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LearnYBI11WBI15 · Unit 5: Respiration, Internal Environment, Coordination and Gene TechnologyCoordination, response and gene technologyRecombinant DNA and PCR
Coordination, response and gene technology · Subtopic 2 of 4

Recombinant DNA and PCR

To make recombinant DNA: obtain the gene by restriction enzymes (cut at specific palindromic sites, leaving sticky ends), by reverse transcriptase (mRNA → cDNA, without introns) or by synthesis. Cut a plasmid vector with the same restriction enzyme, so sticky ends are complementary; DNA ligase joins them. Add a promoter so the gene is transcribed. Transform host cells (heat shock with Ca²⁺, electroporation). Identify transformed cells with marker genes (antibiotic resistance, GFP fluorescence). PCR copies DNA: denature at 95 °C, anneal primers at ~55 °C, extend at 72 °C with Taq polymerase; each cycle doubles the DNA (2n2^n). Gel electrophoresis separates DNA fragments by size: DNA (negative phosphates) moves to the anode; smaller fragments travel further.

Cambridge 9700 Paper 4Edexcel YBI11 WBI15AQA 7402 Paper 2≈ 50 minRevision 1 · updated 2026-11-02
Section 1 of 14

Learning objectives

  • Describe the tools of recombinant DNA technology.
  • Describe how a gene is inserted into a plasmid and host.
  • Describe PCR and calculate amplification.
  • Interpret electrophoresis gels.
Pause and think

Why is reverse transcriptase useful for putting a human gene into bacteria?

Section 2 of 14

Core idea

Start hereCut, paste, copy

Biologists cut DNA with enzymes, paste it into bacteria and copy it a billion times in a few hours.

The big idea

Restriction enzymes and ligase build recombinant DNA; PCR amplifies DNA; electrophoresis separates it by size.

Making a GM bacterium

Same enzyme, matching sticky ends.

Worked examplePCR amplification

10 copies, 20 cycles.

Goal
Copies.
Strategy
×2 each cycle.
  1. 220=1 048 5762^{20}=1\,048\,576
    Doubling 20 times.
  2. 10×220≈1.05×10710\times2^{20}\approx1.05\times10^7
    Multiply by starting copies.
AnswerAbout 10.5 million.
✓ CheckReal yields are lower ✓.

Summary

  • Restriction, ligase, vectors.
  • PCR 95/55/72 °C.
  • Small fragments travel furthest.
Key words
Sticky ends
Single-stranded overhangs left by some restriction enzymes.
Vector
DNA molecule that carries a gene into a host cell.
HistoryFirst recombinant DNA. In 1973 Stanley Cohen and Herbert Boyer inserted a gene into a bacterial plasmid, launching the biotechnology industry.
Fun factHot spring enzyme. Taq polymerase comes from Thermus aquaticus, a bacterium found in Yellowstone hot springs.
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