Genetic Engineering

    OCR
    GCSE

    Genetic engineering involves the modification of an organism's genome by introducing a gene from another organism to confer a desired characteristic. The process necessitates the use of restriction enzymes to isolate genes and vectors, such as bacterial plasmids or viruses, to transfer genetic material into host cells. Candidates must demonstrate understanding of the specific enzymatic mechanisms, including the role of DNA ligase in forming recombinant DNA, and evaluate the ethical, social, and economic implications of genetically modified organisms (GMOs) in agriculture and medicine.

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    Objectives
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    Exam Tips
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    Pitfalls
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    Key Terms
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    Mark Points

    What You Need to Demonstrate

    Key skills and knowledge for this topic

    • Award 1 mark for stating that restriction enzymes are used to isolate the required gene by cutting DNA at specific base sequences
    • Credit responses that mention the formation of 'sticky ends' on both the donor gene and the plasmid vector to ensure compatibility
    • Award 1 mark for identifying ligase as the enzyme used to join the DNA strands together to form recombinant DNA
    • Candidates must link the use of a vector (plasmid or virus) to the transfer of the gene into the host cell
    • Award 1 mark for explaining that the modified cells are cultured/cloned to produce the required protein (e.g., insulin)

    Example Examiner Feedback

    Real feedback patterns examiners use when marking

    • "You correctly identified the vector, but you need to name the specific enzymes used to cut and join the DNA to secure Higher Tier marks"
    • "Good use of the term 'sticky ends' — ensure you explain that these allow complementary base pairing between the gene and the plasmid"
    • "You listed benefits of GM crops; to access the top band, you must also consider the potential negative impacts on ecosystems or biodiversity"
    • "Be careful not to confuse selective breeding with genetic engineering; remember that genetic engineering involves direct manipulation of DNA in a lab"

    Marking Points

    Key points examiners look for in your answers

    • Award 1 mark for stating that restriction enzymes are used to isolate the required gene by cutting DNA at specific base sequences
    • Credit responses that mention the formation of 'sticky ends' on both the donor gene and the plasmid vector to ensure compatibility
    • Award 1 mark for identifying ligase as the enzyme used to join the DNA strands together to form recombinant DNA
    • Candidates must link the use of a vector (plasmid or virus) to the transfer of the gene into the host cell
    • Award 1 mark for explaining that the modified cells are cultured/cloned to produce the required protein (e.g., insulin)

    Examiner Tips

    Expert advice for maximising your marks

    • 💡When describing the process, use the mnemonic 'Cut, Vector, Join, Insert' to ensure all steps are covered in logical order
    • 💡For 6-mark evaluation questions on GM crops, ensure you provide a balanced argument (e.g., increased yield/nutrition vs. potential reduction in biodiversity or superweeds)
    • 💡Memorize the specific function of ligase: it joins DNA strands, whereas restriction enzymes cut them—this is a frequent discriminator on Higher Tier papers

    Common Mistakes

    Pitfalls to avoid in your exam answers

    • Stating that 'enzymes' cut DNA without specifying 'restriction enzymes' or confusing them with ligase (which joins DNA)
    • Believing that the entire genome is transferred rather than a specific gene responsible for a desired trait
    • Confusing the vector (plasmid) with the host bacterium; failing to describe the plasmid as a carrier mechanism
    • In evaluation questions, listing generic 'bad for the environment' points without specifying mechanisms like cross-pollination with wild relatives

    Key Terminology

    Essential terms to know

    Enzymatic manipulation of DNA (restriction enzymes and ligase)
    Vector-mediated gene transfer (plasmids and viruses)
    Applications in medicine (insulin production) and agriculture (GM crops)
    Ethical, social, and ecological implications of GMOs

    Likely Command Words

    How questions on this topic are typically asked

    Describe
    Explain
    Evaluate
    Suggest
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