AQA A-level Biology · 3.8

The control of gene expression

50 revision questions with answers for 3.8 The control of gene expression in AQA A-level Biology (spec 7402). Practise with flashcards, a topic quiz, a random quiz across the course, 5 crosswords, or read every question and answer below.

All 50 questions and answers

Question 1 · Spec 3.8.1 · Mutation types · Recall
Distinguish addition, deletion and substitution of DNA bases.
Answer:
An addition inserts one or more bases. A deletion removes bases. A substitution replaces one base with another. The effect on a protein depends on whether the mutation affects a coding or regulatory region and how it changes the sequence read during expression.
Question 2 · Spec 3.8.1 · Frameshifts · Application
When does an addition or deletion cause a frameshift?
Answer:
Within a coding region, adding or deleting a number of bases that is not a multiple of three shifts the triplet reading frame downstream. Many amino acids may change and a premature stop may appear. Adding or deleting a complete triplet changes length without shifting the downstream frame.
Question 3 · Spec 3.8.1 · Substitution outcomes · Application
How can a substitution have silent, missense or nonsense effects?
Answer:
A silent change specifies the same amino acid because the code is degenerate. A missense change specifies a different amino acid. A nonsense change creates a stop codon, shortening the polypeptide. Use a supplied codon table to determine the actual effect.
Question 4 · Spec 3.8.1 · Other sequence changes · Recall
What are inversion, duplication and translocation of DNA sequences?
Answer:
An inversion reverses a sequence's orientation. A duplication creates an additional copy of a sequence. A translocation moves a sequence to a different position, possibly on another chromosome. Effects depend on changes to genes, regulatory sequences and reading frames.
Question 5 · Spec 3.8.1 · Mutation and function · Application
Why can different mutations in the same gene have very different consequences?
Answer:
Some preserve amino acid sequence, while others alter critical residues, shift the reading frame or affect expression. Changes in bonding can alter protein shape and activity. A mutation's effect also depends on its location, the protein's function and the organism's environment.
Question 6 · Spec 3.8.2.1 · Differential expression · Recall
How can specialised cells have different structures while retaining the same DNA?
Answer:
Different genes are transcribed and translated in different cells. The resulting proteins determine cell structures and activities. Regulatory mechanisms maintain suitable patterns of expression, enabling cells with the same genome to develop distinct specialised functions.
Question 7 · Spec 3.8.2.1 · Totipotency · Recall
What is a totipotent cell, and when does totipotency occur in mammals?
Answer:
A totipotent cell can divide and give rise to every cell type needed to form an organism, including embryonic and extraembryonic tissues. In mammals, totipotency is present only for a limited period during the earliest embryonic stages.
Question 8 · Spec 3.8.2.1 · Stem-cell potency · Recall
Compare pluripotent, multipotent and unipotent cells.
Answer:
Pluripotent cells can produce almost all body cell types. Multipotent cells produce a more restricted range, often within a tissue lineage. Unipotent cells produce one cell type. Stem cells also have the capacity for self-renewal by division.
Question 9 · Spec 3.8.2.1 · Unipotent and iPS cells · Recall
How do the unipotent-cell and induced-pluripotent-cell examples illustrate different developmental capacities?
Answer:
Unipotent cells can produce one specialised cell type, exemplified in the specification by cardiomyocyte formation. Adult somatic cells can be reprogrammed using appropriate transcription factors to produce induced pluripotent stem cells, which can then form a much wider range of cell types.
Question 10 · Spec 3.8.2.1 · Stem-cell therapy · Application
How might stem cells be used to treat a human disorder?
Answer:
Stem cells can be multiplied and induced to differentiate into a required cell type, potentially replacing damaged or missing cells. Successful treatment requires suitable differentiation, integration and function, with control of immune rejection and uncontrolled cell division.
Question 11 · Spec 3.8.2.1 · Stem-cell evaluation · Analysis
What factors should be considered when evaluating stem-cell treatments?
Answer:
Evaluate evidence for effectiveness, long-term safety, tumour risk, immune compatibility and manufacturing consistency. Ethical considerations include the source of cells, embryo use, informed consent, cost and access. Compare treatment claims with controlled clinical evidence.
Question 12 · Spec 3.8.2.2 · Transcription factors · Recall
How do transcription factors control gene expression in eukaryotes?
Answer:
They are proteins that bind specific regulatory DNA sequences and influence transcription. Their movement into the nucleus can stimulate or inhibit target genes by affecting RNA polymerase activity or associated transcription machinery. Different combinations allow cell-specific responses.
Question 13 · Spec 3.8.2.2 · Oestrogen and transcription · Recall
How can oestrogen initiate transcription of a target gene?
Answer:
Oestrogen passes through the cell-surface membrane and binds an intracellular receptor. The resulting complex acts as a transcription factor, enters or acts within the nucleus and binds a specific DNA regulatory sequence, promoting transcription of target genes.
Question 14 · Spec 3.8.2.2 · DNA methylation · Recall
What is epigenetic regulation, and how can increased DNA methylation inhibit transcription?
Answer:
Epigenetic regulation involves heritable changes in gene function without altering DNA base sequence. Increased methylation at relevant regulatory regions can reduce transcription-factor binding or recruit repressive proteins, reducing transcription. Environmental influences can contribute to these changes.
Question 15 · Spec 3.8.2.2 · Histone acetylation · Recall
How can reduced histone acetylation reduce gene expression?
Answer:
Reduced acetylation increases interactions that favour tighter DNA-histone packing. The DNA becomes less accessible to transcription factors and transcription machinery, so transcription can fall. Changes in acetylation can alter expression without changing the DNA base sequence.
Question 16 · Spec 3.8.2.2 · RNA interference · Recall
How can RNA interference inhibit gene expression after transcription?
Answer:
Short RNA molecules associate with a protein complex and guide it to complementary mRNA. The target mRNA can be cleaved or its translation inhibited, reducing production of the encoded protein. Specificity depends on complementary base pairing.
Question 17 · Spec 3.8.2.2 · Expression data · Analysis
A treatment halves target mRNA abundance and reduces its protein. What conclusions are justified?
Answer:
The data are consistent with reduced expression, but do not identify the exact mechanism. Reduced transcription or increased mRNA breakdown could explain the mRNA change. Use controls, normalisation, repeats and additional measurements before assigning a specific regulatory pathway.
Question 18 · Spec 3.8.2.3 · Tumour types · Recall
Distinguish benign and malignant tumours.
Answer:
Benign tumours remain localised and do not invade surrounding tissues or spread to distant sites, although they can still cause harm. Malignant tumours invade tissues and can release cells that spread through blood or lymph, forming secondary tumours.
Question 19 · Spec 3.8.2.3 · Oncogenes · Recall
How can an oncogene promote tumour development?
Answer:
A proto-oncogene normally supports controlled cell growth or division. Mutation or abnormal expression can convert it into an oncogene whose activity drives excessive division or survival. The resulting growth signals may operate without the normal regulatory input.
Question 20 · Spec 3.8.2.3 · Tumour suppressors · Recall
How can loss of tumour-suppressor function contribute to cancer?
Answer:
Tumour-suppressor genes normally help restrain division, repair damage or promote cell death when appropriate. Inactivating mutations or reduced expression remove these controls. Cells with additional abnormalities may then divide uncontrollably and accumulate further changes.
Question 21 · Spec 3.8.2.3 · Epigenetics and cancer · Application
How can abnormal methylation contribute to cancer, and why is this relevant to treatment?
Answer:
Increased methylation can silence a tumour-suppressor gene. Reduced methylation may contribute to inappropriate expression of some growth-promoting genes. Treatments targeting epigenetic regulation may restore aspects of expression, but effects on other genes, cell types and safety must be evaluated.
Question 22 · Spec 3.8.2.3 · Oestrogen and cancer · Application
Why can increased oestrogen exposure promote some breast cancers?
Answer:
In cells with suitable receptors, oestrogen can increase transcription of genes involved in growth and division. More frequent division can support growth of an existing hormone-responsive tumour. Effects depend on receptor status and other genetic and environmental factors.
Question 23 · Spec 3.8.2.3 · Cancer evidence · Analysis
How should an association between an environmental factor and cancer be evaluated?
Answer:
Consider sample size, exposure measurement, confounding factors, absolute risk and reproducibility. A plausible gene-expression or mutation mechanism strengthens interpretation. A correlation by itself cannot establish causation, and different cancers or tumour subtypes may respond differently.
Question 24 · Spec 3.8.3 · Genome projects · Recall
What information can genome sequencing projects provide?
Answer:
They determine DNA base sequences across an organism's genome. Comparisons can identify genes, variants and evolutionary relationships and support investigation of disease. Interpreting biological effects also requires knowledge of regulation, RNA processing and protein function.
Question 25 · Spec 3.8.3 · Predicting the proteome · Application
Why is a complex organism's proteome difficult to predict from its genome alone?
Answer:
Much DNA is non-coding, regulatory interactions affect expression and different cells express different genes. RNA processing can produce different transcripts, and proteins may be modified after translation. Genome sequence therefore does not directly reveal every protein form or its abundance.
Question 26 · Spec 3.8.3 · Genome applications · Application
How can sequencing a simpler organism help identify potential vaccine antigens?
Answer:
Predicted protein sequences can reveal candidate proteins, including proteins likely to be exposed to the immune system. These can be tested for useful antigenic properties. Sequence prediction guides investigation, while experimental evidence is needed to establish protection and safety.
Question 27 · Spec 3.8.4.1 · Recombinant DNA · Recall
What is recombinant DNA and why can a transferred gene be expressed in another species?
Answer:
Recombinant DNA combines DNA sequences from different sources. The genetic code and basic transcription and translation mechanisms are broadly universal. With suitable regulatory sequences and processing requirements, a host can express the introduced gene to produce its polypeptide.
Question 28 · Spec 3.8.4.1 · Obtaining DNA fragments · Recall
What three approaches can produce a desired DNA sequence for genetic engineering?
Answer:
A fragment can be cut from DNA using restriction enzymes, synthesised from an mRNA template using reverse transcriptase, or assembled chemically using a gene machine from a known sequence. Choose an approach suited to the available source and intended host.
Question 29 · Spec 3.8.4.1 · Complementary DNA · Application
How is cDNA made from mRNA, and why is it useful when expressing a eukaryotic gene in bacteria?
Answer:
Reverse transcriptase synthesises DNA complementary to mature mRNA. A second DNA strand can then be made. Because introns have already been removed from mature mRNA, cDNA provides a coding sequence that bacteria can express without eukaryotic RNA splicing.
Question 30 · Spec 3.8.4.1 · Restriction enzymes · Recall
How do restriction endonucleases help produce recombinant DNA?
Answer:
They recognise specific DNA sequences and cut the phosphodiester backbone. Some produce complementary sticky ends. Cutting donor DNA and a vector with the same suitable enzyme can create matching ends that base-pair, positioning the fragments for ligation.
Question 31 · Spec 3.8.4.1 · Vectors and ligase · Recall
How can a plasmid act as a vector, and what does DNA ligase do?
Answer:
A plasmid can carry an inserted DNA fragment into a host cell and be replicated there. Complementary ends hold insert and vector together by base pairing. DNA ligase seals the sugar-phosphate backbone by forming phosphodiester bonds, producing recombinant DNA.
Question 32 · Spec 3.8.4.1 · Regulatory sequences · Recall
Why are promoter and terminator regions added to an introduced gene?
Answer:
A promoter enables host transcription machinery to recognise where transcription should begin. A terminator signals where it should stop. Suitable regulatory sequences are needed for effective expression in the intended host, even when the coding sequence is correct.
Question 33 · Spec 3.8.4.1 · Transformation · Recall
What is transformation in recombinant DNA technology?
Answer:
Transformation is uptake of introduced DNA by a host cell. A suitable method increases entry of a recombinant vector. Because only some exposed cells take up the intended construct, screening or selection is needed before growing an identified transformed population.
Question 34 · Spec 3.8.4.1 · Marker genes · Application
How can marker genes help identify modified cells?
Answer:
A marker creates a detectable characteristic, such as growth under specified selective conditions or a visible signal. Marker arrangements can distinguish cells with a vector and, in suitable designs, those containing an insert. Interpret the supplied design rather than assuming all surviving cells contain the desired gene.
Question 35 · Spec 3.8.4.1 · In vivo amplification · Recall
How can transformed host cells amplify a DNA fragment in vivo?
Answer:
Select a host carrying the desired construct and culture it under controlled conditions. The vector replicates and cell division produces a clone carrying many copies. If the construct is expressed, the host can also produce the encoded protein for extraction and purification.
Question 36 · Spec 3.8.4.1 · PCR requirements · Recall
What components are needed for PCR and what is each one's role?
Answer:
Template DNA contains the target region. Two primers define its boundaries and provide starting points. Free DNA nucleotides supply building units. A thermostable DNA polymerase synthesises new strands. A suitable buffer and ions maintain reaction conditions.
Question 37 · Spec 3.8.4.1 · PCR stages · Recall
Describe one PCR cycle.
Answer:
Heating separates DNA strands. Cooling allows primers to anneal to complementary sequences at opposite ends of the target. Warming to the polymerase's working temperature allows strand extension. Repeating these stages amplifies the target; exact temperatures depend on primers and enzyme.
Question 38 · Spec 3.8.4.1, MS 0.5 · PCR calculation · Calculation
Starting with five target DNA molecules, how many are expected after ten ideal PCR cycles?
Answer:
With perfect doubling, final number = starting number x 2^cycles = 5 x 2¹⁰ = 5120. This is an idealised estimate. Actual amplification may be lower because reaction efficiency declines and reagents become limiting.
Question 39 · Spec 3.8.4.1 · Amplification methods · Recall
Compare in vitro PCR with in vivo amplification in host cells.
Answer:
PCR copies a selected DNA region in a reaction tube using primers and thermal cycling. In vivo amplification uses replication of a vector inside living host cells. Host cells can also express a suitably regulated inserted gene; PCR alone does not produce its protein.
Question 40 · Spec 3.8.4.1 · Applications of recombinant DNA · Application
How can recombinant DNA technology support medicine, industry or agriculture?
Answer:
Hosts can produce useful proteins, including therapeutic proteins or industrial enzymes. Crops can receive genes influencing useful traits. Evaluate each application using the stated benefit, expression system, performance, cost and effects on people and the environment.
Question 41 · Spec 3.8.4.1 · Gene therapy · Application
How can recombinant DNA technology be used in gene therapy?
Answer:
A functional gene copy can be delivered to suitable target cells to restore production of a needed protein. Success depends on delivery, expression level, duration and sufficient treated cells. Risks can include immune responses and harmful disruption of other genes by some delivery methods.
Question 42 · Spec 3.8.4.1 · Evaluating gene technology · Analysis
Which ethical, financial and social issues arise from use and ownership of recombinant DNA technology?
Answer:
Consider health or food-supply benefits, ecological effects, animal welfare, safety evidence, cost and access. Patents and ownership may influence affordability and control of agricultural resources. Assess the specific application and evidence, acknowledging relevant humanitarian concerns and environmental objections.
Question 43 · Spec 3.8.4.2 · DNA probes · Recall
What is a labelled DNA probe and why is its sequence important?
Answer:
A probe is a short, single-stranded DNA sequence carrying a detectable label. It binds by complementary base pairing to a target sequence. Its sequence determines which allele or region it detects, and its label allows the bound probe to be located.
Question 44 · Spec 3.8.4.2 · Hybridisation method · Practical
How can a DNA probe identify a particular allele in a sample?
Answer:
Separate the sample DNA strands, expose them to the labelled probe under suitable conditions, and wash away unbound or weakly bound probe. Detect retained label. A positive signal supports the presence of a complementary target; controls are needed to assess test reliability.
Question 45 · Spec 3.8.4.2 · Genetic screening · Application
How can DNA-based screening inform personalised medicine?
Answer:
Screening can identify alleles associated with inherited conditions, disease risk or drug response. The result can guide monitoring, prevention or treatment choice. Its usefulness depends on test accuracy, the strength of the association and how much environment also influences outcome.
Question 46 · Spec 3.8.4.2 · Genetic counselling · Analysis
What issues should be addressed when discussing a genetic screening result?
Answer:
Explain inheritance, probability, test limitations and available options without treating a risk allele as a guaranteed outcome. Consider informed consent, confidentiality, effects on relatives, anxiety and possible discrimination. Counselling helps individuals make informed choices appropriate to their circumstances.
Question 47 · Spec 3.8.4.3 · VNTRs · Recall
Why are variable number tandem repeats useful in genetic fingerprinting?
Answer:
VNTR regions contain short sequences repeated different numbers of times. Repeat-number differences produce DNA fragments of different lengths. Comparing several variable regions gives a highly discriminating profile because unrelated individuals are unlikely to share the same combination.
Question 48 · Spec 3.8.4.3 · Gel electrophoresis · Practical
How are DNA fragments separated by gel electrophoresis?
Answer:
Load fragments and a size standard into wells in a gel. DNA's negative charge causes movement towards the positive electrode. Smaller fragments usually move further through the gel in a fixed time. Visualise labelled or stained fragments and compare their positions with standards.
Question 49 · Spec 3.8.4.3 · Interpreting fingerprints · Analysis
How are genetic fingerprints used, and what limits an inference from matching bands?
Answer:
Profiles can support forensic identification, parentage analysis and assessment of variation in breeding or populations. At an inherited locus, an offspring's alleles must be accounted for by its parents. A match supports a relationship or shared source; assess the number of loci, chance-match probability and sample quality.
Question 50 · Spec 3.8.1, 3.8.2.2, 3.4.2, 4.2 · Synoptic link · Synoptic
How could an essay link DNA base sequence with phenotype while including regulation and environment?
Answer:
Trace sequence through transcription, RNA processing, translation and protein structure to cell function. Explain how mutations, transcription factors and epigenetic changes alter this pathway. Use examples from different topics to show how environmental conditions interact with gene expression and protein activity to influence phenotype.

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