Transcription factors are proteins that control whether a gene is transcribed. They move from the cytoplasm into the nucleus and bind to specific base sequences in the DNA, usually in or near the promoter of a gene.• Activators help RNA polymerase to bind to the promoter, so transcription starts or increases.
• Repressors bind to the DNA and block RNA polymerase, so transcription is prevented or reduced.Each transcription factor has a DNA-binding site with a shape that fits a particular base sequence, so it only affects genes with that sequence. One transcription factor may control many genes, and one gene may be controlled by several transcription factors. Transcription factors are themselves coded for by genes, so switching on one transcription factor gene can switch on a whole set of other genes.Example: oestrogen
Oestrogen is a lipid-soluble steroid hormone, so it diffuses through the cell surface membrane.
1. In the cytoplasm, oestrogen binds to its receptor, a transcription factor. Before this, the receptor is held in an inactive form.
2. Binding changes the shape of the receptor, so it is released and becomes active.
3. The oestrogen-receptor complex enters the nucleus through a nuclear pore.
4. It binds to the promoter region of target genes and helps RNA polymerase bind, stimulating transcription.Only cells with oestrogen receptors respond, which is why oestrogen affects some tissues, such as the uterus lining, and not others.Transcription factors are needed to switch genes on during development and differentiation, and to let cells respond to changes in their environment.
• Repressors bind to the DNA and block RNA polymerase, so transcription is prevented or reduced.Each transcription factor has a DNA-binding site with a shape that fits a particular base sequence, so it only affects genes with that sequence. One transcription factor may control many genes, and one gene may be controlled by several transcription factors. Transcription factors are themselves coded for by genes, so switching on one transcription factor gene can switch on a whole set of other genes.Example: oestrogen
Oestrogen is a lipid-soluble steroid hormone, so it diffuses through the cell surface membrane.
1. In the cytoplasm, oestrogen binds to its receptor, a transcription factor. Before this, the receptor is held in an inactive form.2. Binding changes the shape of the receptor, so it is released and becomes active.
3. The oestrogen-receptor complex enters the nucleus through a nuclear pore.
4. It binds to the promoter region of target genes and helps RNA polymerase bind, stimulating transcription.Only cells with oestrogen receptors respond, which is why oestrogen affects some tissues, such as the uterus lining, and not others.Transcription factors are needed to switch genes on during development and differentiation, and to let cells respond to changes in their environment.