3.8.3 sits at the boundary between the molecular biology of the rest of 3.8 and the question of what to do with the data — what a sequenced genome tells you, what it does not, and what follows when an individual's genome becomes information other parties might want to read.
The genome is all the DNA in a cell; the proteome is what gets made from it.
The genome is constant across the cells of one organism; the proteome is not. Every cell carries the same DNA, but only a fraction of genes are transcribed in any given cell at any moment. The proteome is therefore a functional snapshot of one cell type at one moment, not a direct read-out of the genome.
The genome is all the DNA in a cell or organism. The cell-or-organism qualifier is the credited element.
Write
all the DNA in a cell or organism. AQA rejectsall the DNA in a species,all the genes in a chromosome, andall the genetic material of a species. The qualifier ties the genome to a single biological unit, not to a taxonomic group or to a structural subset.
Selective gene expression (covered in 3.8.2). Different cell types transcribe different subsets of the same genome and therefore produce different proteomes. The proteome also shifts with developmental stage and with environmental conditions; the genome does not.
Differences between organisms of the same species are differences in alleles, not in genes. Same species share the same set of genes; what varies between them is the base sequence at particular loci — the alleles those individuals carry.
The genome predicts the proteome in simple organisms; in complex organisms it does not.
One use of sequencing data is predicting the amino acid sequence of every protein an organism can make, directly from the base sequences in its genome. How reliably this works depends on the organism's complexity.
Predictability of the proteome from the genome.
| Organism | Why prediction works (or doesn't) | Practical consequence |
|---|---|---|
| Simple (bacteria, simple eukaryotes) | Little non-coding DNA; close-to-one-protein-per-gene relationship | Sequencing a pathogen's genome reliably identifies its proteins, supporting vaccine antigen design |
| Complex (humans, other eukaryotes) | Large non-coding fraction; regulatory sequences; one gene can give multiple protein variants | Genome alone does not fully predict the proteome — you also need expression and modification data |
The credited explanation for the complex-organism gap is
non-coding DNAandregulatory sequences. Vague references tocomplicatedormore advancedare not credited; AQA wants the molecular reason named.
Sequencing data supports several applications: comparison, screening, and vaccine design.
The Human Genome Project determined the complete base sequence of the human genome. Comparable projects have sequenced the genomes of many other organisms. The data supports applications in evolutionary comparison, personalised medicine, genetic screening, and vaccine antigen identification.
Comparative genomics: between species (evolutionary relationships) and between individuals (disease-risk alleles, personalised medicine). Genetic screening: carrier status, pre-implantation diagnosis, predictive screening for late-onset conditions such as Huntington's disease and cancer-risk alleles such as BRCA1. Synthetic biology: designing DNA sequences to produce specific proteins for industrial or medical use.
- The pathogen's genome lets scientists identify the proteins it can produce — the pathogen's proteome.
- Those proteins are screened to identify potential antigens the immune system can be trained against.
Write the two steps separately. The genome lets scientists identify proteins; those proteins are screened for antigens. Collapsing the two into "the genome lets scientists make a vaccine" earns one mark, not two.
Vaccines contain antigens, not antibodies. Antibodies are produced by the host in response to the antigen.
PCR, gel electrophoresis, DNA sequencing, genetic fingerprinting, DNA hybridisation, autoradiography. The mechanism of each is examined in 3.8.4; in 3.8.3 questions the requirement is naming two valid items from this list. DNA probes alone is rejected as too vague.
AQA rejects
compare mRNA sequencesandcompare amino acid sequencesas substitutes forcompare DNA sequences. DNA techniques operate at the DNA level.Compare DNA sequenceis accepted as a substitute for DNA sequencing in the name-two-techniques list.
Access to genome data raises ethical questions about discrimination, privacy, and consent.
Sequencing an individual's genome produces information that carries weight beyond medical care. AQA expects students to recognise three categories of ethical concern: discrimination by third parties (employers, insurers); privacy and ownership of genetic data, which describes biological relatives as well as the individual; and the psychological impact of predictive information for which informed consent has special weight.
- State at least one For point, anchored to a specific number or detail from the question stem.
- State at least one Against point, also anchored to a specific number or detail from the stem.
- State a conclusion that follows from the points raised.
A one-sided Evaluate answer is capped at 2 marks regardless of length. The third mark unlocks only when both For and Against are present, each anchored to data from the question.
AQA rejects rote phrases that engage no specific data.
No statistics test,could be cured if caught early(when the stem says no cure exists), andno point screening if they will die anywayall score zero. Each point has to engage the specific clinical and statistical situation the question describes.
Carriers are not a reason against screening. Even when an affected individual dies young, carriers do not die from the condition and continue to reproduce, so identifying carriers justifies a screening programme even for rapidly fatal conditions.
Key terms
- genome
- proteome
- pcr
- electrophoresis
- hybridisation
- genetic material
- personalised medicine
- antigen