11. Regulatory Mechanisms

  1. What do cells control to respond appropriately and efficiently to environmental controls?
    • gene expression - which proteins are made
    • enzyme activity - which proteins are on/off
  2. feedback inhibition of a biosynthetic pathway
    • regulation of enzyme activity to determine which pathways are active by responding to product or substrate levels
    • most efficient place is at the first enzymatic step specific to that pathway and no others
  3. allosteric regulation
    • enzyme has two sites:
    • active site - binds the substrate and catalyzes reaction
    • allosteric site - binds the end product, prevents catalysis at the active site
  4. Eukaryotic vs. Bacterial protein synthesis
    • Eukaryotic:
    • transcription - nucleus, translation -cytoplasm
    • introns are removed
    • mature mRNA exported from the nucleus
    • one protein per mRNA

    • Bacterial:
    • transcription - cytoplasm
    • genes are organized in operons, creating polycistronic mRNAs
    • translation occurs in same compartment and same time as transcription
    • multiple genes on one RNA are translated separately
  5. σ factor
    helps RNA polymerase core enzyme recognize and bind to the promoter region
  6. strong vs. weak promoter
    strong promoter - better match with consensus sequence, yields more binding by the σ factor and more transcription of gene

    weak promoter - worse match with consensus sequence, extra transcriptional activators are often needed to turn on transcription of these genes
  7. accessory transcription factors
    • promote or repress transcription of specific genes
    • often contain a DNA-binding domain and a separate regulatory domain that determines when the protein is active
    • often act as dimers and bind to direct or inverted repeats on DNA
  8. repressor
    bind to specific DNA sequences and block transcription of downstream genes
  9. ways to control repressor activity
    • end product of biosynthetic pathways can act as corepressors
    • - arginine is corepressor that binds repressor to prevent RNA poly from transcribing the operon

    • specific enzyme substrates can act as inducers of transcription by blocking action of repressor
    • - lac repressor stops transcription of lac operon unless lactose present, lactose is inducer that binds and inactivates repressor
  10. activators and how they work
    • positive regulators recognize specific DNA sequences in the promoters
    • can increase the affinity of RNA pol for the promoter by providing extra binding contacts for RNA pol
    • - maltose operon activation requires maltose activator protein and maltose
    • can act by bending the DNA to allow better contacts with the promoter
    • can also bind hundreds of bases away and loop the DNA around to touch RNA pol at distant promoter
Card Set
11. Regulatory Mechanisms
general microbiology midterm 1