8.2.5
Regulating Transcription
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Transcription Factors
Genes are expressed by transcription and translation. In eukaryotic cells, not all of the genes are expressed in a specialised cell. Gene expression is controlled by transcription factors.

Function
- Transcription factors are proteins that control gene expression by stimulating or inhibiting the transcription of target genes.
- Transcription factors are produced in the cytoplasm and move to the nucleus.
- In the nucleus, transcription factors bind to a specific region of DNA to stimulate or inhibit the gene.

Activators
- Transcription factors that stimulate gene expression are called activators.
- Activators promote the transcription of the genes by interacting with an enzyme called RNA polymerase and allowing it to bind to DNA.

Repressors
- Transcription factors that inhibit gene expression are called repressors.
- Repressors prevent the transcription of genes by stopping RNA polymerase from binding to DNA.
Hormones
Transcription can also be regulated by hormones. There are two types of hormone involved:

Peptide hormones
- Peptide hormones bind to the cell surface membrane and trigger a secondary messenger response.
- The secondary messenger will lead to the activation or inhibition of transcription of some genes.

Lipid-soluble steroid hormones
- Lipid-soluble steroid hormones can pass through the phospholipid membrane.
- Steroid hormones interact directly with DNA to promote or inhibit gene expression.
- E.g. Oestrogen.
Oestrogen
Oestrogen is a lipid-soluble steroid hormone that can enter the cell and directly interact with DNA to initiate gene transcription. The steps involved are:

1) Enter the cell
- Oestrogen enters the cytoplasm of the cell through the cell surface membrane.
- Oestrogen is lipid-soluble so it can pass through the phospholipid bilayer.

2) Bind to transcription factors
- Oestrogen binds to receptors on transcription factors in the cytoplasm.
- Binding of oestrogen causes the transcription factors to change shape.
- The transcription factors form a receptor-hormone complex that can now enter the nucleus.

3) Bind to DNA
- The receptor-hormone complex binds to the promoter region of the DNA.
- Binding to DNA activates transcription.
- This stimulates protein synthesis.
1Biological Molecules
1.1Monomers & Polymers
1.2Carbohydrates
1.3Lipids
1.4Proteins
1.5Nucleic Acids
1.6ATP
1.7Water
1.8Inorganic Ions
2Cells
2.1Cell Structure
2.2Mitosis & Cancer
2.3Transport Across Cell Membrane
2.4Cell Recognition & the Immune System
3Substance Exchange
3.1Surface Area to Volume Ratio
3.2Gas Exchange
3.3Digestion & Absorption
3.4Mass Transport
4Genetic Information & Variation
4.1DNA, Genes & Chromosomes
4.2DNA & Protein Synthesis
4.3Mutations & Meiosis
4.4Genetic Diversity & Adaptation
4.5Species & Taxonomy
4.6Biodiversity Within a Community
4.7Investigating Diversity
5Energy Transfers (A2 only)
5.1Photosynthesis
5.2Respiration
5.3Energy & Ecosystems
6Responding to Change (A2 only)
6.1Nervous Communication
6.2Nervous Coordination
6.3Muscle Contraction
6.4Homeostasis
7Genetics & Ecosystems (A2 only)
7.1Genetics
7.2Populations
7.3Evolution
8The Control of Gene Expression (A2 only)
8.1Mutation
8.2Gene Expression
8.3Genome Projects
Jump to other topics
1Biological Molecules
1.1Monomers & Polymers
1.2Carbohydrates
1.3Lipids
1.4Proteins
1.5Nucleic Acids
1.6ATP
1.7Water
1.8Inorganic Ions
2Cells
2.1Cell Structure
2.2Mitosis & Cancer
2.3Transport Across Cell Membrane
2.4Cell Recognition & the Immune System
3Substance Exchange
3.1Surface Area to Volume Ratio
3.2Gas Exchange
3.3Digestion & Absorption
3.4Mass Transport
4Genetic Information & Variation
4.1DNA, Genes & Chromosomes
4.2DNA & Protein Synthesis
4.3Mutations & Meiosis
4.4Genetic Diversity & Adaptation
4.5Species & Taxonomy
4.6Biodiversity Within a Community
4.7Investigating Diversity
5Energy Transfers (A2 only)
5.1Photosynthesis
5.2Respiration
5.3Energy & Ecosystems
6Responding to Change (A2 only)
6.1Nervous Communication
6.2Nervous Coordination
6.3Muscle Contraction
6.4Homeostasis
7Genetics & Ecosystems (A2 only)
7.1Genetics
7.2Populations
7.3Evolution
8The Control of Gene Expression (A2 only)
8.1Mutation
8.2Gene Expression
8.3Genome Projects
Practice questions on Regulating Transcription
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