Is it correct to say: Confusing restriction enzymes with DNA polymerase?

Restriction enzymes CUT DNA at specific sequences. DNA polymerase SYNTHESIZES DNA.

Is it correct to say: Writing PCR amplification as arithmetic (N₀ × n)?

PCR is exponential: N = N₀ × 2ⁿ. After 30 cycles ≈ 10⁹-fold increase.

Is it correct to say: Assuming Ti plasmid is used only in animals?

Ti plasmid (Agrobacterium tumefaciens) is used ONLY in dicot plant transformation. Ineffective in animals.

Is it correct to say: Confusing gene cloning with organism cloning?

Gene cloning: multiple copies of a specific DNA fragment. Organism cloning: genetically identical individuals (e.g. Dolly).

Is it correct to say: Writing Bt protein is directly toxic to mammals?

Bt protein needs alkaline pH to activate. Mammalian stomach is acidic — no activation, safe.

Is it correct to say: Not mentioning the primers in PCR?

Primers (short DNA fragments) are essential — they define the region to be amplified.

Formula sheet (PDF) →

Biology · Chapter 12

Biotechnology

Recombinant DNA technology, tools, PCR, applications — Maharashtra HSC Biology Ch 12

10 formulas · 3 solved examples · 5 practice questions · Board weight: 5 marks · Maharashtra State Board Class 12 · 2025–26 syllabus

Board Exam Tips

→Steps of recombinant DNA technology (5 steps: isolation, cutting, ligation, transformation, selection) is a Maharashtra HSC 4-marker.
→Draw a labelled diagram of a Ti plasmid or pBR322 — Balbharati favourite 3-marker.
→PCR (Polymerase Chain Reaction) — 3 stages: denaturation, annealing, extension. Draw thermal profile diagram.
→Applications of biotechnology in agriculture (Bt cotton, golden rice) and medicine (insulin, vaccines) — 3-marker.
→Restriction enzymes with named examples (EcoRI, HindIII, BamHI) — memorise 3-4.

Formulas(10)

Steps of rDNA TechnologyBoard favourite

1) Isolation \to 2) Cutting \to 3) Amplification/Ligation \to 4) Transformation \to 5) Selection

Restriction Endonuclease CuttingBoard favourite

EcoRI: 5’-GAATTC-3’ \to 5’-G + AATTC-3’; makes sticky ends

Vector Requirements

ori, selectable marker, cloning sites, small size

PCR Amplification CycleBoard favourite

Denaturation (94°C) \to Annealing (55°C) \to Extension (72°C)

PCR Amplification Formula

N = N_{0} \times 2^{n}

Bt Toxin GeneBoard favourite

cry1Ac gene from Bacillus thuringiensis \to Bt cotton (bollworm resistance)

Golden Rice

psy gene (daffodil) + crtI (bacteria) \to β-carotene in endosperm

Recombinant InsulinBoard favourite

Human insulin gene \to E . co l i \to humulin

Transgenic Animals

Rosie (transgenic cow) — produces human α-lactalbumin in milk

Gel Electrophoresis

DNA fragments separated by size in agarose gel under electric field

Solved Examples

1Solved Exampleeasy3 steps

Name the enzyme that cuts DNA at a specific sequence and its role in rDNA technology.

Restriction endonucleases are Type II enzymes that recognize palindromic sequences.

Restriction endonucleases (e.g. EcoRI, HindIII, BamHI)

2Solved Exampleboard5 steps

Describe the process of PCR (Polymerase Chain Reaction) with three main steps.

Step 1: Denaturation at 94°C — DNA strands separate.

Denaturation: 94°C, 30s

3Solved ExampleHOTS5 steps

Discuss the process by which Bt cotton was developed and explain how it confers pest resistance.

Bacillus thuringiensis carries the cry1Ac gene coding for Cry protein toxin.

Source: B a c i l l u s t h u r in g i e n s i s

Traps & Common Mistakes

Common Mistakes6

1
Confusing restriction enzymes with DNA polymerase
✓Restriction enzymes CUT DNA at specific sequences. DNA polymerase SYNTHESIZES DNA.
2
Writing PCR amplification as arithmetic (N₀ × n)
✓PCR is exponential: N = N₀ × 2ⁿ. After 30 cycles ≈ 10⁹-fold increase.
3
Assuming Ti plasmid is used only in animals
✓Ti plasmid (Agrobacterium tumefaciens) is used ONLY in dicot plant transformation. Ineffective in animals.
4
Confusing gene cloning with organism cloning
✓Gene cloning: multiple copies of a specific DNA fragment. Organism cloning: genetically identical individuals (e.g. Dolly).
5
Writing Bt protein is directly toxic to mammals
✓Bt protein needs alkaline pH to activate. Mammalian stomach is acidic — no activation, safe.
6
Not mentioning the primers in PCR
✓Primers (short DNA fragments) are essential — they define the region to be amplified.

Practice Yourself

Practice Yourself5 questions

Q1
Name the vector used in gene transfer in dicot plants.
Q2
State two applications of biotechnology in medicine.
Q3
Give the recognition sequence of EcoRI.
Q4
What is the role of DNA ligase in rDNA technology?
Q5
Name the enzyme used in PCR that is heat-stable.

Notes

Biotechnology — Maharashtra HSC Overview

Chapter 12 of the Balbharati Class 12 Biology textbook covers the principles of biotechnology (tools, techniques) and its applications (agriculture, medicine, industry).

Maharashtra syllabus specifics

Five-step process of rDNA technology is asked with specific enzymes and vectors named.
pBR322 and Ti plasmid structures with labelled diagrams are Balbharati-specific 3-markers.
PCR steps and thermal profile — Maharashtra HSC 3-mark diagram-based question.
Bt cotton and golden rice — both cases studies asked with genes and mechanisms.
Human insulin production by rDNA — Maharashtra staple.
Bioethics and biosafety — Balbharati has short section on ethical concerns (GMOs, patenting, biopiracy).

Study tips

Memorise 3-4 restriction enzymes with their recognition sequences and cut patterns.
Draw a clear flowchart of rDNA steps.
For PCR, include primer, dNTPs, Taq polymerase, template DNA, buffer as reagents.
Learn scientific/gene names: cry1Ac, cry2Ab, psy, crtI.
Know the year and name of important discoveries (Watson-Crick 1953, Cohen-Boyer 1972, Dolly 1996).