16.3.2

Transcription Factors

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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.

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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.
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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.
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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:

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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.
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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 an example of a lipid-soluble steroid hormone that can enter the cell and directly interact with DNA to initiate gene transcription. The steps involved are:

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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.
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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.
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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.

Jump to other topics

1Cell Structure

2Biological Molecules

3Enzymes

4Cell Membranes & Transport

5The Mitotic Cell Cycle

6Nucleic Acids & Protein Synthesis

7Transport in Plants

8Transport in Mammals

9Gas Exchange

10Infectious Diseases

11Immunity

12Energy & Respiration (A2 Only)

13Photosynthesis (A2 Only)

14Homeostasis (A2 Only)

15Control & Coordination (A2 Only)

16Inherited Change (A2 Only)

17Selection & Evolution (A2 Only)

18Classification & Conservation (A2 Only)

19Genetic Technology (A2 Only)

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