Different cells can carry the same DNA and still behave like they live in different worlds. If you have ever wondered how a neuron can spend its life firing signals while a muscle cell just wants to contract, you are already asking a core IB Biology question: why do different cells express different subsets of genes?
In IB Biology, the simplest way to say it is: every cell has the full genome, but each cell uses a different “working set” of genes. Those choices shape the cell’s transcriptome and proteome, which is why structure and function diverge so dramatically.
The IB Biology checklist (learn this, then expand)
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Same genome in (almost) all body cells
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Different genes are transcribed in different cell types
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Transcription factors switch genes on/off at promoters and enhancers
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Epigenetic tags (DNA methylation, histone modification) change chromatin accessibility
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Signals (hormones, nutrients, stress) adjust expression in real time
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Stable patterns are maintained through cell division, preserving specialization
For a syllabus-aligned deep dive, keep IB Biology Topic D2.2: Gene Expression open while you revise.
Transcription factors: the decision-makers
A cell becomes “itself” largely by producing a particular combination of transcription factors. These regulatory proteins bind DNA near genes and either recruit RNA polymerase (activation) or block it (repression). In exam terms, you are explaining control of transcription.
If your answers feel vague, anchor them with the language from How Activators & Repressors Control Genes. In IB Biology, markers love seeing words like promoter, enhancer, silencer, and RNA polymerase because they signal mechanism, not just description.
Epigenetics: the “access” layer on top of DNA
Epigenetic modification changes how tightly DNA is packaged without changing base sequence. When chromatin is condensed (heterochromatin), genes are harder to transcribe. When it is open (euchromatin), transcription machinery can access promoters.
Two high-yield examples for IB Biology:
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DNA methylation at promoters usually reduces transcription.
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Histone modification can loosen or tighten nucleosome packing.
These marks help daughter cells “remember” identity after mitosis. That is why your liver stays liver even though it keeps dividing.
Signals and environment: gene expression that reacts
Cells are not isolated. Hormones, nutrients, temperature, and local signalling molecules can shift gene expression to match conditions. Insulin signalling, hypoxia responses, and stress pathways are all examples of cells adjusting their gene expression profile.
To revise this with clean examples, use Regulation of Gene Expression - IB Biology.
Post-transcription control: fine-tuning with microRNAs
Even after transcription, cells can decide how much protein actually gets made. microRNAs bind to target mRNAs and reduce translation or trigger degradation. This is an elegant way to “turn down” a gene without changing transcription.
Revision support: How microRNAs Regulate Gene Expression.
How to turn this into marks (fast)
After you study the mechanism, practise it under pressure. In RevisionDojo, that usually means:
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Use the D2.2 Gene Expression Questionbank (HL) to drill wording and command terms.
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Patch gaps with Notes for D2.2 Gene expression (HL).
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Reinforce definitions with Flashcards for Cell biology - IB.
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When you are ready for full rehearsal, use Biology Predicted Papers (Free) and then circle back to weak areas.
Closing: make gene expression your advantage in IB Biology
Once you see gene expression as a set of layered controls (transcription factors, epigenetics, signals, and RNA regulation), IB Biology questions on specialization stop feeling random. RevisionDojo helps you turn that understanding into exam performance with Study Notes, Flashcards, AI Chat, Grading tools, the Coursework Library, Tutors, Predicted Papers, Mock Exams, and a targeted Questionbank. Start by revising D2.2, practise with timed questions, and let each mistake teach you which “layer” you forgot to explain.