Recombinant DNA and Gene Transfer · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Cutting pasting and delivering genes

Science · Genetics & Evolution · ages 17-18
Name ______________________   Date ____________

  1. What is a plasmid vector in cloning?

    • A gel that sorts DNA by length
    • A virus that always kills its host
    • A small DNA circle carrying the gene into bacteria

  2. Which jobs do the two cloning enzymes do?

    • Restriction cuts DNA, ligase seals it back up
    • Restriction seals DNA, ligase cuts it open
    • Both enzymes copy RNA back into DNA

  3. Transcription is one of the natural routes of DNA into bacterial cells.

    Circle one:   True   False

  4. Put the cloning steps in the correct order.

    • Isolate DNA, cut with one enzyme, splice with ligase, introduce into hosts
    • Introduce into hosts, isolate DNA, cut, then splice
    • Splice first, then isolate DNA, then cut

  5. Why must the same restriction enzyme cut both the gene and the vector?

    • So both pieces carry matching sticky ends that join
    • So the plasmid turns into a straight chromosome
    • So ligase is destroyed before pasting starts

  6. What is a marker gene for?

    • Cutting the plasmid open at new spots
    • Finding the few successfully altered cells
    • Copying the insulin gene millions of times

  7. Every bacterium mixed with plasmid DNA is assumed to brew insulin. What is wrong?

    • Bacteria can never express human genes
    • Plasmids always kill their host cells
    • Most cells fail, so markers must flag the winners

  8. A student says ligase cuts DNA while restriction enzymes seal it. What is wrong?

    • The roles are swapped: restriction cuts and ligase seals
    • Both enzymes do exactly the same job
    • Neither enzyme touches DNA at all
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Answer key

For grown-ups. Fold this page away before handing over the rest.

Cutting pasting and delivering genes W1-mt_L9yncU_x2P-s1

  1. A small DNA circle carrying the gene into bacteria · The loaded plasmid ferries the gene into the bacterial host cell.
  2. Restriction cuts DNA, ligase seals it back up · Restriction enzymes cut at specific spots and ligase repairs the backbone.
  3. False · The three routes are transformation, transduction and conjugation. Transcription makes RNA.
  4. Isolate DNA, cut with one enzyme, splice with ligase, introduce into hosts · Prepare the pieces, join them, and only then deliver the recombinant plasmid.
  5. So both pieces carry matching sticky ends that join · One enzyme leaves complementary ends on both pieces, which then pair up.
  6. Finding the few successfully altered cells · Most cells fail, so resistance markers let only plasmid holders survive the screen.
  7. Most cells fail, so markers must flag the winners · Uptake and expression succeed rarely, which is why screening with markers matters.
  8. The roles are swapped: restriction cuts and ligase seals · Cutters cut and pasters paste. The student has them backwards.
Worksheet · LightMySky