Biotechnology Principles and Processes ISC Class 12 Biology

What Biotechnology - Principles and Processes is about

Weightage: Biotechnology - Principles and Processes is part of the unit Biotechnology and its Applications, which carries 10 of the 70 marks in the ISC Biology Paper 1 (Theory), shared with 1 other chapter. Questions on it can appear in any section of the paper.Source: CISCE ISC Biology syllabus, examination year 2027, distribution of marks

Key concepts

Principles and tools of recombinant DNA technology

Genetic engineering creates recombinant DNA (rDNA) by joining DNA from different sources and introducing it into a host. A piece of foreign DNA cannot multiply on its own in the host; it must be linked to a DNA that has an origin of replication (ori), i.e. a vector (plasmid). The vector then replicates the linked DNA as it multiplies: cloning. Three basic tools: restriction enzymes (molecular scissors), DNA ligase (molecular glue) and vectors (carriers), plus a competent host. Plasmids are autonomously replicating circular extra-chromosomal DNA in bacteria. Cohen and Boyer (1972) made the first rDNA, transferring an antibiotic-resistance gene into E. coli plasmid with restriction enzymes and ligase; transformed E. coli multiplied the gene.

Worked example

Why can a piece of foreign DNA not simply be added to a bacterium to be copied? What solves this?

Try it first, then show the solutionSolution

1. Replication starts only at an origin of replication; most DNA fragments lack one that the host recognises.
2. The fragment is joined to a vector (plasmid) carrying an ori, so it replicates with the vector.

Answer: It lacks an ori; link it to a vector

Isolation of DNA and gel electrophoresis

Isolation of genomic DNA: DNA is enclosed by membranes and bound to other macromolecules. Cells are broken open (lysis) with enzymes: lysozyme (bacteria), cellulase (plant cells), chitinase (fungi). RNA is removed with ribonuclease, proteins (histones) with protease, other molecules by appropriate treatments. Chilled ethanol precipitates purified DNA, seen as a collection of fine threads (spooling). Gel electrophoresis separates DNA fragments: an agarose gel (a natural polymer from seaweeds) acts as a sieve; DNA, being negatively charged (phosphate groups), moves towards the anode (positive electrode) in an electric field; smaller fragments move farther. Fragments are visualised by staining with ethidium bromide and exposing to UV light: they appear as bright orange bands. The band of the gene of interest is cut out of the gel and DNA extracted (elution). The purified fragment is used to make rDNA.

Worked example

Two DNA fragments of 500 bp and 5000 bp are loaded in the same well of an agarose gel. Towards which electrode do they move, and which travels farther? Why?

Try it first, then show the solutionSolution

1. DNA is negatively charged (phosphate groups), so both move towards the anode (positive electrode).
2. The agarose matrix acts as a sieve: the smaller 500 bp fragment slips through the pores more easily and travels farther than the 5000 bp fragment.

Answer: Both to the anode; the 500 bp fragment travels farther

Restriction enzymes: discovery, nomenclature and action

Discovery: in 1963 two enzymes that restrict growth of bacteriophages in E. coli were isolated: one added methyl groups to DNA, the other cut DNA (restriction endonuclease). The first restriction endonuclease studied in detail was HindII, which always cuts DNA at a particular point by recognising a specific sequence of six base pairs (the recognition sequence). Over 900 are now known from more than 230 strains of bacteria. Nomenclature: first letter from the genus (capital), next two from the species, next letter from the strain, Roman numeral for the order of isolation. EcoRI: E = Escherichia, co = coli, R = strain RY13, I = first enzyme isolated from it. HindII: Haemophilus influenzae strain d, second. Action: exonucleases remove nucleotides from the ends; endonucleases cut within the DNA. Restriction endonucleases recognise palindromic sequences: the sequence reads the same on both strands when read in the same orientation (5'→3'), e.g. 5'-GAATTC-3' / 3'-CTTAAG-5'. They cut each strand a little away from the centre of the palindrome but between the same two bases on both strands, leaving single-stranded overhangs called sticky ends (EcoRI cuts G^AATTC, leaving 5'-AATT overhangs). Sticky ends form hydrogen bonds with complementary cut ends; DNA ligase then seals the phosphodiester backbone. Some enzymes (HindII) cut at the centre, giving blunt ends. The same enzyme must cut the vector and the source DNA so their ends are complementary.

Worked example

Name the restriction enzyme that is the third one isolated from strain d of Haemophilus influenzae, and show the cut of EcoRI on its site.

Try it first, then show the solutionSolution

1. Haemophilus → H, influenzae → in, strain d → d, third → III: HindIII.
2. EcoRI site 5'-G^AATTC-3' / 3'-CTTAA^G-5': fragments 5'-G and AATTC-3' on top; 3'-CTTAA and G-5' below, leaving AATT sticky ends.

Answer: HindIII; sticky ends with AATT overhangs

Cloning vectors and pBR322

Features of a good cloning vector: (1) origin of replication (ori), where replication starts and which controls the copy number of linked DNA; (2) selectable marker, which helps identify and eliminate non-transformants and selectively permits growth of transformants (genes for resistance to antibiotics such as ampicillin, chloramphenicol, tetracycline or kanamycin); (3) cloning (recognition) sites: preferably a single site for each commonly used restriction enzyme, so the vector is cut only once; ligation of foreign DNA at a site within an antibiotic-resistance gene allows insertional inactivation; (4) small size, easy isolation. pBR322 (an E. coli plasmid; p = plasmid, B = Bolivar, R = Rodriguez): has ori, rop (codes for proteins in replication), two antibiotic-resistance genes amp^R and tet^R, and unique sites for HindIII, EcoRI, BamHI, SalI, PvuII, PstI, ClaI. Other vectors: Agrobacterium tumefaciens (Ti plasmid, a natural genetic engineer of dicot plants causing tumours; disarmed Ti plasmid delivers genes into plants without causing tumours); retroviruses (disarmed, deliver genes into animal cells); BAC (bacterial artificial chromosome) and YAC (yeast artificial chromosome), which carry very large DNA inserts (used in the Human Genome Project).

Worked example

Why is it useful for a cloning vector such as pBR322 to carry two different antibiotic-resistance genes rather than one?

Try it first, then show the solutionSolution

1. One intact resistance gene (amp^R) lets transformed cells be selected: only cells with the plasmid grow on ampicillin.
2. The other gene (tet^R) contains cloning sites; an insert there inactivates it, so recombinants (tetracycline-sensitive) can be told apart from non-recombinants.

Answer: One marker selects transformants; the other identifies recombinants by insertional inactivation

Transfer of rDNA into a competent host

Since DNA is hydrophilic it cannot pass through cell membranes; the host must be made competent. Chemical/heat shock (direct method): bacterial cells are treated with a specific concentration of a divalent cation such as calcium (CaCl₂), which increases membrane permeability; rDNA is added; cells are incubated on ice, given a brief heat shock at 42 °C, and put back on ice; DNA enters. Microinjection: rDNA is injected directly into the nucleus of an animal cell with a fine needle. Biolistics (gene gun): plant cells are bombarded with high-velocity micro-particles of gold or tungsten coated with DNA. Disarmed pathogen vectors: Agrobacterium (plants) and retroviruses (animals) transfer DNA when allowed to infect cells. Other methods include electroporation.

Worked example

Which method is best for introducing a gene into (a) E. coli, (b) a mouse egg nucleus, (c) a wheat cell?

Try it first, then show the solutionSolution

1. (a) CaCl₂ treatment with heat shock (ice → 42 °C → ice).
2. (b) Microinjection. (c) Gene gun (biolistics) or Agrobacterium-mediated transfer.

Answer: Heat shock; microinjection; gene gun

Selection of recombinants: antibiotics and blue-white screening

After transformation, three kinds of cells exist: non-transformants (no plasmid), transformants with non-recombinant plasmid, and transformants with recombinant plasmid. Antibiotic resistance: with pBR322, a foreign gene ligated at the BamHI site in tet^R inactivates it. Plate on ampicillin: all transformants grow (amp^R intact). Replica plate on tetracycline: recombinants do not grow (tet^R inactivated), non-recombinants do. This is laborious (two plates). Insertional inactivation with a chromogenic substrate (blue-white selection): the vector carries the lacZα gene coding for β-galactosidase. The foreign DNA is inserted within this gene. On a medium with a chromogenic substrate (X-gal), colonies with an intact gene make β-galactosidase and turn blue (non-recombinants); colonies whose gene is interrupted by the insert cannot make the enzyme and stay white (recombinants). Only one plate is needed.

Worked example

E. coli cells are transformed with a plasmid carrying amp^R and lacZα, with the cloning site inside lacZα, and plated on ampicillin with X-gal. Predict the result for cells that took up (a) the recombinant plasmid, (b) a plasmid that re-closed without the insert, (c) no plasmid.

Try it first, then show the solutionSolution

1. (a) The insert interrupts lacZα, so no β-galactosidase forms and X-gal is not split: white colonies.
2. (b) lacZα is intact, β-galactosidase splits X-gal: blue colonies.
3. (c) No amp^R gene, so the cells are killed by ampicillin: no colonies.

Answer: White; blue; no growth

Gene amplification: cloning and PCR

In vivo amplification (cloning): the recombinant host cells multiply in culture, and with them the vector and the gene of interest. In vitro amplification by PCR (polymerase chain reaction), developed by Kary Mullis: multiple copies of a gene are made using two sets of primers (short chemically synthesised oligonucleotides complementary to the ends of the target region), deoxynucleotides and a thermostable DNA polymerase, Taq polymerase, isolated from the bacterium Thermus aquaticus, which remains active at the high temperature used for denaturation. Steps (one cycle): (1) denaturation at about 94 °C: double-stranded DNA separates; (2) annealing at about 50-60 °C: primers bind to complementary sequences; (3) extension at about 72 °C: Taq polymerase extends the primers. Each cycle doubles the DNA: after n cycles, up to 2ⁿ copies; about 30 cycles give roughly a billion copies. The amplified fragment can be ligated with a vector for cloning. Applications: detection of pathogens (HIV, cancer mutations) at very low levels, forensic DNA analysis, genetic diagnosis.

Worked example

Starting from one DNA molecule, how many copies does PCR give after 30 cycles? Why is Taq polymerase used?

Try it first, then show the solutionSolution

1. Copies = 2³⁰ = 1 073 741 824 ≈ 1.07 × 10⁹.
2. Taq polymerase from Thermus aquaticus is thermostable: it survives the 94 °C denaturation step, so fresh enzyme is not needed each cycle.

Answer: About 10⁹ copies; thermostable enzyme

Bioreactors and downstream processing

Bioreactors are large vessels (100-1000 litres) in which raw materials are converted into specific products by microbes, plant, animal or human cells, under optimal conditions of temperature, pH, substrate, salts, vitamins and oxygen. A sterile environment is essential (contaminating microbes would compete or spoil the product). Stirred-tank bioreactor: usually cylindrical or with a curved base to help mixing; a stirrer mixes contents evenly and distributes oxygen; air is introduced through a sparger; has an agitator system, an oxygen delivery system, a foam control system, a temperature control system, pH control system and sampling ports to withdraw small volumes periodically. Sparged-tank bioreactor: sterile air is bubbled (sparged) through the medium, which both mixes the contents and supplies oxygen, increasing the area for oxygen transfer (bubble type). Continuous culture: used medium is drained out from one side while fresh medium is added from the other, keeping cells in the exponential (log) phase for maximum biomass and product. Downstream processing: after biosynthesis the product is separated and purified, then formulated with suitable preservatives; for drugs, clinical trials and strict quality control testing are required before marketing; the process differs for each product.

Worked example

Why is a continuous culture system preferred in a bioreactor when large amounts of biomass or product are needed?

Try it first, then show the solutionSolution

1. Used medium is drained out from one side while fresh medium is added from the other.
2. This keeps the cells in the exponential (log) phase, where growth and product formation are fastest, and prevents accumulation of toxic wastes.

Answer: It keeps cells in the log phase for maximum yield

Biotechnology - Principles and Processes in real life

Each concept, met in an everyday situation. Read the situation, answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

Topics in this chapter

• Restriction Enzymes
• Cloning Vectors and pBR322
• Processes of Recombinant DNA Technology

Biotechnology - Principles and Processes: key facts

PCR amplification

$\text{copies after }n\text{ cycles}=2^n$

30 cycles ≈ 1.07 × 10⁹ copies.

Bacterial growth

$N=N_0\times 2^{t/g}$

g = doubling time; t/g = number of generations.

Expected frequency of a restriction site

$\text{one site every }{4}^n\text{ bp}$

4-bp site: every 256 bp; 6-bp site: every 4096 bp (random sequence).

PCR temperatures

$94{}^{\circ }C\text{(denature)}\to 50\text{-}60{}^{\circ }C\text{(anneal)}\to 72{}^{\circ }C\text{(extend)}$

Taq polymerase from Thermus aquaticus.

EcoRI cut

$5^{\prime }\text{-}G\downarrow AATTC\text{-}{3}^{\prime }$

Leaves 5' AATT sticky ends.

Enzyme naming

$\text{Genus (1)}+\text{species (2)}+\text{strain}+\text{order (Roman)}$

EcoRI, HindII, BamHI.

Biotechnology - Principles and Processes: diagrams to practise

Practise each one on paper: draw it from the checklist, then tick off every label.

How the board asks Biotechnology - Principles and Processes

The question patterns to expect, and the method that works for each.

Tricks to remember Biotechnology - Principles and Processes

Short memory aids. Say each one aloud once, then use it on a question the same day.

• Scissors, glue, carrier

  Restriction enzyme cuts, ligase joins, vector carries.

  Use it when: Tools of rDNA.

• Eco-R-I

  Escherichia coli, strain RY13, first enzyme.

  Use it when: Nomenclature.

• Blue = Bad (no insert), White = Win

  White colonies carry the recombinant.

  Use it when: Blue-white screening.

• PCR: 94-55-72

  Denature hot, anneal cool, extend warm.

  Use it when: PCR steps.

• Ori, Marker, Site

  OMS: the three features of a good vector.

  Use it when: Vector questions.

Biotechnology - Principles and Processes: board-level solved questions

Ordered from board level to HOTS. Cover the solution, write your own, then compare step by step.

Case-study practice (Section D style)

Read the situation, then answer every part. In the board paper this is a 5-mark question split into 1 + 1 + 1 + 2 marks.

Where the marks are

How a typical answer is split into step marks. Show every step: a right final answer alone rarely earns full marks.

Where students lose marks in Biotechnology - Principles and Processes

The slips examiners see most often, and what to write instead.

• ✗Mistake: Exponential growth treated as linear

  CISCE examiners' comments, 2025: for a bacterium doubling every 20 minutes for 3 hours, candidates found 9 doublings but answered 9 molecules instead of applying exponential growth (2⁹).

  Wrong working

  9 generations → 9 molecules.

  Right working

  9 generations → 2⁹ = 512 cells and molecules.

  ✓Do this: Number of cells = 2^(generations).

  Usually costs: 1 mark.

• ✗Mistake: Breaking nomenclature rules and misspelling names

  CISCE examiners' comments, 2025: for the fifth enzyme from E. coli strain RY13, candidates wrote EcoRy13V, EcoRyV or EcoR5; for the source of Taq polymerase they wrote methanogens, Taqupolitica or 'Thermophilic aquaticus'; in 2024 they wrote 'UV rays' for the gel stain or misspelt ethidium bromide.

  Wrong working

  EcoR5; Thermophilic aquaticus; ethylene bromide.

  Right working

  EcoRV; Thermus aquaticus; ethidium bromide.

  ✓Do this: Strain = one letter; order = Roman numeral; learn exact spellings.

  Usually costs: 1 mark each.

• ✗Mistake: Not explaining blue-white colours

  CISCE examiners' comments, 2025: candidates could not explain the reason for the colony colours, interchanged the colours of transformed and non-transformed colonies, or simply repeated 'blue colony' and 'white colony' without mentioning insertional inactivation.

  Wrong working

  Blue colonies are recombinant.

  Right working

  Insert inactivates lacZ; no β-galactosidase; colony stays white = recombinant.

  ✓Do this: Always name the gene, the enzyme and the substrate.

  Usually costs: 1-2 marks.

• ✗Mistake: Incomplete drawings of restriction fragments and vector choice

  CISCE examiners' comments, 2024 and 2025: candidates did not mention restriction sites or palindromes, drew fragments for only one enzyme, wrote 'blunt end' and 'sticky end' without drawing, or used boxes without base sequences; in choosing a vector, their chosen vector did not match their reasons and they did not understand the roles of ori, selectable marker and restriction site; and in a bioreactor assertion-reason item they confused options (b) and (d).

  Wrong working

  Two boxes labelled 'sticky end'.

  Right working

  Both strands with bases shown after cutting, for each enzyme.

  ✓Do this: Write sequences letter by letter and show where each strand is cut.

  Usually costs: 1-2 marks.

Practice questions on Biotechnology - Principles and Processes

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

1. Q1 · 1 mark · MCQBoard level

   In gel electrophoresis, DNA fragments move towards the:
   (a) cathode
   (b) anode
   (c) centre
   (d) both electrodes

   Hint

   DNA is negatively charged.

   Answer

   (b) anode

2. Q2 · 1 mark · MCQBoard level

   Which enzyme is used to break the cell wall of fungi during DNA isolation?
   (a) lysozyme
   (b) cellulase
   (c) chitinase
   (d) protease

   Hint

   Fungal walls contain chitin.

   Answer

   (c)

3. Q3 · 1 mark · Very short answerBoard level

   Name the bacterium called a natural genetic engineer of plants.

   Hint

   Crown gall.

   Answer

   Agrobacterium tumefaciens

4. Q4 · 1 mark · Very short answerBoard level

   What is the role of the rop gene in pBR322?

   Hint

   Replication.

   Answer

   It codes for proteins involved in replication of the plasmid.

5. Q5 · 1 mark · Very short answerHarder board level

   Why is chilled ethanol added during DNA isolation?

   Hint

   Precipitation.

   Answer

   DNA is insoluble in cold ethanol, so purified DNA precipitates out as fine threads that can be spooled.

6. Q6 · 2 marks · Short answerHarder board level

   A bacterium carrying a transgene doubles every 25 minutes. Starting from 4 cells, how many cells are there after 2 hours 30 minutes?

   Hint

   Generations = 150/25.

   Answer

   Generations = 6; cells = 4 × 2⁶ = 256.

7. Q7 · 2 marks · Short answerHarder board level

   Distinguish between stirred-tank and sparged-tank bioreactors.

   Hint

   Mixing method.

   Answer

   Stirred-tank: mechanical stirrer (impellers) mixes contents and disperses air supplied by a sparger. Sparged-tank: no stirrer; air bubbled through the medium both mixes it and supplies oxygen, increasing surface area for O₂ transfer.

8. Q8 · 2 marks · Short answerBoard level

   What is downstream processing? List its steps.

   Hint

   After biosynthesis.

   Answer

   Processing of the product after biosynthesis before marketing: separation, purification, formulation with preservatives, clinical trials (for drugs) and quality control testing.

9. Q9 · 2 marks · Short answerHarder board level

   Explain why a vector should have only one site for a particular restriction enzyme.

   Hint

   Multiple fragments.

   Answer

   Multiple sites would cut the vector into several fragments, complicating ligation and possibly removing essential parts (ori or markers); one site opens the circle once to accept the insert.

10. Q10 · 2 marks · Short answerHarder board level

    Why are BAC and YAC used in genome projects rather than pBR322?

    Hint

    Insert size.

    Answer

    BAC and YAC can carry very large DNA inserts (hundreds of kilobases to megabases), so fewer clones cover a whole genome; plasmids like pBR322 carry only small inserts.

11. Q11 · 5 marks · Long answerHarder board level

    (a) Describe the process of agarose gel electrophoresis. [3]
    (b) How is the separated DNA recovered? [1]
    (c) Why are smaller fragments found farther from the wells? [1]

    Hint

    Sieving.

    Answer

    (a) DNA samples are loaded into wells of an agarose gel in buffer; an electric field is applied; negatively charged DNA moves to the anode; fragments separate by size; gel is stained with ethidium bromide and viewed under UV as orange bands. (b) The band is cut out and the DNA extracted from the gel piece (elution). (c) The agarose matrix sieves molecules; smaller fragments pass through the pores more easily and travel farther.

12. Q12 · 2 marks · Short answerHOTS / competency

    A researcher gets no white colonies after blue-white screening although transformation worked. Suggest two reasons.

    Hint

    Insertion failed.

    Answer

    The insert did not ligate into the vector (vector re-closed on itself), or the insert was not placed within lacZα (e.g. vector and insert cut with incompatible enzymes), so lacZ stayed intact and all colonies were blue.

13. Q13 · 2 marks · Short answerHOTS / competency

    Why must PCR use primers for both strands, and what would happen if Taq polymerase were replaced by E. coli DNA polymerase?

    Hint

    Heat.

    Answer

    Each strand is a template, and DNA polymerase needs a primer on each to start synthesis, so the region between the two primers doubles every cycle. E. coli polymerase would be denatured at 94 °C, so fresh enzyme would be needed after every cycle and automation would fail.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1. 1.Who made the first recombinant DNA?Show answer

   Stanley Cohen and Herbert Boyer (1972).

2. 2.Which end of DNA does an exonuclease act on?Show answer

   The ends (removes terminal nucleotides).

3. 3.What is a selectable marker?Show answer

   A gene (often antibiotic resistance) that allows transformants to be identified and selected.

4. 4.What does EcoRI's 'R' stand for?Show answer

   Strain RY13.

5. 5.Name two antibiotic-resistance genes in pBR322.Show answer

   amp^R and tet^R.

6. 6.What is a competent cell?Show answer

   A host cell made able to take up DNA (e.g. by CaCl₂ treatment).

7. 7.Source of Taq polymerase?Show answer

   Thermus aquaticus.

8. 8.Expand YAC.Show answer

   Yeast artificial chromosome.

Quick revision checklist

The night before the exam: can you do each of these without looking?

• ☐Can you name the enzymes used to lyse bacterial, plant and fungal cells?
• ☐Can you explain gel electrophoresis and ethidium bromide staining?
• ☐Can you derive enzyme names and draw fragments after cutting?
• ☐Can you draw pBR322 and state three features of a good vector?
• ☐Can you describe heat shock, microinjection and gene gun?
• ☐Can you explain insertional inactivation and blue-white screening?
• ☐Can you describe PCR steps and calculate 2ⁿ copies?
• ☐Can you list components of a stirred-tank bioreactor and downstream steps?

Biotechnology - Principles and Processes: frequently asked questions