Biotechnology: Principles and Processes - Class 12 Biology

Class 12 Biology | Unit XI — Biotechnology

Chapter 11: Biotechnology — Principles and Processes

Recombinant DNA • Restriction Enzymes • Vectors • PCR • Gel Electrophoresis • Bioreactors

1. Principles of Biotechnology

Biotechnology: The use of living organisms or their products to make or modify products or processes for specific use. European Federation of Biotechnology (EFB) definition: Integration of natural science and organisms, cells, parts thereof, and molecular analogues for products and services.

1.1 Two Core Techniques

Genetic engineering (rDNA technology): Alter DNA of an organism to obtain desired characteristics. Key: insert foreign DNA into host.
Maintaining sterile conditions (aseptic/bioprocess technology): Growing microbes, plant/animal cells in contamination-free environment to produce antibiotics, vaccines, enzymes, etc.

1.2 Recombinant DNA Technology — Tools Required

Restriction enzymes (molecular scissors)
Vectors (vehicles to carry foreign DNA into host)
Host organism (where recombinant DNA is expressed)
PCR (to amplify DNA)
Gel electrophoresis (to separate DNA fragments)

2. Tools of Recombinant DNA Technology

2.1 Restriction Enzymes

Restriction endonucleases: Enzymes that recognise specific palindromic sequences in DNA and cut the DNA at or near those sequences. Named after the source bacteria: First letter = genus, 2nd & 3rd = species, 4th = strain, Roman numeral = order of discovery.

First restriction enzyme identified: Hind II — always cuts double-stranded DNA at a specific point by recognising a specific sequence of 6 base pairs.
EcoRI: from Escherichia coli strain R. Cuts between G and A in sequence 5'-GAATTC-3'. Produces sticky ends (cohesive ends with single-stranded overhangs).
Sticky ends: Single-stranded overhangs that can base-pair with complementary sequences. Facilitate joining by DNA ligase.
Blunt ends: No overhangs. Example: Hae III.
Palindromic sequence: A sequence that reads identically on both strands in 5' to 3' direction.
5'-GAATTC-3' / 3'-CTTAAG-5' — standard palindrome.
DNA ligase seals the nicks after joining.

2.2 Vectors

Vectors: DNA molecules used to carry foreign DNA into host cells for cloning and expression. Must have: (a) origin of replication (ori), (b) selectable marker, (c) cloning sites (MCS — multiple cloning site).

Vector	Type	Insert Size / Feature
Plasmid	Circular extra-chromosomal DNA (bacteria)	Small inserts (<10 kb). pBR322 = first artificial recombinant plasmid. Contains Amp^R (ampicillin) and Tet^R (tetracycline) resistance genes.
Lambda phage (λ)	Bacteriophage	Moderate inserts (up to 25 kb). Non-essential DNA region replaced by foreign DNA.
Cosmids	Hybrid (plasmid + phage)	Large inserts (35–45 kb). Contain cos sites of lambda phage.
BAC	Bacterial Artificial Chromosome	Very large inserts (100–300 kb). Used in genome projects.
YAC	Yeast Artificial Chromosome	Largest inserts (>1 Mb). Used for large genomes.

2.3 Selectable Markers and Insertional Inactivation

pBR322: Contains Amp^R and Tet^R genes + BamHI, SalI, ClaI restriction sites within Tet^R.
Insertional inactivation: When foreign DNA is inserted into Tet^R via BamHI → Tet^R gene disrupted → bacteria grows on Amp plates (have vector) but NOT on Tet plates (no Tet^R) → recombinants identified.
Blue-white selection (β-gal assay): Insert into lacZ gene → no β-galactosidase → white colonies = recombinants; blue = non-recombinants (with X-gal substrate).

3. Polymerase Chain Reaction (PCR)

PCR: In vitro method to amplify specific segments of DNA millions of times using repeated cycles of: Denaturation → Annealing → Extension (Synthesis). Invented by Kary Mullis (Nobel Prize 1993).

Steps per cycle:
1. Denaturation (94°C): Double-stranded DNA heated → strands separate.
2. Annealing (50–65°C): Short primers (oligonucleotides, ~20 bp, flanking the target) anneal to complementary single strands.
3. Extension/Synthesis (72°C): Taq DNA polymerase (thermostable, from Thermus aquaticus) extends the primers using dNTPs → new DNA strands.
n cycles → 2ⁿ copies of target DNA.

Taq polymerase: thermostable, withstands 94°C denaturation. Optimum at 72°C.
Primers: Small DNA sequences that define the region to be amplified. Must be complementary to flanking regions.
30 cycles → approximately 10⁹ copies (2³⁰ ≈ 10⁹) from a single template.
Used in: DNA fingerprinting, forensics, diagnostics, cloning, sequencing.

⚠️ NEET Focus (2014, 2016, 2019, 2021): PCR = Kary Mullis. 3 steps: Denaturation (94°C) → Annealing → Extension (72°C). Taq polymerase = from Thermus aquaticus, thermostable. In PCR cycle n: 2ⁿ copies. EcoRI cuts 5'-GAATTC-3', produces sticky ends. pBR322 = first artificial recombinant plasmid (Bolivar and Rodriguez).

4. Gel Electrophoresis

Gel Electrophoresis: Technique to separate DNA (or RNA/protein) fragments based on size. DNA fragments migrate through an agarose gel matrix under electric field toward positive electrode (anode) — because DNA is negatively charged (phosphate groups).

Smaller fragments migrate farther (faster). Larger fragments are closer to wells.
DNA bands visualised by staining with ethidium bromide (EtBr) — intercalates into DNA; fluoresces under UV light.
Known size DNA Ladder (marker) run alongside for comparison.
Southern Blotting (DNA), Northern Blotting (RNA), Western Blotting (protein).

5. Steps in Recombinant DNA Technology

Isolation of the desired DNA (gene of interest or GOI) using restriction enzymes.
Fragmentation: Restriction digestion of DNA and vector with same enzyme → compatible sticky ends.
Ligation: Join GOI into vector using DNA ligase → recombinant DNA (rDNA).
Transformation: Introduce rDNA into host cell.
- Chemical method: E. coli treated with divalent cations (CaCl₂) → competent cells → heat shock (42°C) → DNA enters.
- Electroporation: Brief electrical pulses create pores in membrane → DNA enters.
- Micro-injection: DNA injected directly into nucleus (animal cells).
- Biolistics (Gene gun): DNA-coated gold/tungsten particles fired into plant cells.
- Disarmed pathogen vectors: Agrobacterium tumefaciens (Ti plasmid) for plants.
Selection of recombinants: Insertional inactivation, blue-white screening, antibiotic resistance.
Expression: Recombinant host expresses foreign gene → desired protein produced.

5.1 Bioreactors

Bioreactor: Vessel where biological processes are carried out to produce desired product on large scale using recombinant organisms. Provides optimal conditions (temperature, pH, O₂, nutrients, agitation).

Stirred-tank bioreactor: Most common. Has impeller for mixing, O₂ supply, pH/temp control, foam control (antifoam), outlet for product.
Sparged stirred-tank: Sterile air bubbled in through sparger.
Products obtained: Insulin, erythropoietin, interferons, vaccines, antibiotics, enzymes.

⚠️ NEET Focus (2015, 2018, 2020, 2022): Restriction enzyme = molecular scissors. EcoRI cuts GAATTC = sticky ends. pBR322 = Amp^R + Tet^R (first artificial plasmid). Biolistics = gene gun (gold particles). Agrobacterium Ti plasmid = natural vector for plants. Bioreactor = stirred tank = large-scale production. Gel electrophoresis: DNA → anode; smaller fragments travel farther; EtBr staining + UV.

🎓 Key NEET Questions

Q1. [NEET 2022] In gel electrophoresis, the DNA fragments are:

(a) Separated on the basis of charge only (b) Separated based on size; smaller fragments migrate farther (c) Stained with safranin (d) Separated toward negative electrode

Answer: (b) DNA is negatively charged (phosphate groups) → migrates toward anode (positive electrode). Smaller fragments migrate faster and farther; larger fragments are slower. Stained with ethidium bromide, visualised under UV light.

Q2. [NEET 2021] Which enzyme is used to amplify DNA in PCR?

(a) Taq polymerase (b) Restriction endonuclease (c) DNA ligase (d) RNA polymerase

Answer: (a) Taq polymerase — a thermostable DNA polymerase isolated from the thermophilic bacterium Thermus aquaticus. Used in PCR because it withstands repeated heating to 94°C (denaturation step) without getting denatured. Optimum activity at 72°C.

Q3. [NEET 2020] The recognition sequence of EcoRI is:

Answer EcoRI recognises the palindromic sequence 5'-GAATTC-3' and cuts between G and A, producing sticky ends:
5'-G     AATTC-3'
3'-CTTAA  G-5'
The overhang (5'-AATT-3') = sticky/cohesive end. Complementary sticky ends from different DNA molecules can be joined by DNA ligase.

Q4. [NEET 2019] Which of the following is the selectable marker in pBR322 plasmid?

(a) Tetracycline resistance and chloramphenicol resistance (b) Ampicillin resistance and kanamycin resistance (c) Ampicillin resistance and tetracycline resistance (d) Kanamycin resistance only

Answer: (c) pBR322 contains two antibiotic resistance genes as selectable markers: Amp^R (ampicillin resistance) and Tet^R (tetracycline resistance). These allow selection of bacteria that have taken up the plasmid and identification of recombinants (via insertional inactivation of Tet^R).

Q5. [NEET 2018] What is the role of DNA ligase in recombinant DNA technology?

Answer DNA ligase is the “molecular glue” or sealing enzyme. After restriction enzymes cut the vector and insert DNA leaving complementary sticky ends that hydrogen-bond together, DNA ligase seals the phosphodiester bonds between the nicks in the sugar-phosphate backbone → forms a covalently closed, stable recombinant DNA molecule. Without ligase, the inserted fragment would remain loosely associated.

💡 Rapid Revision — Key Points

Two core biotech techniques: Genetic Engineering + Bioprocess Technology.
Restriction enzymes: molecular scissors; cut at palindromic sequences; produce sticky or blunt ends.
EcoRI: 5'-GAATTC-3'; cuts between G and A; sticky ends.
pBR322: Amp^R + Tet^R; insertional inactivation in Tet^R.
PCR: Kary Mullis; Denature → Anneal → Extend; Taq polymerase; 2ⁿ copies per n cycles.
Gel electrophoresis: DNA → anode; smaller = farther; EtBr staining.
Gene gun / Biolistics: gold particles + DNA for plant transformation.
Agrobacterium Ti plasmid = natural delivery system for plant gene transfer.
Bioreactor (stirred-tank): large-scale production; maintains optimal conditions.

NCERT Solutions - Biotechnology Principles and Processes - Class 12

CLASS 12 BIOLOGY | NCERT SOLUTIONS

Chapter 11 — Biotechnology: Principles and Processes

All NCERT Exercise Questions with Detailed Solutions

📋 Note: All questions from NCERT Class 12 Biology Chapter 11 Exercise.

NCERT Exercise Questions & Solutions

2 MarksQ1. Can you list 10 recombinant proteins which are used in medical practice? Find out where they are used as therapeutics.

✓ Answer

#	Recombinant Protein	Medical Use
1	Insulin (Humulin)	Treatment of diabetes mellitus (Type 1, Type 2)
2	Human Growth Hormone	Growth hormone deficiency in children (dwarfism)
3	Erythropoietin	Anaemia (stimulates RBC production)
4	Interferon-α	Viral infections, some cancers (hairy cell leukaemia)
5	Tissue plasminogen activator (tPA)	Dissolves blood clots in heart attack, stroke
6	Factor VIII	Haemophilia A (clotting factor replacement)
7	Factor IX	Haemophilia B (Christmas disease)
8	Hepatitis B vaccine	Prevention of Hepatitis B (surface antigen)
9	Interleukin-2	Immunotherapy for cancer
10	DNase I (Pulmozyme)	Cystic fibrosis (breaks mucus DNA)

3 MarksQ2. What are restriction enzymes? How do they function? Give two examples.

✓ Answer
Restriction enzymes (restriction endonucleases): Enzymes that recognise specific, short palindromic sequences (recognition sites) in double-stranded DNA and cleave both strands at or near those sites. Called “molecular scissors”.

Function:

Recognition: Enzyme scans DNA and binds to specific palindromic sequence (6-8 bp).
Cleavage: Enzyme cuts both strands of DNA — either at same point (blunt ends) or staggered cuts (sticky/cohesive ends with single-stranded overhangs).

Two examples:

EcoRI: From E. coli strain R. Recognises 5'-GAATTC-3'. Cuts between G and A. Produces 5' sticky ends (5'-AATT overhangs).
BamHI: From Bacillus amyloliquefaciens H. Recognises 5'-GGATCC-3'. Produces 5' sticky ends (5'-GATC overhangs).

Note: The first restriction enzyme discovered was Hind II.

3 MarksQ3. What are the key tools of recombinant DNA technology?

✓ Answer
Key tools of recombinant DNA technology:

Restriction endonucleases: Cut DNA at specific palindromic sequences — “molecular scissors”.
DNA ligase: Joins (seals) DNA fragments — “molecular glue”. Seals phosphodiester bonds.
Vectors: Carry and replicate foreign DNA in host. Examples: plasmid (pBR322), bacteriophage (lamda), cosmid, BAC, YAC.
Host cell: Provides machinery for replication and expression. Examples: E. coli, yeast, Agrobacterium.
Polymerase Chain Reaction (PCR): Amplify specific DNA segments exponentially using Taq polymerase.
Gel electrophoresis: Separate and identify DNA fragments by size.
DNA probes / Southern blotting: Detect specific sequences.

5 MarksQ4. Explain the role of the following in biotechnology: (a) Restriction enzyme (b) DNA ligase (c) Selectable marker (d) Vector.

✓ Answer

Tool	Role in Biotechnology
(a) Restriction enzyme	Cuts both insert DNA and vector DNA at specific palindromic sequences, generating compatible ends (sticky or blunt). Ensures precise cutting so foreign gene can be inserted into vector at the correct location.
(b) DNA ligase	After insert is annealed to vector via complementary sticky ends, DNA ligase covalently seals the sugar-phosphate backbone (phosphodiester bonds) → stable recombinant DNA molecule. Without it, insert would be lost.
(c) Selectable marker	Gene in vector (e.g., antibiotic resistance: Amp^R, Tet^R) that allows selection of transformed cells. Only cells with vector survive antibiotic treatment. Insertional inactivation or blue-white screening identifies recombinants vs non-recombinants.
(d) Vector	DNA molecule that carries foreign DNA into host cells, provides origin of replication (ori) for autonomous replication and cloning sites (MCS). Ensures foreign DNA is maintained and replicated within host. Examples: pBR322 plasmid, lambda phage.

5 MarksQ5. Describe the process of PCR (Polymerase Chain Reaction) with diagram.

✓ Answer
PCR (Polymerase Chain Reaction): An in vitro technique for amplifying specific DNA sequences exponentially. Invented by Kary Mullis (1983, Nobel Prize 1993).

Requirements:

Template DNA (target DNA)
DNA primers (short oligonucleotides, ~20 bp, specific to flanking sequences)
Taq DNA polymerase (thermostable, from Thermus aquaticus)
dNTPs (dATP, dTTP, dGTP, dCTP)
Buffer with Mg²⁺

3 Steps per cycle:

Denaturation (94–96°C, ~30 sec): ds-DNA heated → hydrogen bonds break → two single strands separate.
Annealing (50–65°C, ~30 sec): Temperature lowered → primers anneal to complementary sequences on each single strand template.
Extension/Synthesis (72°C, ~1–2 min): Taq polymerase synthesises new DNA strand 5'→3' using template, starting from primer. dNTPs added.

One cycle = original 1 DNA → 2 DNA. After n cycles = 2ⁿ copies. Typically 30–35 cycles → ~10⁹ copies.

Significance: Forensics, prenatal diagnosis, pathogen detection, sequencing, cloning.

3 MarksQ6. How is pBR322 used as a cloning vector? Describe its essential characteristics.

✓ Answer
pBR322 (p = plasmid; BR = Bolivar and Rodriguez who constructed it; 322 = identification number) is the most commonly used cloning vector.

Essential characteristics:

Origin of replication (ori): Sequence that allows autonomous replication in E. coli. Ensures vector (and insert) are replicated.
Selectable markers: Two: Amp^R (ampicillin resistance) and Tet^R (tetracycline resistance).
Multiple cloning sites: BamHI, SalI, ClaI sites within Tet^R; EcoRI, ClaI sites elsewhere.
Small size (4.36 kb): Easy to handle and transform.

Insertional inactivation strategy:
Insert foreign DNA at BamHI site (within Tet^R) → Tet^R disrupted. Plate on Amp: all transformants grow. Replica plate on Tet: non-transformants and non-recombinants grow; recombinants do NOT grow on Tet (identified by absence of growth on Tet plates).

Facts Capsule - Biotechnology Principles and Processes - Class 12

CLASS 12 BIOLOGY | NEET RAPID CAPSULE

Facts & High-Yield Points

Chapter 11 — Biotechnology: Principles and Processes | 18 Key Facts for NEET

✂️ Restriction Enzymes

FACT #01 — Naming of Restriction Enzymes

Named after source organism: 1st letter = genus, 2nd & 3rd = species, 4th = strain, Roman numeral = order. EcoRI = Escherichia coli strain R, 1st enzyme. First RE discovered = Hind II.

FACT #02 — EcoRI Recognition

Palindromic sequence: 5'-GAATTC-3'. Cuts between G and A. Produces 5' sticky ends (5'-AATT overhangs). Complementary sticky ends joined by DNA ligase.

FACT #03 — Sticky vs Blunt Ends

Sticky (cohesive) ends: staggered cuts → single-stranded overhangs. Better for ligation. Example: EcoRI. Blunt ends: straight cuts, no overhangs. Example: Hae III. Sticky ends preferred in cloning.

📚 Vectors

FACT #04 — Ideal Vector Features

Must have: (1) ori (origin of replication), (2) Selectable marker (antibiotic resistance), (3) Cloning sites (MCS). Small size preferred for easy handling.

FACT #05 — pBR322

First artificial recombinant plasmid (Bolivar and Rodriguez). 4.36 kb. Has Amp^R + Tet^R. Restriction sites within Tet^R (BamHI, SalI, ClaI). Insertional inactivation at Tet^R identifies recombinants.

FACT #06 — Vector Capacities

Plasmid: <10 kb. Lambda phage: up to 25 kb. Cosmid: 35–45 kb. BAC: 100–300 kb. YAC: >1 Mb. Larger inserts need larger vectors (chromosome-level).

📈 PCR

FACT #07 — PCR Steps

Kary Mullis (1983, Nobel 1993). 3 steps: (1) Denaturation (94°C) — strands separate. (2) Annealing (50–65°C) — primers bind. (3) Extension (72°C) — Taq polymerase extends.

FACT #08 — Taq Polymerase

From Thermus aquaticus (hot springs bacterium). Thermostable — survives 94°C cycles. Optimum at 72°C. Copies → 2ⁿ after n cycles. 30 cycles → ~10⁹ copies.

🧬 Process & Tools

FACT #09 — Steps in rDNA Technology

(1) Isolate GOI (2) Restriction digestion (3) Ligation into vector (4) Transformation into host (5) Selection of recombinants (6) Expression of GOI.

FACT #10 — Transformation Methods

Chemical: CaCl₂ + heat shock (42°C) for E. coli. Electroporation: electric pulses. Gene gun/Biolistics: gold particles + DNA. Agrobacterium Ti plasmid: natural vector for plants. Micro-injection: animal cells.

FACT #11 — Gel Electrophoresis

DNA = negatively charged → migrates to anode (+). Smaller fragments travel farther. Medium = agarose gel. Stained with ethidium bromide (EtBr); visualised under UV. DNA ladder used as size marker.

FACT #12 — Bioreactor

Stirred-tank bioreactor: most common. Has impeller, sparger (O₂), pH/temp sensors, foam controller. Used for large-scale production of recombinant proteins. Includes upstream (culture) and downstream (purification) processes.

🧠 Mnemonics — Remember Fast

PCR Steps: “DAE” Denaturation (94°C) → Annealing (50–65°C) → Extension (72°C). Taq polymerase (thermostable). 2ⁿ copies after n cycles. Kary Mullis 1983.

EcoRI Palindrome: “GAATTC” 5'-G-A-A-T-T-C-3' / 3'-C-T-T-A-A-G-5'. Cut between G and A → 5'-AATT sticky ends. DNA ligase joins. First RE = Hind II.

pBR322: “Amp + Tet” Amp^R + Tet^R. BamHI/SalI/ClaI in Tet^R. Insert in Tet^R → grows on Amp but NOT Tet = recombinant. Blue-white: lacZ disruption → white=recombinant.

Transformation: “BEAM-G” Biolistics (gene gun). Electroporation. Agrobacterium Ti plasmid. Micro-injection. Chemical = CaCl₂ + heat shock (42°C) for E. coli.

🔢 Critical Numbers — Never Forget

1983 — Kary Mullis invented PCR 1993 — Nobel Prize for PCR 2ⁿ — copies after n PCR cycles 72°C — Taq polymerase optimum 94°C — denaturation temperature GAATTC — EcoRI recognition sequence 4.36 kb — pBR322 size Hind II — first restriction enzyme

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