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