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8.4.2Unit 6: Practical Skills in Biology II

Recombinant DNA — IAL Edexcel Linear Revision Notes & Topical Questions

5 min read 5 parts Lesson 46 of 48 Unit quiz

📚 IAL Edexcel Linear Hub / Topical Revision
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Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
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Part 1 of 5Why Genes Can Move Between Species

Why Genes Can Move Between Species
Universal code
  • Universal code Almost all organisms use the same four bases and the same codons for the same amino acids, so genes are transferable.
Universal machinery
  • Universal machinery Transcription and translation work in much the same way in all cells, so a transferred gene can still be expressed.
Recombinant DNA
  • Recombinant DNA Joining nucleotide sequences from different sources creates DNA that did not exist naturally in the recipient.
Transgenic organism
  • Transgenic organism An organism containing DNA from another species is transgenic, and is also described as a genetically modified organism.

Part 2 of 5Stages in Producing a Transgenic Organism

1
Identify the gene that codes for the desired characteristic, such as pest resistance in a crop or human insulin.
2
Isolate the gene by cutting it out with restriction endonucleases, by making cDNA from mRNA, or by building a synthetic sequence.
3
Multiply the gene to give many identical copies, using the polymerase chain reaction in a thermocycler.
4
Transfer the gene into the recipient using a vector such as a plasmid, a virus or a liposome, so that the recipient is transformed.
5
Identify transformed cells using a marker gene, then clone these cells so that all new cells carry the gene.

Part 3 of 5Isolating and Joining DNA

Restriction endonuclease
  • Restriction endonuclease An enzyme that cuts DNA only at its own specific base sequence, called a restriction site, such as AAGCTT for HindIII.
Sticky ends
  • Sticky ends An uneven cut leaves short single-stranded overhangs that can form hydrogen bonds with complementary overhangs on other fragments.
Matching cuts
  • Matching cuts Gene and vector must be cut by the same enzyme, so that their sticky ends are complementary and can pair.
DNA ligase
  • DNA ligase This enzyme forms phosphodiester bonds between the sugar-phosphate backbones, permanently joining the gene to the vector DNA.
cDNA
  • cDNA Reverse transcriptase makes DNA from mRNA, giving a gene copy without the non-coding sequences found in the original gene.

Part 4 of 5Copying and Checking

Copying and Checking
PCR
  • PCR A thermocycler uses DNA polymerase, free nucleotides and primers to make a large number of identical copies of the gene.
Marker gene
  • Marker gene A second gene carried with the desired gene, so cells that take up one will also take up the other.
Antibiotic resistance
  • Antibiotic resistance Only transformed cells survive on a medium containing the antibiotic, which allows them to be picked out.
Fluorescence
  • Fluorescence Transformed cells carrying a fluorescent marker glow under ultraviolet light, which makes them easy to identify.

Part 5 of 5Exam Checklist & Tips

8.4.2 – Key Points for the Exam

  • Restriction endonuclease An enzyme that cuts DNA at a specific recognition sequence.
  • Sticky end A single-stranded overhang left by a staggered cut, able to pair with a complementary overhang.
  • DNA ligase An enzyme that joins DNA fragments by forming phosphodiester bonds.
  • cDNA DNA made from an mRNA template by reverse transcriptase.
  • Marker gene A gene used to show which cells have taken up the vector.

Common Mistakes

  • Saying that ligase cuts DNA; restriction enzymes cut, and ligase joins the pieces.
  • Describing sticky ends as double-stranded;
    • they are single-stranded and join by hydrogen bonds between complementary bases.
  • Forgetting that the marker gene is carried on the vector, so it identifies cells that took up the vector.
  • Confusing a vector with the gene; the vector is the carrier and the gene is the cargo.

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  • RNA: 5′ → 3′ 3′ → 5′.
  • : AUG UAC .
  • : UAA, UAG, UGA tRNA (Release Factor) .
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