overview of transcriptional control - important for adaptation, development, homeostasis 

• regulating promoter access - controls start of transcription
  • binding proteins to regulatory sequence blocks/catalyzes binding of RNA polymerase
  • promoter (nucleotide sequence) tells polymerase where to start transcribing
• transcriptional control in prokaryotes - prokaryotes grow/divide as quickly as possible
  • adjusts cell’s activities to immediate environment
  • reversible changes, lets cell adjust enzymes levels up/down
• transcriptional control in eukaryotes - eukaryotes protected from changes in immediate environment
  • regulates body as a whole, not just individual cells
  • controls growth/development
  • enzymes for a particular developmental change stops working after the change takes place
• posttranscriptional control - changes mRNA produced by transcription

DNA-binding motifs - proteins have special structure to bind to DNA on major groove 

• major groove - contains hydrogen atoms, hydrogen bond donors/acceptors, hydrophobic methyl groups
• helix-turn-helix - most common motif
  • made up of 2 alpha-helical segments connected by nonhelical segment
  • recognition helix - fits into major groove of DNA molecule
  • more protein-DNA-binding sites increases strength of bond between them
• homeodomain motif - helix-turn-helix motfi in center
• zinc finger motif - uses zinc to coordinate binding to DNA
  • more zinc fingers in cluster >> stronger link between protein/DNA
• leucine zipper motif - 2 different protein subunits make a single binding site
  • Y-shape, allows for greater flexibility in gene control