prokaryotic gene regulation - prokaryotes react according to environmental changes
- regulatory molecules can increase/decrease initiation rate
- induction >> prevent negative regulator from binding >> produces proteins
- repression >> makes negative regulator bind >> stops protein production
- operons - multiple genes part of a single gene expression unit
- all part of same mRNA >> controlled by same promoter
- genes for same biochemical pathway organized this way
- repressors - proteins that bind to regulatory sites on DNA >> prevent start of transcription
- trp operon - repressed in presence of tryptophan, induced in absence of tryptophan
- tryptophan repressor can’t bind to DNA unless it binds to 2 tryptophan molecules first
- lac operon - makes enzymes when lactose available
- lack of lactose >> lack of allolactose (metabolite of lactose) >> repressor allowed to bind to DNA >> stops production of enzymes for lactose
- activators - binds DNA to stimulate transcription initiation
- catabolite activator protein (CAP) - activator protein stimulating transcription for operons coding for sugar catabolism
- binding controlled by cAMP (inversely related to glucose level)
- little glucose >> lots of cAMP >> CAP able to bind to DNA >> stops catabolic operons
- switches combined when 1 used for more than 1 reaction
eukaryotic gene regulation - much more complex than in prokaryotes
- DNA arranged in chromatin >> makes protein-DNA interactions difficult
- transcription/translation occurs in 2 places
- basal transcription factors - used for making transcription apparatus, getting RNA pol II to promoter
- TFIID - contains TATA-binding protein for promoter
- transcription-associated factors (TAF) - additional accessory factors
- initiation complex - contains all factors and polymerase, needs other specific factors to work faster than basal level
- specific transcription factors - increases rate of transcription
- aka activators
- has domain that interacts w/ transcription apparatus
- enhancers - binding sites for specific transcription factors
- can act over large distances by bending DNA strand
- coactivator/mediator - binds transcription factor to another part of transcription apparatus
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