Explain the tools used in gene transfer
Link restriction enzymes, ligase, plasmids, DNA polymerase and reverse transcriptase to their roles.
A Level; Cambridge International Biology 9700, 2028–2030. This is curriculum teaching, not medical advice or a claim that a treatment is suitable for an individual. Written responses are self-checked
Before you begin
- DNA stores genetic information; genes can be expressed to produce RNA and protein.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What is the role of DNA ligase?
What you will learn
- Explain how restriction endonucleases cut DNA and ligase joins it
- Explain how plasmids, DNA polymerase and reverse transcriptase support transfer
Build the explanation
Restriction endonucleases recognise specific DNA sequences and cut DNA. Compatible ends allow a gene insert to be placed in a vector; DNA ligase joins DNA fragments by forming phosphodiester bonds. A plasmid can carry recombinant DNA into a host. DNA polymerase synthesises DNA using a template, while reverse transcriptase makes DNA from an RNA template.
Use the evidence carefully
The enzymes have different roles: cutting, joining, DNA copying or copying from RNA. A vector carries DNA but does not cut or join it. Enzyme action requires suitable substrates and conditions; the final construct must also be transferred and expressed.
Pause and explain
Why are a plasmid and ligase both useful in a transfer method?
Worked example
A cut donor gene is joined into a cut plasmid. Which enzyme forms the DNA joins?
Show the worked solution
- Restriction enzymes cut DNA.
- Ligase joins DNA fragments.
Answer DNA ligase joins the inserted gene and plasmid DNA.
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Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Which enzyme recognises a sequence and cuts DNA at or near it?
Give me a hint
Identify the relevant material or technology and explain each step.
Compare my reasoning
- The task is cutting a specific DNA sequence.
- Use a restriction endonuclease.
A restriction endonuclease.
Look for these in your work
- Method identified
- Steps linked to function
A sample contains mRNA and a DNA copy is required. Which enzyme is needed?
Give me a hint
Use the stated example to justify a conclusion.
Compare my reasoning
- The template is RNA.
- Use reverse transcriptase.
Reverse transcriptase copies an RNA template into a DNA sequence.
Look for these in your work
- Evidence interpreted
- Limits stated
Why are a plasmid and ligase both useful in a transfer method?
Give me a hint
Apply the idea to a new application or trade-off.
Compare my reasoning
- The plasmid carries the insert.
- Ligase joins the insert to vector DNA.
The plasmid acts as a vector that carries DNA into a host; ligase joins the gene insert to the plasmid.
Look for these in your work
- Application explained
- Claim appropriately bounded
Common mistakes
- Swapping the roles of restriction enzyme and ligase
- Saying reverse transcriptase copies DNA into RNA
What can you explain now?
What is the role of DNA ligase?
Compare with the explanation
Join DNA fragments
It forms bonds in the joined DNA backbone.
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Make it stick
Which tool cuts, joins, carries, copies DNA and copies RNA into DNA?
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