Recombinant DNA

What It Is

"Isolation and manipulation of DNA, including end-to-end joining of sequences from very different sources to make chimeric molecules (e.g., molecules containing both human and bacterial DNA sequences) is the essence of recombinant DNA research."

• Harper's Illustrated Biochemistry, p. 456

Core Tools and Components

1. Restriction Enzymes (Restriction Endonucleases)

• Naming: Named after their source organism. EcoRI comes from Escherichia coli strain R; BamHI from Bacillus amyloliquefaciens.
• Sticky ends vs. blunt ends: Some enzymes (like BamHI) leave short single-stranded overhangs called "sticky ends" - these are especially useful because complementary sticky ends from two different DNA fragments can anneal and be joined.
• A 4-bp cutter statistically cuts once every 256 bp (4⁴); a 6-bp cutter once every 4,096 bp (4⁶).

2. DNA Ligase

3. Vectors (Cloning Vehicles)

4. Host Cells

The Basic Steps of Recombinant DNA Technology

1. Isolate DNA of interest (from any organism)
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2. Cut with restriction enzyme (creates fragments with sticky ends)
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3. Cut vector with same restriction enzyme
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4. Mix fragments + vector → sticky ends anneal
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5. Seal with DNA ligase → recombinant plasmid formed
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6. Transform into host cells (e.g., E. coli)
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7. Select colonies that carry the recombinant plasmid
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8. Amplify (grow colonies) → large amounts of recombinant DNA
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9. (Optional) Express the gene → recombinant protein produced

Key Supporting Techniques

Polymerase Chain Reaction (PCR)

Gel Electrophoresis

DNA Probes and Hybridization

cDNA (Complementary DNA)

DNA Libraries

• Genomic library: All DNA fragments from an organism's genome, cloned into vectors.
• cDNA library: Copies of all mRNAs expressed by a tissue - reflects which genes are active.

Expression Vectors

Screening Recombinant Clones

• Antibiotic selection: If insert disrupts an antibiotic resistance gene (as in pBR322's ampicillin gene after PstI insertion), bacteria with recombinant plasmids won't grow on ampicillin plates.
• Blue-white screening: If insert disrupts the lacZ gene (β-galactosidase), colonies with inserts are white; unmodified plasmids produce blue colonies on media containing the dye X-gal.

Medical and Practical Applications

"Recombinant DNA techniques provide human insulin for the treatment of diabetes, factor VIII for the treatment of hemophilia, and vaccines for the prevention of hepatitis."

• Basic Medical Biochemistry, p. 542

Modern Extensions

• CRISPR/Cas9: A newer, more precise genome editing system derived from bacterial immunity. Can repair, replace, or knock out specific genes with much higher accuracy than earlier rDNA methods.
• siRNA (small interfering RNA): Silences gene expression post-transcriptionally.
• Next-generation sequencing (NGS): Allows rapid sequencing of entire genomes and cDNA libraries to detect mutations and changes in gene expression.
• Synthetic biology: The cost of synthesizing DNA has dropped so dramatically that entire genes - even small genomes - can now be synthesized from scratch, bypassing the need to clone from natural sources.

Summary

• Harper's Illustrated Biochemistry, 32nd Ed., Chapter 39
• Basic Medical Biochemistry - A Clinical Approach, 6th Ed., Chapter on Molecular Biology Techniques

IISER IAT 2026 - Important PYQs & High-Weightage Topics

Exam Overview

• Format: 60 MCQs - 15 per subject (Physics, Chemistry, Biology, Mathematics)
• Marking: +4 correct, -1 wrong, 0 unattempted
• Duration: 3 hours
• Difficulty: Above JEE Mains, slightly below JEE Advanced - deep conceptual understanding required

🔬 BIOLOGY (15 Questions)

High-Weightage Chapters (appear EVERY year)

Representative PYQ-style Questions

⚗️ CHEMISTRY (15 Questions)

High-Weightage Chapters

Representative PYQ-style Questions

Hint: This requires summing reversible/irreversible work for each step separately.

⚡ PHYSICS (15 Questions)

High-Weightage Chapters

Representative PYQ-style Questions

📐 MATHEMATICS (15 Questions)

High-Weightage Chapters

Representative PYQ-style Questions

Where to Get Official PYQ PDFs

• Official papers (2017-2025): crisprlearning.com/iat-previous-year-questions - has question papers + solutions + analysis
• Chapter-wise practice: questions.examside.com/past-years/jee/iat-iiser - filter by chapter
• Weightage analysis: sciastra.com/blogs/iat-important-topics-chapter-wise-weightage

Key Tips for IAT 2026

1. Biology is the differentiator - most students from JEE background are weak here. Human and Plant Physiology alone can give you 5-6 marks.
2. Chemistry organics, especially carbonyl compounds, have historically carried the most weight (up to 5 Qs in some years).
3. Physics rotation problems appear every year with increasing depth - practice moment of inertia combinations.
4. Math - Functions, Matrices, and Probability have appeared every single year without exception since 2020. Never skip these.
5. Solve last 5-6 years of official papers under timed conditions - exact questions don't repeat but concept patterns do.

IISER IAT - 15 Important PYQs with Solutions (All Subjects)

🔬 BIOLOGY (15 PYQs)

• AaBb (A_B_) - dominant both
• Aabb (A_bb) - dominant A only
• aaBb (aaB_) - dominant B only
• aabb (aabb) - recessive both

• Template 3'-TACGATCG-5'
• mRNA 5'-AUGCUAGC-3' So mRNA = 5'-AUGCUAGC-3' (U replaces T in RNA).

• Glucagon: promotes glycogenolysis and gluconeogenesis (raises blood sugar) - (A) is wrong
• Insulin: promotes glycogenesis and inhibits glycogenolysis (lowers blood sugar) - (B) is wrong
• Cortisol: is a stress hormone that promotes gluconeogenesis (formation of glucose from non-carbohydrate sources) - CORRECT
• Epinephrine: promotes glycogenolysis (breaks down glycogen) - (D) is wrong

• Color blindness is X-linked recessive (gene: X^b)
• Father was color blind: X^b Y → passes X^b to all daughters
• Woman's genotype: received X^b from father + X^b or X^B from carrier mother
• Woman's possible genotypes: X^b X^b (color blind) or X^b X^B (carrier) → equal probability
• But the woman is stated to have normal vision, so she must be a carrier: X^B X^b
• Normal husband: X^B Y
• Cross: X^B X^b × X^B Y
• Sons: X^B Y (normal) or X^b Y (color blind) → 1/2 sons are color blind

• Generation 0: ¹⁵N/¹⁵N (heavy) - 2 molecules
• Generation 1 (in ¹⁴N): ¹⁵N/¹⁴N hybrid - 2 molecules
• Generation 2 (in ¹⁴N): each hybrid molecule replicates → one ¹⁵N/¹⁴N hybrid + one ¹⁴N/¹⁴N light
• Total after 2 generations: 2 hybrid + 2 light = 1:1 ratio of hybrid to light
• This proved semi-conservative replication.

• (A) Rhizobium-legume: mutualism (both benefit - bacteria get shelter, plant gets fixed nitrogen)
• (B) Barnacles on whale: commensalism - barnacles get transport and feeding opportunities (+), whale is unaffected (0)
• (C) Mycorrhizae: mutualism (fungus gets sugars, plant gets minerals)
• (D) Cuckoo-sparrow: brood parasitism (cuckoo benefits, sparrow is harmed)

⚗️ CHEMISTRY (15 PYQs)

• Exothermic reaction: ΔH < 0 (negative)
• Products have 2 moles of gas from 2 moles of solid: ΔS > 0 (positive - disorder increases)
• ΔG = (negative) - T(positive) = always negative at all temperatures
• ΔG < 0 at all temperatures → spontaneous always.

• At C₁=10⁻⁴: 149.1 = Λ°m - A(0.01) ... (1)
• At C₂=9×10⁻⁴: 147.1 = Λ°m - A(0.03) ... (2)
• Subtract: 2.0 = A(0.02) → A = 100
• From (1): Λ°m = 149.1 + 1.0 = 150.1 S·cm²·mol⁻¹

• Xe has 8 valence electrons, forms 4 bonds with F → 4 bonding pairs
• Remaining: 8 - 4×2 = 0 ... wait: Xe uses 4 electrons for bonds, remaining = 8 - 4 = 4 electrons = 2 lone pairs
• Total electron pairs = 4 bond + 2 lone = 6 → sp³d² hybridization
• 6 electron pairs = octahedral arrangement of electrons
• 2 lone pairs go to opposite axial positions (minimizing repulsion)
• Result: square planar geometry (4 F atoms in a plane, 2 lone pairs above and below)

• After 10 min (1 t₁/₂): N = N₀/2
• After 20 min (2 t₁/₂): N = N₀/4
• After 30 min (3 t₁/₂): N = N₀/8
• After 40 min (4 t₁/₂): N = N₀/16

• Fe (Z=26): [Ar] 3d⁶ 4s²
• Fe²⁺: loses 4s² → 3d⁶ → using Hund's rule: ↑↓ ↑ ↑ ↑ ↑ → 4 unpaired
• Fe³⁺: loses 4s² and one 3d → 3d⁵ → ↑ ↑ ↑ ↑ ↑ → 5 unpaired ← maximum
• Cu²⁺: [Ar]3d⁹ → 1 unpaired
• Zn²⁺: [Ar]3d¹⁰ → 0 unpaired

• HClO (Cl in +1): weakest acid
• HClO₄ (Cl in +7): strongest acid (perchloric acid is one of the strongest acids known)

• C1: COOH
• C2: CH₂
• C3: CH(OH) ← OH substituent here
• C4: CH₃

• n = 2
• F = 96500 C/mol
• E° = +0.46 V

• en (ethylenediamine) is a bidentate ligand (donates 2 donor atoms)
• 2 en ligands donate = 4 coordination positions
• 2 Cl⁻ inside the bracket donate = 2 coordination positions
• Coordination number = 4 + 2 = 6
• Charge balance: Co + 2(0) + 2(-1) + (-1 outside) = 0 → Co = +3
• Oxidation state of Co = +3

• (A) Free radical substitution
• (B) Electrophilic addition (alkene)
• (C) CH₃CHO + HCN: CN⁻ acts as a nucleophile and attacks the electrophilic carbonyl carbon (C=O) of acetaldehyde. The CN⁻ donates its electron pair to C, forming a tetrahedral intermediate. This is classic nucleophilic addition to a carbonyl compound, giving a cyanohydrin.
• (D) Electrophilic aromatic substitution

• Ideal gas assumes no intermolecular forces and zero molecular volume.
• In real gases, molecules attract each other, which reduces the pressure they exert on walls → the measured P is lower than ideal → add a/V² correction (a = measure of intermolecular attraction strength)
• Real gas molecules have finite size, so not all of V is available for movement → subtract b (excluded volume per mole, related to molecular radius: b ≈ 4 × N_A × volume of one molecule)

• Dilute H₂SO₄ dissociates: H₂SO₄ → 2H⁺ + SO₄²⁻
• At cathode (reduction): H⁺ ions are reduced → 2H⁺ + 2e⁻ → H₂
• At anode (oxidation): Water is oxidized (SO₄²⁻ is a poor oxidizing agent in dilute solution) → 2H₂O → O₂ + 4H⁺ + 4e⁻
• Volume ratio H₂:O₂ = 2:1 (from stoichiometry)

• HCl, HBr, HI: boiling point increases with molecular mass (London dispersion forces increase) → HCl < HBr < HI
• HF has the highest BP despite being the lightest, because it forms strong hydrogen bonds (F is the most electronegative element) which require more energy to break.
• Final order: HCl (-85°C) < HBr (-67°C) < HI (-35°C) < HF (+19.5°C)

⚡ PHYSICS (15 PYQs)

• sin²(ωt) = (1 - cos2ωt)/2
• cos³(ωt) = (3cosωt + cos3ωt)/4

• Kinetic energy gained: KE = eV (e = charge, V = potential difference)
• KE = p²/2m → p = √(2m·eV)
• de Broglie wavelength: λ = h/p = h/√(2meV)

• λ_α = h/√(2·4m_p·2e·V) = h/√(16m_p·e·V)
• λ_p = h/√(2·m_p·e·V)

• New length L' = 2L
• Volume is conserved: A·L = A'·2L → A' = A/2
• New resistance: R' = ρ(2L)/(A/2) = ρ·4L/A = 4R

• Solid sphere about diameter: I = 2MR²/5
• Hollow sphere about diameter: I = 2MR²/3
• Solid cylinder about axis: I = MR²/2
• Ring about axis: I = MR²
• Rod about center: I = ML²/12

📐 MATHEMATICS (15 PYQs)

• Injective: f(x) = f(y) → 10x = 10y → x = y ✓
• Surjective: For any b ∈ ℚ, f(b/10) = 10·(b/10) = b ✓ (b/10 ∈ ℚ since ℚ closed under division)
• Therefore f is bijective.

• nth term: aₙ = Sₙ - Sₙ₋₁ = (3n² + 5n) - [3(n-1)² + 5(n-1)]
• = 3n² + 5n - 3(n² - 2n + 1) - 5(n-1)
• = 3n² + 5n - 3n² + 6n - 3 - 5n + 5
• = 6n + 2

• At x = 2: y = 8 - 6 = 2. Point = (2, 2)
• Slope = dy/dx = 3x² - 3. At x=2: slope = 3(4) - 3 = 9
• Tangent: y - 2 = 9(x - 2) → y = 9x - 18 + 2 = y = 9x - 16

• Trace = sum of diagonal elements = 1 + 4 = 5
• Determinant = (1)(4) - (2)(3) = 4 - 6 = -2