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Gene Cloning

CBSE · Class 12 · Biotechnology

Quick revision notes for Gene Cloning — CBSE Class 12 Biotechnology. Key concepts, formulas, and definitions for last-minute revision.

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A diagram illustrating the concept of insertional inactivation using a chromogenic substrate, where insertion of foreign DNA into a gene (e.g., β-galactosidase) inactivates it, leading to a visible ch
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Key Topics to Revise

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3.1 Identification of Candidate Gene

  • The first and most formidable step in gene cloning is identifying the candidate gene of interest.
  • Candidate genes are identified based on their biomedical, economic, or evolutionary significance.
  • Examples: Insulin gene (diabetes), iron-uptake gene (chlorosis), salinity-tolerance gene, milk protein genes, blood-clotting factor genes.
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3.2 Isolation of Nucleic Acids

  • Two major challenges: (i) Nucleic acids are present in very small amounts compared to proteins, carbohydrates and lipids; (ii) Large size of DNA makes it susceptible to cleavage under physical stress.
  • Four steps in nucleic acid extraction: (1) Cell disruption/lysis, (2) Protection from degrading nucleases, (3) Separation from other molecules, (4) Precipitation and concentration using ethanol or iso
  • Bacterial cells: Lysozyme digests peptidoglycan cell wall; SDS (anionic detergent) lyses cell membrane.
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3.3 Enzymes Used for Recombinant DNA Technology

  • Enzymes are the 'molecular scissors and glue' of rDNA technology.
  • NUCLEASES: Cleave nucleic acids by hydrolysing phosphodiester bonds. Types: (i) Exonucleases — remove mononucleotides from 3′ or 5′ ends; (ii) Endonucleases — cleave internal phosphodiester bonds with
  • RESTRICTION ENDONUCLEASES (REs): Endonucleases that recognise and cleave at specific palindromic sequences (4–8 bp). Mostly found in bacteria and archaea as defence against bacteriophages.
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3.4 Modes of DNA Transfer

  • Transfer of foreign DNA into a host cell is a key step in rDNA technology.
  • NATURAL METHODS in bacteria: (i) Transformation, (ii) Transduction, (iii) Conjugation.
  • TRANSFORMATION: Direct uptake of exogenous DNA from surroundings through the cell membrane; recipient cells are called transformants. Occurs naturally in some bacteria.

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Full Notes

Key Concepts

A candidate gene is a geneIsolation of DNA and RNA involvesRestriction enzymes are bacterial/archaeal defense enzymesDNA ligase joins two DNA strandsSeveral other enzymes are critical

Frequently Asked Questions

What are the important topics in Gene Cloning for CBSE Class 12 Biotechnology?
Key topics in Gene Cloning include Gene Cloning — Chapter Overview, Gene Cloning — Complete Chapter Overview, Gene Cloning — Chapter Overview. These are the concepts CBSE Class 12 examiners draw on most — study them first, then practise related questions.
How to score full marks in Gene Cloning — CBSE Class 12 Biotechnology?
Start by understanding all key concepts. Practise previous year questions from this chapter. Revise formulas and definitions regularly. Use flashcards for quick revision before the exam.

Sources & Official References

Content is aligned to the official syllabus. Refer to the board website for the latest curriculum.

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