Some genes are transcribed all the time to produce constituitive proteins; others are only 'switched on' when their protein products are required.Transcription factors bind to the promoter region of a gene. This may increase or decrease the transcription of the gene. Their roles are to make sure that genes are expressed in the correct cell at the correct time and to the correct extent.
Effects of transcription factors:
- form part of the protein complex that binds to the promoter region of the gene
- activate appropriate genes in sequence
- determination of sex in animals
- allow responses to environmental stimuli
- regulate cell cycle, growth and apoptosis
- give hormones their effect
Gibberellin (a plant hormone) controls seed germination in plants such as wheat and barley by stimulating the synthesis of amylase.
- DELLA protein inhibits the binding of a transcription factor to the gene promoter PIF
- gibberellin causes the breakdown of DELLA protein
- gibberellin allows PIF to bind to its target promoter
- transcription of the gene can take place
- increases amylase production
16.3 Gene control
Some genes are transcribed all the time to produce constitutive proteins; others are only ‘switched on’ when their protein products are required. a) distinguish between structural and regulatory genes and between repressible and inducible enzymes b) explain genetic control of protein production in a prokaryote using the lac operon c) explain the function of transcription factors in gene expression in eukaryotes
d) explain how gibberellin activates genes by causing the breakdown of DELLA protein repressors, which normally inhibit factors that promote transcription
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