CBSE Class 12 Biology: Biotechnology Principles — Notes 2026

Tools of Recombinant DNA Technology

• Restriction enzymes (molecular scissors): endonucleases that cut DNA at specific recognition sequences; EcoRI cuts at 5'-GAATTC-3'
• Vectors: carry foreign DNA into host; plasmids (pBR322), bacteriophages, cosmids, BACs, YACs
• Host: cell into which recombinant DNA is introduced; E. coli most common; also yeast, plant, mammalian cells

Restriction Enzymes

• Named after bacterium: Eco = E. coli, R = RY13 strain, I = first enzyme isolated
• Create sticky ends (overhang) or blunt ends; sticky ends allow complementary fragment joining
• Each enzyme cuts only specific palindromic sequence; EcoRI: 5'—G↓AATTC—3' / 3'—CTTAA↑G—5'

Cloning Vectors — Plasmids

• pBR322: contains ampicillin (amp) and tetracycline (tet) resistance genes; ori sequence; restriction sites
• Insertional inactivation: insert foreign DNA into tet gene → tet resistance lost; grow on amp plates → pick white colonies (recombinant)
• Ti plasmid (Agrobacterium tumefaciens): used for plant transformation; T-DNA inserts into plant genome

PCR (Polymerase Chain Reaction)

• Amplifies specific DNA sequence; 3 steps: denaturation (95°C, helix unwinds), annealing (50–60°C, primers bind), extension (72°C, Taq pol extends)
• Taq polymerase: thermostable DNA polymerase from Thermus aquaticus (hot spring bacterium)
• Applications: forensics (crime scene DNA), diagnosing infections (COVID PCR test), genetic testing, cloning

Gel Electrophoresis

• Separates DNA fragments by size; agarose gel; negative DNA moves toward positive electrode
• Smaller fragments: move faster (further); larger: move slower (closer to wells)
• Visualisation: ethidium bromide (EtBr) staining + UV light; bands compare with DNA ladder (known fragment sizes)

Recombinant DNA Technology — Process

• Cut DNA with same restriction enzyme; ligate with DNA ligase; transform into host; select recombinants
• Transformation: heat shock (E. coli) or electroporation; only some cells take up plasmid
• Bioreactors: scale-up recombinant protein production; stirred tank reactors; sterile conditions; monitoring pH, temperature, O₂

CBSE Board Focus

• Biotechnology principles: 5–7 marks; restriction enzymes, PCR, gel electrophoresis mechanism
• Draw: process of recombinant DNA technology as flowchart
• Define: cloning vector; list 3 essential features of a good vector (ori, selectable marker, multiple cloning site)