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Biotechnology: Principles and Processes – Class 12 Biology Chapter 9 Notes & NCERT PDF

Class 12BiologyChapter 9NCERT book: Biology - Class 12

Notes and a simple summary of Chapter 9 of the NCERT Class 12 Biology book, with the official chapter PDF, flashcards, an MCQ quiz and an AI tutor for your doubts.

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Chapter 9: Biotechnology: Principles and Processes

Introduction

Biotechnology deals with techniques of using live organisms or enzymes from organisms to produce products and processes useful to humans. Curd, bread and wine making are old forms of biotechnology, but today the term mostly refers to processes that use genetically modified organisms on a large scale, along with in vitro fertilisation, gene synthesis, DNA vaccines and gene correction. The European Federation of Biotechnology (EFB) defines it as 'the integration of natural science and organisms, cells, parts thereof, and molecular analogues for products and services'. The unit opens with Herbert Boyer, whose work on restriction enzymes with Stanley Cohen's work on plasmids founded the discipline.

Key Concepts

9.1 Principles of Biotechnology

Two core techniques enabled modern biotechnology:

  • Genetic engineering: altering the chemistry of genetic material (DNA and RNA), introducing it into host organisms and thus changing the host's phenotype.
  • Bioprocess engineering: maintaining a sterile (contamination-free) environment in chemical engineering processes so that only the desired microbe or eukaryotic cell grows in large quantities to make antibiotics, vaccines, enzymes and so on.
  • Traditional hybridisation often carries undesirable genes along with desired ones. Genetic engineering lets us introduce only the desired gene(s).
  • An alien piece of DNA usually cannot multiply in a new host unless it is linked to an origin of replication, a specific sequence where replication starts. Making multiple identical copies of a DNA template is cloning.
  • First recombinant DNA (1972): Stanley Cohen and Herbert Boyer cut an antibiotic resistance gene out of a plasmid of Salmonella typhimurium using restriction enzymes ('molecular scissors') and linked it to a plasmid vector using DNA ligase. Transferred into Escherichia coli, it replicated using the host's DNA polymerase: cloning of the antibiotic resistance gene in E. coli.
  • Three basic steps in genetically modifying an organism: (i) identify DNA with desirable genes; (ii) introduce it into the host; (iii) maintain it in the host and transfer it to the progeny.

    • 9.2 Tools of Recombinant DNA Technology

    Key tools: restriction enzymes, polymerase enzymes, ligases, vectors and the host organism.

    9.2.1 Restriction enzymes

  • In 1963 two enzymes restricting bacteriophage growth in E. coli were isolated: one added methyl groups to DNA, the other cut DNA (restriction endonuclease).
  • The first sequence-specific restriction endonuclease, Hind II, was isolated five years later; it cuts at a specific six base-pair recognition sequence. More than 900 restriction enzymes from over 230 bacterial strains are now known.
  • Naming: first letter from the genus, next two from the species, then the strain letter and a Roman numeral for order of isolation. EcoRI = Escherichia coli RY 13; 'R' is from the strain.
  • Nucleases are exonucleases (remove nucleotides from ends) or endonucleases (cut at specific positions within DNA).
  • Each restriction endonuclease recognises a palindromic sequence: it reads the same on both strands when read in the same orientation, e.g., 5'-GAATTC-3' paired with 3'-CTTAAG-5'.
  • They cut a little away from the centre of the palindrome, between the same two bases on opposite strands, leaving single-stranded overhangs called sticky ends. These form hydrogen bonds with complementary ends and help DNA ligase join them. Vector and source DNA must be cut with the same enzyme to get matching sticky ends.

    • Gel electrophoresis (separation and isolation of fragments):

  • DNA fragments are negatively charged, so they move towards the anode in an electric field.
  • The matrix is agarose, a natural polymer from sea weeds; it separates fragments by size through a sieving effect; smaller fragments move farther.
  • DNA is stained with ethidium bromide and seen as bright orange bands under UV light.
  • Bands are cut out and DNA extracted from the gel piece: elution.

    • 9.2.2 Cloning vectors

    Plasmids and bacteriophages replicate independently of chromosomal DNA; some plasmids have 1–2 copies per cell, others 15–100 or more. Features needed:

  • Origin of replication (ori): starts replication and controls the copy number of linked DNA.
  • Selectable marker: identifies and eliminates non-transformants; genes for resistance to ampicillin, chloramphenicol, tetracycline or kanamycin are used for E. coli.
  • Cloning sites: preferably single recognition sites for commonly used enzymes; many sites create several fragments and complicate cloning.
  • Vectors for plants and animals: the Ti plasmid of *Agrobacterium tumifaciens* (which normally delivers T-DNA to make plant tumours) has been disarmed into a cloning vector; disarmed retroviruses deliver genes into animal cells.

    • Selection in pBR322 (insertional inactivation): pBR322 has ori, rop, amp^R and tet^R genes and sites such as Hind III, EcoR I, BamH I, Sal I, Pvu II, Pst I and Cla I. Foreign DNA ligated at the BamH I site in the tetracycline resistance gene inactivates it.

  • Recombinants grow on ampicillin but not on tetracycline.
  • Non-recombinants grow on both antibiotics.

    • Because replica plating on two antibiotics is cumbersome, a chromogenic substrate method is preferred: insert DNA into the β-galactosidase coding sequence. Colonies without insert turn blue; recombinant colonies with the insert produce no colour.

    9.2.3 Competent host (transformation)

    DNA is hydrophilic and cannot pass through cell membranes. Bacteria are made competent by treating with a divalent cation such as calcium. Steps: incubate cells with recombinant DNA on ice → heat shock at 42°C briefly → back on ice. Other methods: micro-injection into the nucleus of animal cells; biolistics (gene gun) with gold or tungsten particles coated with DNA for plants; and disarmed pathogen vectors.

    9.3 Processes of Recombinant DNA Technology

  • Isolation of DNA (9.3.1): break cells using lysozyme (bacteria), cellulase (plant cells) or chitinase (fungus). Remove RNA with ribonuclease and proteins with protease. Purified DNA precipitates on adding chilled ethanol, seen as fine threads that can be spooled.
  • Cutting DNA at specific locations (9.3.2): incubate DNA with restriction enzyme under optimal conditions; check progress by agarose gel electrophoresis. Cut vector the same way, mix gene of interest with cut vector and add ligase to make recombinant DNA.
  • Amplification by PCR (9.3.3): Polymerase Chain Reaction uses two sets of primers (short chemically synthesised oligonucleotides) and DNA polymerase. Each cycle has denaturation, primer annealing and extension. Repeated cycles amplify the segment about a billion times. A thermostable polymerase from *Thermus aquaticus* (Taq polymerase) remains active during high-temperature denaturation.
  • Insertion into host (9.3.4): competent cells take up DNA; if it carries ampicillin resistance, only transformants grow on ampicillin plates; the ampicillin resistance gene is the selectable marker.
  • Obtaining the foreign gene product (9.3.5): a protein-encoding gene expressed in a heterologous host gives a recombinant protein. In a continuous culture system used medium drains out while fresh medium is added, keeping cells in the log/exponential phase for larger biomass. Bioreactors process 100–1000 litres, providing optimum temperature, pH, substrate, salts, vitamins and oxygen. The common stirred-tank bioreactor is cylindrical or curved-based, with an agitator, oxygen delivery system, foam control, temperature and pH control, and sampling ports; the sparged type bubbles sterile air through.
  • Downstream processing (9.3.6): separation and purification of the product, formulation with preservatives, clinical trials for drugs and strict quality control.

    • Diagrams to Know

  • EcoRI action: GAATTC palindrome cut between G and A on both strands, giving AATT sticky ends joined by ligase.
  • Agarose gel: wells at the cathode end, smaller bands farther towards the anode.
  • pBR322 map: ori, rop, amp^R, tet^R with restriction sites.
  • PCR cycle: denaturation, annealing, extension, repeated.
  • Stirred-tank bioreactor: motor, impeller, sparger, foam breaker, pH and temperature probes.

    • Key-Facts Sheet

  • First recombinant DNA: Cohen and Boyer, 1972.
  • Hind II: first sequence-specific restriction enzyme; recognises 6 bp.
  • Heat shock: 42°C. Bioreactor volume: 100–1000 litres.

    • Board Exam Focus

  • Describe origin of replication, bioreactors and downstream processing.
  • Explain PCR, restriction enzymes and chitinase.
  • Distinguish plasmid and chromosomal DNA, exonuclease and endonuclease.
  • Advantages of stirred-tank bioreactors over shake flasks; how reporter enzymes monitor transformation.

    • Key Terms

  • Recombinant DNA (पुनर्योगज डीएनए)
  • Restriction endonuclease (प्रतिबंधन एंडोन्यूक्लिएज)
  • Palindrome (पैलिंड्रोम / विलोमपद)
  • Sticky ends (चिपचिपे सिरे)
  • Vector (संवाहक)
  • Plasmid (प्लाज्मिड)
  • Selectable marker (वरण योग्य चिह्नक)
  • Insertional inactivation (निवेशी निष्क्रियता)
  • Transformation (रूपांतरण)
  • Gel electrophoresis (जेल वैद्युतकणसंचलन)
  • Elution (क्षालन)
  • Bioreactor (जैव रिएक्टर)
  • Downstream processing (अनुप्रवाह संसाधन)

    • Common Mistakes

  • Saying DNA moves to the cathode; negatively charged DNA moves to the anode.
  • Saying larger fragments travel farther; smaller ones travel farther.
  • Confusing colour results: blue colonies lack an insert; colourless colonies are recombinants.
  • Cutting vector and source DNA with different enzymes; matching sticky ends need the same enzyme.
  • Writing that Taq polymerase comes from E. coli; it comes from Thermus aquaticus.

    • 💡 Key Learning Points

    • ✓Modern biotechnology rests on genetic engineering and bioprocess engineering; Cohen and Boyer made the first recombinant DNA in 1972.
    • ✓Restriction endonucleases recognise palindromic sequences and create sticky ends that DNA ligase joins; fragments are separated by agarose gel electrophoresis and eluted.
    • ✓Cloning vectors need an origin of replication, selectable markers and single cloning sites; insertional inactivation (tet^R in pBR322 or β-galactosidase) identifies recombinants.
    • ✓DNA enters hosts through competence with calcium and heat shock, micro-injection, biolistics or disarmed pathogens such as the Ti plasmid.
    • ✓rDNA processes include DNA isolation, cutting, PCR amplification, insertion, expression in bioreactors and downstream processing.

    👨‍🏫 Teaching Tips

    • →Use scissors and glue on paper DNA strips with GAATTC written on them to demonstrate sticky ends and ligation.
    • →Draw the three steps of genetic modification as a simple three-box flow chart before introducing tools.
    • →Show a gel photograph and ask students which end the samples were loaded at and which band is smallest.
    • →Walk through pBR322 selection with two petri dish sketches (ampicillin and tetracycline) and let students predict colony growth.
    • →Model PCR by doubling paper copies for five cycles to show exponential amplification.
    • →Label a stirred-tank bioreactor diagram part by part and compare it with a shake flask.
    • →Assign each student an enzyme (lysozyme, ribonuclease, protease, ligase, Taq polymerase) to explain its role in 30 seconds.

    📋 Assessment Questions

    1. Can the student explain the naming of restriction enzymes and why they create sticky ends?
    2. Can the student describe agarose gel electrophoresis and elution?
    3. Can the student list features of a cloning vector and explain insertional inactivation?
    4. Can the student describe the steps of PCR and the role of Taq polymerase?
    5. Can the student describe a stirred-tank bioreactor and downstream processing?

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    Keep learning

    All chapters in Biology - Class 12

    1. 1. Sexual Reproduction in Flowering Plants
    2. 2. Human Reproduction
    3. 3. Reproductive Health
    4. 4. Principles of Inheritance and Variation
    5. 5. Molecular Basis of Inheritance
    6. 6. Evolution
    7. 7. Human Health and Disease
    8. 8. Microbes in Human Welfare
    9. 9. Biotechnology: Principles and Processes
    10. 10. Biotechnology and its Applications
    11. 11. Organisms and Populations
    12. 12. Ecosystem
    13. 13. Biodiversity and Conservation