipulate genetically.

11. What chemical is used to make host cells competent for transformation?

    • A.Sodium chloride
    • B.Calcium chloride
    • C.Potassium permanganate
    • D.Magnesium sulphate
    B. Calcium chloride — Host cells are treated with calcium chloride (CaCl2) to increase cell membrane permeability, making them competent to take up foreign DNA.

12. What is the gene gun method also known as?

    • A.Electroporation
    • B.Biolistics
    • C.Micro-injection
    • D.Lipofection
    B. Biolistics — The gene gun method is also called biolistics. It involves bombarding cells with high-velocity micro-particles coated with DNA to introduce foreign genes.

13. From which organism is Taq polymerase obtained?

    • A.Escherichia coli
    • B.Thermus aquaticus
    • C.Agrobacterium tumefaciens
    • D.Bacillus thuringiensis
    B. Thermus aquaticus — Taq polymerase is isolated from Thermus aquaticus, a thermophilic bacterium found in hot springs. It is thermostable and can withstand the high temperatures used in PCR.

14. What are the three steps of each PCR cycle in order?

    • A.Annealing, denaturation, extension
    • B.Denaturation, extension, annealing
    • C.Denaturation, annealing, extension
    • D.Extension, denaturation, annealing
    C. Denaturation, annealing, extension — Each PCR cycle consists of denaturation (separating DNA strands at about 94 C), annealing (primers binding to the target at 55-65 C), and extension (new strand synthesis at 72 C).

15. What is the approximate temperature used for the denaturation step in PCR?

    • A.37 degrees Celsius
    • B.55 degrees Celsius
    • C.72 degrees Celsius
    • D.94 degrees Celsius
    D. 94 degrees Celsius — Denaturation in PCR is carried out at approximately 94 degrees Celsius to separate the two strands of the double-stranded DNA template.

16. In blue-white screening, recombinant colonies appear as which colour?

    • A.Blue
    • B.White
    • C.Red
    • D.Yellow
    B. White — Recombinant colonies appear white because the foreign DNA insert disrupts the lacZ gene (insertional inactivation), so beta-galactosidase is not produced and the chromogenic substrate X-gal is not cleaved.

17. What is insertional inactivation?

    • A.Inserting a gene to activate a dormant gene
    • B.Disrupting a marker gene by inserting foreign DNA into it
    • C.Removing a gene to inactivate a cell
    • D.Silencing a gene using RNA interference
    B. Disrupting a marker gene by inserting foreign DNA into it — Insertional inactivation occurs when foreign DNA is inserted into a marker gene (such as lacZ), disrupting its function and allowing identification of recombinant clones.

18. What type of bioreactor is most commonly used in biotechnology?

    • A.Packed-bed bioreactor
    • B.Stirred-tank bioreactor
    • C.Airlift bioreactor
    • D.Fluidised-bed bioreactor
    B. Stirred-tank bioreactor — The stirred-tank bioreactor is the most commonly used type, featuring a mechanical stirrer (impeller) to mix contents and ensure even distribution of oxygen and nutrients.

19. What is the function of a sparger in a bioreactor?

    • A.To mix the culture medium
    • B.To introduce sterile air into the vessel
    • C.To control the temperature
    • D.To harvest the product
    B. To introduce sterile air into the vessel — A sparger introduces sterile air (or oxygen) into the bioreactor to supply the oxygen needed for aerobic growth of the cultured organisms.

20. What does downstream processing refer to?

    • A.The initial steps of DNA isolation
    • B.Separation and purification of the product after biosynthesis
    • C.The PCR amplification process
    • D.The transformation of host cells
    B. Separation and purification of the product after biosynthesis — Downstream processing is the series of steps used to separate, purify, and formulate the desired product after it has been produced in the bioreactor, including filtration, centrifugation, and chromatography.

References

• NCERT Solutions Class 12 Biology Chapter 11 - Biotechnology Principles and Processes (Byjus) — https://byjus.com/ncert-solutions-class-12-biology/chapter-11-biotechnology-principles-and-processes/
• Vedantu - Class 12 Biology Chapter 9 Biotechnology Principles and Processes — https://www.vedantu.com/ncert-solutions/ncert-solutions-class-12-biology-chapter-9-biotechnology-principles-and-processes
• Careers360 - NCERT Solutions Class 12 Biology Chapter 11 — https://school.careers360.com/ncert/ncert-solutions-class-12-biology-chapter-11-biotechnology-principles-and-processes