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8.4.3Unit 2: Cells, Development, Biodiversity and Conservation

Transfer of Recombinant DNA into Other Cells — IAL Edexcel Linear Revision Notes & Topical Questions

5 min read 5 parts Lesson 26 of 26 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 5Plasmid Vectors

1
A plasmid, a small circular loop of double-stranded DNA, is cut open by a restriction endonuclease at one site.
2
DNA ligase joins the desired gene into the opening, forming a recombinant plasmid that also carries a marker gene.
3
Bacteria and plasmids are mixed in ice-cold calcium chloride solution and then briefly warmed to about 40 °C to make the membrane permeable.
4
Alternatively, a short electrical pulse called electroporation makes pores in the membrane so that plasmids can enter.
5
Only a small proportion of bacteria take up a plasmid, so the marker gene is used to find the transformed ones.

Part 2 of 5Viral and Liposome Vectors

Viral vector
  • Viral vector Viruses naturally insert their DNA into host cells, so a harmless virus can carry a desired gene into plant, animal or bacterial cells.
Advantage of viruses
  • Advantage of viruses They are good at getting DNA into the nucleus of a cell, where it can be transcribed.
Disadvantage of viruses
  • Disadvantage of viruses Even harmless viruses can trigger an immune response in the patient, which may reduce the success of treatment.
Liposome
  • Liposome A small vesicle bounded by a phospholipid bilayer that can fuse with the cell surface membrane and release the DNA inside.
Gene therapy
  • Gene therapy Both vectors can deliver a healthy allele to cells of patients with genetic diseases such as cystic fibrosis.

Part 3 of 5Physical Methods

Physical Methods
Gene gun
  • Gene gun Tiny gold or tungsten pellets are coated with DNA and fired at cells, and cells that survive may incorporate the new DNA.
Microinjection
  • Microinjection A fine glass micropipette injects DNA directly into a cell, often to create transgenic animals from fertilised eggs.
Use of plants
  • Use of plants Gene guns are useful for plant cells because the thick cell wall otherwise makes uptake of DNA difficult.
Limitation
  • Limitation These methods damage some of the cells they are used on, so the success rate can be low and many cells are lost.

Part 4 of 5Getting Into the Genome

Getting Into the Genome
Incorporation
  • Incorporation Transferred DNA must become part of the host genome to be copied and passed on when cells divide.
Reaching the nucleus
  • Reaching the nucleus In eukaryotic cells very few transferred genes reach the nucleus, which is a barrier to successful gene therapy.
Expression
  • Expression Once in the nucleus, the gene must be transcribed and translated, so it needs the correct control sequences.
MethodTypical hostKey point
PlasmidBacteriaMarker gene needed to find transformed cells
VirusHuman, plant or bacterial cellsReaches the nucleus but may trigger immunity
LiposomeAnimal cellsFuses with the cell surface membrane
Gene gunPlant cellsDNA-coated metal pellets fired in
MicroinjectionZygotes or animal cellsDNA injected through a micropipette

Part 5 of 5Exam Checklist & Tips

8.4.3 – Key Points for the Exam

  • Transformation Uptake and expression of foreign DNA by a cell.
  • Plasmid A small circular DNA molecule found in bacteria, often used as a vector.
  • Liposome A small phospholipid vesicle used to carry DNA into cells.
  • Electroporation Making membrane pores with a brief electric shock so that DNA can enter.
  • Gene therapy Inserting a healthy gene into cells of a patient with a genetic disorder.

Common Mistakes

  • Thinking that all bacteria take up the plasmid;
    • only a small proportion do, which is why marker genes are used.
  • Saying that liposomes are made of protein; they have a phospholipid bilayer, like a cell membrane.
  • Assuming that a transferred gene works immediately;
    • it must reach the nucleus and be incorporated to be expressed.
  • Mixing up the methodsgene guns fire coated pellets, whereas microinjection uses a fine glass needle.

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Cambridge 9700 AS Biology Core Formula

Magnification Triangle & Unit Conversion

Formula: M = I / A  ⇔  A = I / M  ⇔  I = M × A

Units: 1 mm = 1,000 μm = 1,000,000 nm.
Rule: Convert Image size (ruler mm) to μm by ×1,000 before dividing by Actual size.

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