Control of gene expression in human cells
Every cell has the same genes; what makes a liver cell different from a neuron is which genes are on, when, and how strongly.
Key facts
- Most control acts on transcription: the promoter (where RNA polymerase starts), distant enhancers and silencers, and the transcription factors that bind them.
- Response elements let hormones switch genes: steroid and thyroid hormone receptors bind DNA directly; cAMP acts through the factor CREB.
- Chromatin decides access: acetylated histones and unmethylated promoters are open and active; methylated DNA and compact chromatin stay silent.
- After transcription, alternative splicing, mRNA stability, microRNAs and control of translation add further layers.
- Bacteria group genes in operons (the lac operon); human genes are mostly regulated one by one, combining many signals.
In detail
- Gene amplification: extra copies of a gene raise its product; tumours amplify oncogenes (HER2, MYC) and can amplify DHFR to resist methotrexate.
- Developmental switching: the haemoglobin genes change from embryonic to fetal (HbF) and then to adult (HbA) forms.
- Tissue-specific genes need tissue-specific transcription factors, so the same hormone can switch different genes in different cells.
- Genomic imprinting and X inactivation are forms of silencing by methylation that are kept when cells divide.
- Enzyme induction and repression: a substrate, hormone or drug can raise the amount of an enzyme (PEPCK by cortisol and glucagon, liver CYP enzymes by some drugs).
- Also called
- Gene regulation, Transcription factors and enhancers
Clinical notes
- Drugs that induce liver enzymes (rifampicin, carbamazepine, phenytoin) speed the breakdown of other drugs: a common interaction.
- HER2 amplification in breast cancer is tested because it predicts response to anti-HER2 treatment.
- Hydroxyurea raises fetal haemoglobin, which reduces sickling in sickle cell disease.
Test yourself
Think of the answer, then tap the question to see it.
Why does a liver cell express different genes from a neuron with the same DNA?
Each tissue has its own transcription factors, chromatin state and signals, which switch on a different set of genes.
How can a tumour resist methotrexate through gene amplification?
It makes many copies of the DHFR gene and so much enzyme that the drug can no longer block it.
How do steroid hormones change gene expression?
They bind an intracellular receptor that attaches to a hormone response element in DNA and turns specific genes on or off.
Connections
Educational information, not medical advice. For any symptom, see a health professional.
Sources: Can genes be turned on and off in cells?: MedlinePlus Genetics (MedlinePlus, US National Library of Medicine, 2026); Gene Regulation (National Human Genome Research Institute (NHGRI), 2026); Gene Amplification (National Human Genome Research Institute (NHGRI), 2026).
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Representative model, for educational purposes only.