What you need to know
- 8.20–8.22Enrichment on reading a microarrayA slide with thousands of known DNA probes, used to detect which sequences or mRNAs are present in a sample. and a sequence alignment as evidence with limits. Not a drug-design method to memorise.
No invented success rates, no patient data, and no claim that a bright spot is a treatment.
By the end, you should be able to…
- Separate “this geneA sequence of DNA bases that codes for a polypeptide or a functional RNA. is active in the diseased tissue” from “this protein is a safe drug target”.
- Say what a sequence alignment adds.
- State one risk of then making that protein in a released organism rather than in a fermenter.
Build your understanding
A pattern is a hypothesis
Suppose a microarrayA slide with thousands of known DNA probes, used to detect which sequences or mRNAs are present in a sample. shows one geneA sequence of DNA bases that codes for a polypeptide or a functional RNA. much more active in a diseased tissue than in a healthy one. That is evidence of transcriptionMaking an mRNA copy of a gene, using one strand of DNA as a template, in the nucleus., not evidence that blocking the protein would help a person. The gene might be a response to the illness rather than a cause. The next step is a hypothesis.
bioinformaticsUsing computers to store and analyse biological data, such as DNA and protein sequences. can align that protein’s sequence with proteins of known shape. A similar active siteThe region of an enzyme with a specific shape where the substrate binds. might suggest a chemical that could bind it. Similarity is not function until someone tests it. NHGRI’s definition of bioinformatics is storage and analysis of the data. It is not a promise of a medicine.
Where you make it still matters
If the idea survives testing, the protein or the drug might be manufactured in a genetically modifiedHaving DNA that has been changed by genetic engineering, often by adding a gene from another organism. microorganism in a closed fermenter. That is 8.17. Releasing a modified plant that makes the same molecule in a field adds the 8.22 questions: outcrossing, non-target organisms, and whether the trait is still a benefit outside the lab.
Keep the sentences apart. The chip did not design the drug. The alignment did not prove it. The fermenter is not a field.
Make your reasoning visible
Evidence, then the missing test
Say what the spot shows, then say what it cannot show.
Closed versus released
A fermenter and a field do not carry the same ecological risk.
Avoid this misconception
The claim: A geneA sequence of DNA bases that codes for a polypeptide or a functional RNA. that is active in a disease is the cause, and a similar sequence means the drug will work.
The correction: Activity is transcriptionMaking an mRNA copy of a gene, using one strand of DNA as a template, in the nucleus.. Cause and treatment need further tests. An alignment is a clue about similarity, not a clinical result.
Check your understanding
Try each question before opening the suggested answer.
Practice question
Retrieval and explanation · suggested answer
A gene is brighter in diseased tissue on an expression array. What has been shown?
Show suggested answer
That gene was transcribed more in the diseased sample. It has not been shown to cause the disease or to be a safe target.
Practice question
Retrieval and explanation · suggested answer
What can a sequence alignment add?
Show suggested answer
It can show similarity to a protein whose structure or activity is already known, which suggests a hypothesis. It does not prove the new protein behaves the same way.
Practice question
Retrieval and explanation · suggested answer
Why might a fermenter be a lower ecological risk than a field crop for the same product?
Show suggested answer
The microorganism can be contained and the waste sterilised. A field crop can release pollen and the gene can outcross.
Take the idea further
Apply the same specification knowledge to an unfamiliar problem. Any extra assumptions are supplied in the question.
Stretch question
Fictional alignment: a human protein shares 80% of its amino acids with a bacterial enzyme that is blocked by compound X. The human gene is also brighter on a microarray of tumour cells than of healthy cells. A headline says “X cures the tumour”. Write three limits, one from each of 8.20, 8.21 and the need to test. The 80% is illustrative.
Show a hint
Brightness, similarity, and a person are three different claims.
Explore the reasoning
8.20 only shows higher transcription in that sample, not that the protein causes the tumour. 8.21 only shows sequence similarity, and 20% of the amino acids differ, so compound X may not bind the human protein. No experiment here shows that X reaches a tumour, is safe, or changes an outcome. The headline joins those gaps into a cure. The percentage is invented.
Recall this lesson
Lesson recall questions
Question 1 of 5: Describe, in order, how a microarray shows which genes are being transcribed.
Microarrays and active genes
Practice question
Retrieval and explanation · suggested answer
Describe, in order, how a microarray shows which genes are being transcribed.
Lesson: 8C 3: Microarrays and Bioinformatics
Build the sequence from memory first. Then reveal the model order.
Tap the steps in the order you recall. Tap a placed step to send it back.
- 01Next step
- 02Waiting
- 03Waiting
Tap to place
Put your biology to work
Explore where these ideas appear in the world. Enrichment, not extra required recall.
Computers hold the sequences
8C · Thinking BiggerNHGRI describes bioinformatics as using computers to collect, store, analyse and share biological data such as DNA and amino-acid sequences. That is the right size of claim for…Specification 8.21Read & use the scienceClose article
Why this matters
NHGRI describes bioinformatics as using computers to collect, store, analyse and share biological data such as DNA and amino-acid sequences. That is the right size of claim for an alignment. A match in a database is a reason to look again in the laboratory. It is not a finished medicine, and it says nothing about outcrossing if someone later puts the gene into a crop. 8.20–8.22: expression, computing, and the risks of the organism you choose to use.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 8.21 Bioinformatics and biological data.
Use the science
Why is a database match not evidence about pollen?
Explore a possible response
An alignment compares sequences. Pollen and outcrossing are properties of a released plant. The database does not describe that field.
Explore the source
- NHGRI: bioinformaticsUS National Human Genome Research Institute
Turned on, then compared
8C · Microarrays and BioinformaticsThe NHGRI microarray fact sheet says microarrays can study the extent to which certain genes are turned on or off in cells and tissues, by isolating and measuring…Specification 8.21Read & use the scienceClose article
Why this matters
The NHGRI microarray fact sheet says microarrays can study the extent to which certain genes are turned on or off in cells and tissues, by isolating and measuring RNA. That is the expression pattern. Comparing the sequences themselves, at genome scale, is the computing in the bioinformatics glossary and is a separate page from the chip. 8.20 is the active-gene pattern. 8.21 is the computing that makes large sequence and expression data usable.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 8.21 Bioinformatics and biological data.
Use the science
Why can a sequence database not replace the mRNA extraction if the question is which genes are active today in this tissue?
Explore a possible response
The database holds the sequence, which is present whether or not the gene is transcribed. Activity still needs evidence from RNA, which is what the microarray measures.
Explore the source
- NHGRI: DNA microarray technologyUS National Human Genome Research Institute