AQA · A-Level · Biology
Course version: 7402 · Version from Sept 2016
The culture of transformed host cells as an in vivo method to amplify DNA…
Full specification wording
Recombinant DNA technology (A-level only): The culture of transformed host cells as an in vivo method to amplify DNA fragments.
In vivo amplification uses living cells to copy DNA.
Checked against the AQA 7402 specification (opens in a new tab) on .
- Point 6 of 10
Study notes
From the checked teaching notes for this specification point.
The idea
In vivo amplification uses living cells to copy DNA. Recombinant plasmids are mixed with host cells under conditions encouraging uptake, like calcium ions and heat shock. Cells taking up a plasmid are 'transformed'. Since few cells succeed and some plasmids reseal empty, marker genes are used. A primary marker (e.g. antibiotic resistance) identifies cells taking up any plasmid. A secondary marker identifies cells with recombinant plasmids via insertional inactivation. Identified cells are cultured with suitable nutrients and temperature. As bacteria divide by binary fission, the plasmid replicates, amplifying the DNA. Added promoter regions allow protein harvesting.
What earns the marks
- The vector being taken up by host cells, which are then described as transformed.
- A primary marker gene identifying cells that have successfully taken up a plasmid.
- A secondary marker gene identifying recombinant plasmids via insertional inactivation.
- Culturing only the transformed cells under suitable conditions of nutrients, temperature, pH and oxygen.
- The plasmid being copied each time the cell divides by binary fission, increasing fragment copies.
- The protein also being produced, because promoter and terminator regions were added to the fragment.
Common mistakes and how to put them right
Assuming every host cell takes up the vector.
Put it right: Describe the selection step using marker genes.
Saying the bacteria copy the plasmid by mitosis.
Put it right: State that prokaryotes divide by binary fission.
Stating a single marker gene confirms the target DNA is present.
Put it right: A single marker only confirms plasmid uptake, a second marker (insertional inactivation) is needed to confirm the insert.
Writing 'grown in a fermenter' with no conditions named.
Put it right: Specify conditions like suitable temperature, pH and nutrients.
Exam tips
- Mention the selection step; an answer that jumps straight from transformation to culture misses an easy mark.
- Say binary fission, not mitosis, whenever bacterial division is involved.
- Distinguish between primary markers for plasmid uptake and secondary markers for identifying recombinant plasmids.
Try the lesson
The start of the Recombinant DNA technology (A-level only): The culture of transformed host cells as an in vivo method to amplify DNA fragments. lesson, made from checked teaching notes for this specification point.
Have a go first
In the in vivo method of amplifying DNA, what is a transformed host cell?
Listen
In vivo amplification uses living cells to copy DNA. Recombinant plasmids are mixed with host cells under conditions encouraging uptake, like calcium ions and heat shock. Cells taking up a plasmid are 'transformed'. Since few cells succeed and some plasmids reseal empty, marker genes are used. A primary marker (e.g. antibiotic resistance) identifies cells taking up any plasmid. A secondary marker identifies cells with recombinant plasmids via insertional inactivation. Identified cells are cultured with suitable nutrients and temperature. As bacteria divide by binary fission, the plasmid replicates, amplifying the DNA. Added promoter regions allow protein harvesting. A strong answer earns marks for these points. the vector being taken up by host cells, which are then described as transformed. a primary marker gene identifying cells that have successfully taken up a plasmid. a secondary marker gene identifying recombinant plasmids via insertional inactivation. culturing only the transformed cells under suitable conditions of nutrients, temperature, pH and oxygen. A common slip: assuming every host cell takes up the vector. Instead, describe the selection step using marker genes. Exam tip: Mention the selection step; an answer that jumps straight from transformation to culture misses an easy mark.
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