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Summary of Regulating Transcription and Translation - AQA A Level Biology
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Regulation of transcription and translation – AQA A Level Biology Summary NotesIn eukaryotes, transcription of target genes can be stimulated or inhibited when specific
transcriptional factors move from the cytoplasm to the nucleus
Cells differentiate and specialise by only translating a proportion of genes within their genome. This
control over gene expression is achieved by either:
- inhibiting or stimulating transcription of genes to production of mRNA
- inhibiting or stimulating translation of mRNA to form polypeptides
One way cells control whether genes are transcribed or not is through the action of transcription
factors
For a gene to be transcribed, RNA polymerase must find and bind to the promoter region of a gene
TRANSCRIPTION FACTORS – proteins that bind to the promoter regions of the genes and either
stimulate or inhibit transcription by helping recruit or block RNA polymerase
Transcription factors ordinarily found in cytoplasm. Only move to nucleus and stimulate/inhibit
transcription when activated to do so, typically through action of signalling molecule
The role of the steroid hormone, oestrogen in initiating transcription
1. Oestrogen diffuses from the blood, through the cell surface membrane of target
cells, into the cytoplasm
2. In cytoplasm an oestrogen molecule binds to complementary receptor site on
transcription factor
3. Binding of oestrogen causes a conformational change in transcription factor (change
in tertiary structure), which makes availble the transcription factor’s DNA binding
site
4. Transcription factor can now enter nucleus and bind to promoter region of gene
5. Transcription factor facilitates binding of RNA polymerase to promoter, stimulating
transcription
POINTS TO NOTE:
- Oestrogen is NOT a transcription factor. It is a hormone that can activate
transcription factors
- Oestrogen can diffuse through cell surface membrane by SIMPLE DIFFUSION due to
being LIPID SOLUBLE
- Oestrogen only affects certain target cells, because only specific target cells contain
relevant transcription factor in its cytoplasm
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