Biotechnology: Principles and Processes

2.1 Core concepts

• Biotechnology = techniques using live organisms / enzymes / cells to produce useful products and processes; modern restricted sense uses genetically modified organisms at large scale. (NCERT §9 intro, p. 163)
• The European Federation of Biotechnology (EFB) definition: "The integration of natural science and organisms, cells, parts thereof, and molecular analogues for products and services." (NCERT §9 intro, p. 163)
• Two core techniques enabled modern biotechnology: (i) genetic engineering — altering chemistry of genetic material (DNA/RNA) and introducing it into host to change phenotype; (ii) bioprocess engineering — sterile chemical-engineering ambience for desired microbe/eukaryotic-cell growth at large scale (antibiotics, vaccines, enzymes). (NCERT §9.1, p. 163-164)
• An alien piece of DNA cannot multiply in a host unless linked to an origin of replication (ori) — the specific chromosomal sequence that initiates replication. Cloning = making multiple identical copies of any template DNA. (NCERT §9.1, p. 164)
• The first artificial recombinant DNA was constructed by Stanley Cohen and Herbert Boyer in 1972 by linking an antibiotic-resistance gene to a native plasmid of Salmonella typhimurium using restriction enzymes ("molecular scissors") and DNA ligase, then transferring it into E. coli. (NCERT §9.1, p. 164-165)
• Three basic steps of GM: (i) identification of DNA with desirable genes; (ii) introduction into the host; (iii) maintenance of introduced DNA in host and transfer to progeny. (NCERT §9.1, p. 165)
• Restriction endonucleases — first such enzyme Hind II (characterised 1968) recognises a specific 6-bp recognition sequence. Over 900 restriction enzymes from 230+ bacterial strains are now known. (NCERT §9.2.1, p. 165)
• Nomenclature: first letter = genus, next two letters = species, then strain letter, then Roman numeral for order of isolation, e.g. EcoRI = Escherichia coli RY 13, first enzyme. (NCERT §9.2.1, p. 165-166)
• Nucleases come in two kinds: exonucleases (remove nucleotides from ends) and endonucleases (cut at specific internal positions). (NCERT §9.2.1, p. 166)
• Restriction enzymes recognise palindromic sequences — read same on both strands in 5'→3'; cut a little away from centre of palindrome between the same two bases on opposite strands, leaving overhanging single-stranded sticky ends which hydrogen-bond with complementary cut counterparts and facilitate DNA ligase action. (NCERT §9.2.1, p. 166-167)
• Gel electrophoresis — DNA fragments (negatively charged) move toward the anode through an agarose matrix (natural polymer from sea weeds); smaller fragments migrate farther; bands visualised by staining with ethidium bromide under UV light (bright orange bands); recovery of bands by cutting and elution. (NCERT §9.2.1, p. 168)
• Cloning vector features: (i) ori controls copy number; (ii) selectable marker (antibiotic resistance — amp, tet, kan, chloramphenicol) lets you eliminate non-transformants; (iii) cloning sites — preferably single recognition sites for common restriction enzymes; (iv) modified pathogen-derived vectors for plant/animal cells. (NCERT §9.2.2, p. 169-170)
• pBR322 (E. coli cloning vector): carries ori, rop (replication-protein gene), ampR and tetR resistance genes, and unique restriction sites — Hind III, EcoR I, BamH I, Sal I, Pvu II, Pst I, Cla I. Foreign DNA ligated at BamH I (in tetR) inactivates tetR; recombinants grow on amp but not on tet (insertional inactivation of antibiotic resistance). (NCERT §9.2.2, p. 169)
• Alternative selectable marker — insertional inactivation of β-galactosidase: insertion-bearing colonies are colourless on chromogenic substrate; non-insert colonies are blue. (NCERT §9.2.2, p. 170)
• Vectors for eukaryotes: Ti plasmid of Agrobacterium tumefaciens (disarmed; for dicot plants) and disarmed retroviruses for animal cells. (NCERT §9.2.2, p. 170)
• Competent host: bacterial cells made competent by treatment with a divalent cation (Ca²⁺); rDNA enters via heat shock (ice → 42 °C → ice). Other delivery methods: micro-injection (animal nucleus), biolistics / gene gun (plant cells, gold/tungsten micro-particles), disarmed pathogen vectors. (NCERT §9.2.3, p. 170-171)
• Processes of rDNA technology (sequence): isolation of DNA → fragmentation with restriction enzymes → isolation of desired fragment → ligation into vector → transfer to host → culture → product extraction. (NCERT §9.3, p. 171)
• DNA isolation: cell-wall lysis with lysozyme (bacteria), cellulase (plants), chitinase (fungi); ribonuclease removes RNA; protease removes proteins; purified DNA precipitates as fine threads on adding chilled ethanol (collected by spooling). (NCERT §9.3.1, p. 171)
• PCR (Polymerase Chain Reaction) — three steps per cycle: (i) Denaturation (heat), (ii) Primer annealing (two short chemically-synthesised oligonucleotides complementary to template), (iii) Extension by thermostable Taq polymerase from Thermus aquaticus; ~30 cycles amplify ~1 billion times. (NCERT §9.3.3, p. 172-173)
• A protein-encoding gene expressed in a heterologous host gives a recombinant protein; large-scale production needs bioreactors processing 100-1000 L; bioreactors maintain optimal temperature, pH, substrate, salts, vitamins and oxygen. (NCERT §9.3.5, p. 173-174)
• Stirred-tank bioreactor — cylindrical or curved-base vessel with agitator (stirrer), oxygen-delivery system, foam-control system, temperature- and pH-control systems and sampling ports. Sparged stirred-tank bioreactor passes sterile air bubbles for greater oxygen transfer area. (NCERT §9.3.5, p. 174)
• Downstream processing = post-biosynthetic separation, purification, formulation with preservatives, clinical trials and quality-control testing; varies from product to product. (NCERT §9.3.6, p. 174-175)

2.2 Definitions to memorise

2.3 Diagrams / processes to remember

• Figure 9.1, p. 166 — Action of EcoRI: cuts between G and A of the palindrome GAATTC / CTTAAG on vector and foreign DNA, generates sticky ends, which ligate to form recombinant DNA.
• Figure 9.2, p. 167 — Flowchart of rDNA technology: same restriction enzyme cuts both foreign DNA and vector plasmid → ligase joins → recombinant DNA → transformation into E. coli (cloning host) → cells divide.
• Figure 9.3, p. 168 — Agarose gel electrophoresis: wells at the cathode end (top); bands of largest fragments stay near wells, smallest run farthest toward anode; bright orange bands under UV after ethidium-bromide staining.
• Figure 9.4, p. 169 — pBR322 map: ori, rop, ampR, tetR, and unique restriction sites Hind III, EcoR I, BamH I, Sal I, Pvu II, Pst I, Cla I.
• Figure 9.5, p. 171 — DNA spooling: fine thread-like precipitate of purified DNA after addition of chilled ethanol, lifted out with a rod.
• Figure 9.6, p. 172 — PCR cycle: (i) Denaturation (heat) → ssDNA; (ii) Annealing of two primers; (iii) Extension by Taq DNA polymerase; repeated for ~30 cycles to amplify ~1 billion times.
• Figure 9.7, p. 174 — (a) Simple stirred-tank bioreactor: motor, foam-breaker, acid/base for pH, steam for sterilisation, flat-bladed impeller, culture broth, sterile-air inlet; (b) Sparged stirred-tank: sterile air bubbles sparged for increased oxygen-transfer area.

2.4 Common confusions / NTA trap points

• EcoRI nomenclature: the "R" stands for the strain (RY 13), NOT for "restriction." NTA loves to swap "R = restriction" as a distractor. (p. 165-166)
• **Sticky ends are produced because the enzyme cuts away from the centre of the palindrome** but between the same two bases on opposite strands — students sometimes write "cut at the centre" which would give blunt ends.
• pBR322 selection logic: insertion at BamH I in tetR → recombinants grow on amp but NOT on tet; non-recombinants grow on both. Don't flip the resistance pattern.
• Taq polymerase is from Thermus aquaticus, not from E. coli. Its key property is thermostability so it survives 94 °C denaturation.
• Lysozyme = bacteria, cellulase = plants, chitinase = fungi — these three are routinely tested in match-the-following items.
• **Ti plasmid is from Agrobacterium tumefaciens and is for dicot plants; retroviruses are the parallel vector for animal** cells. Don't swap.
• Gel electrophoresis: DNA moves to anode (positive), not cathode — because DNA is negatively charged due to phosphate backbone.
• PCR step order: Denaturation → Annealing → Extension. NTA sometimes reverses annealing and extension as a distractor.