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# 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.

Updated Nov 12, 2026

## 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.

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## Connections

## Related conditions 1

- [Sickle cell disease](https://durgical.com/en/conditions/sickle-cell-disease/)

## Related 8

- [Transcription](https://durgical.com/en/biochemistry/topics/transcription/)
- [Epigenetics: DNA and histone methylation](https://durgical.com/en/biochemistry/topics/epigenetics-dna-and-histone-methylation/)
- [The lac operon and gene regulation in bacteria](https://durgical.com/en/biochemistry/topics/the-lac-operon-and-gene-regulation-in-bacteria/)
- [Nuclear receptors](https://durgical.com/en/biochemistry/topics/nuclear-receptors/)
- [RNA processing (cap, poly-A tail and splicing)](https://durgical.com/en/biochemistry/topics/rna-processing/)
- [Dihydrofolate reductase (DHFR)](https://durgical.com/en/biochemistry/enzymes/dihydrofolate-reductase/)
- [Hemoglobin variants (HbA, HbA2, HbF, HbS, HbC)](https://durgical.com/en/biochemistry/topics/hemoglobin-variants/)
- [MicroRNA, RNA interference and antisense drugs](https://durgical.com/en/biochemistry/topics/microrna-rna-interference-and-antisense-drugs/)

Educational information, not medical advice. For any symptom, see a health professional.

Sources: [Can genes be turned on and off in cells?: MedlinePlus Genetics](https://medlineplus.gov/genetics/understanding/howgeneswork/geneonoff/) (MedlinePlus, US National Library of Medicine, 2026); [Gene Regulation](https://www.genome.gov/genetics-glossary/Gene-Regulation) (National Human Genome Research Institute (NHGRI), 2026); [Gene Amplification](https://www.genome.gov/genetics-glossary/Gene-Amplification) (National Human Genome Research Institute (NHGRI), 2026).

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/biochemistry/topics/control-of-gene-expression-in-human-cells/