What you need to know
- 8.17–8.22Original mixed practice.
No mark allocations. Numbers are illustrative. No prescribing.
By the end, you should be able to…
- Use restriction endonucleaseAn enzyme that cuts DNA at a specific base sequence, often leaving sticky ends. and ligase in the right order.
- Read a microarrayA slide with thousands of known DNA probes, used to detect which sequences or mRNAs are present in a sample. spot as transcriptionMaking an mRNA copy of a gene, using one strand of DNA as a template, in the nucleus., not as length.
- Pair one benefit with one mechanism of harm.
Build your understanding
Keep the tools in order
Cut with the restriction endonucleaseAn enzyme that cuts DNA at a specific base sequence, often leaving sticky ends., join with ligase, select with the marker, then collect the protein if the gene is expressed. A microarrayA slide with thousands of known DNA probes, used to detect which sequences or mRNAs are present in a sample. asks a different question, about which geneA sequence of DNA bases that codes for a polypeptide or a functional RNA. are already active. bioinformaticsUsing computers to store and analyse biological data, such as DNA and protein sequences. compares the data. Benefits and risks belong to the organism and the trait, not to the word “genetic”.
A short calculation is only arithmetic
If a question says a chip has probes for 12 000 genes and 400 spots are bright in a sample, the fraction active in that snapshot is 400/12000. That is not a mutationA change in the sequence of bases in DNA. rate and not a yield of insulin. Illustrative counts stay labelled as such.
Make your reasoning visible
Order
restriction endonucleaseAn enzyme that cuts DNA at a specific base sequence, often leaving sticky ends. before ligase. mRNA before a claim that a geneA sequence of DNA bases that codes for a polypeptide or a functional RNA. is active.
Both columns
If the question says “evaluate”, write a benefit and a risk with a mechanism.
Avoid this misconception
The claim: A bright spot, a plasmid and a field of maize are one technique.
The correction: They are an expression test, a vector, and a released organism. Each has its own limit.
Check your understanding
Try each question before opening the suggested answer.
Check your understanding (continued)
Practice question
Retrieval and explanation · suggested answer
Name the enzyme that cuts DNA at a recognition site and the enzyme that seals the insert into a plasmid.
Show suggested answer
A restriction endonuclease cuts. DNA ligase seals the sugar-phosphate backbone.
Practice question
Retrieval and explanation · suggested answer
A colony grows on antibiotic agar but does not make the donor protein. Give one reason.
Show suggested answer
The plasmid may have resealed without the insert, or the insert may be present but not transcribed. The marker only shows that the plasmid is there.
Practice question
Retrieval and explanation · suggested answer
400 of 12 000 probes are bright. What fraction of the probed genes look active in this snapshot?
Show suggested answer
400/12000 = 1/30, about 0.033. Bright means mRNA was detected, not that the gene is short or mutant. The count is illustrative.
Practice question
Retrieval and explanation · suggested answer
State one benefit and one risk of a maize plant engineered to make an insect toxin.
Show suggested answer
Benefit: less damage from that insect, so less insecticide may be used against it. Risk: the toxin might harm a non-target insect, or the gene might outcross into a wild relative.
Take the idea further
Apply the same specification knowledge to an unfamiliar problem. Any extra assumptions are supplied in the question.
Stretch question
Illustrative process: plasmids are cut with enzyme E, mixed with a human gene also cut with E, and ligated. Half the mixture is forgotten and not ligated. Both halves are used to transform bacteria and plated on the marker antibiotic. Colonies appear on both plates. Only the ligated plate later yields the human protein. Explain the colonies on the unligated plate, and why the protein appears on only one plate. Assume sticky ends can base-pair but fall apart without ligase, and that a few plasmids were never cut.
Show a hint
A marker does not prove an insert. Unligated ends do not stay joined.
Explore the reasoning
Uncut plasmids still carry the marker, so those bacteria form colonies, but they have no insert and make no human protein. Sticky ends that are not sealed by ligase come apart, so the gene is not stably inside the plasmid. On the ligated plate, some plasmids are sealed with the insert and, where that gene is expressed, the protein can be collected. Colonies alone were never proof of the recombinant product. The “half the mixture” is a teaching story.
Recall this lesson
Lesson recall questions
Question 1 of 5: How do sticky ends produced by a restriction endonuclease allow two DNA molecules to join?
Making recombinant DNA
Practice question
Retrieval and explanation · suggested answer
How do sticky ends produced by a restriction endonuclease allow two DNA molecules to join?
Lesson: 8C 1: Producing Recombinant DNA
Try this from memory first.
Put your biology to work
Explore where these ideas appear in the world. Enrichment, not extra required recall.
Method, product, pattern, judgement
8C · Exam PracticeNHGRI describes recombinant DNA technology, including its use to make proteins such as insulin, and describes microarrays as a way to see genes turned on or off. WHO…Specification 8.18Read & use the scienceClose article
Why this matters
NHGRI describes recombinant DNA technology, including its use to make proteins such as insulin, and describes microarrays as a way to see genes turned on or off. WHO separates a crop-protection benefit from issues such as allergenicity, gene transfer and outcrossing. An exam answer can use that shape: how the DNA was built, what the product is, what a spot means, and one risk with a mechanism. 8.17–8.22 together. A manufactured product or array signal establishes an outcome, but cannot by itself reveal every cloning step or settle every risk.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 8.18 Restriction endonucleases and ligase in recombinant DNA.
Use the science
Which of a bright microarray spot and a sealed recombinant plasmid shows that a gene was already active in a tissue?
Explore a possible response
The bright spot, because it reports mRNA from that tissue. A recombinant plasmid shows that someone joined DNA. It says nothing about what the original tissue was transcribing.
Explore the source
- NHGRI: recombinant DNA technologyUS National Human Genome Research Institute
The same idea made insulin
8C · Producing Recombinant DNAThe NHGRI glossary describes recombinant DNA technology as joining DNA segments, often from different species, and propagating them in bacterial or yeast cells. Its narration says the method…Specification 8.18Read & use the scienceClose article
Why this matters
The NHGRI glossary describes recombinant DNA technology as joining DNA segments, often from different species, and propagating them in bacterial or yeast cells. Its narration says the method has been used to make proteins for treating disease, including insulin and growth hormone. That is the link to the next lesson. This page does not give a dose or a brand protocol. 8.18 and 8.19: cut, join, and insert. Expression of the protein is what turns the method into a product.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 8.18 Restriction endonucleases and ligase in recombinant DNA.
Use the science
Why is “we grew bacteria on antibiotic agar” not yet evidence that human insulin was made?
Explore a possible response
The antibiotic only selects for the marker on the plasmid. Insulin is made only if the insulin gene is present, in a usable orientation, and is transcribed and translated.
Explore the source
- NHGRI: recombinant DNA technologyUS National Human Genome Research Institute