Microbiology 3-5

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Microbiology 3-5
2013-11-12 20:34:02

Study guide 3-5
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  1. Regulation by riboswitches.Explain the mechanism by which riboswitches 
control translation
    • Bind to the 5’ elements of mRNA. Alters the folding of mRNA leader
    • and inhibits ribosome binding and initiation of translation.

    Antisense RNA from micF stops translation of ompF RNA
  2. Explain what an sRNA or antisense RNA is
    RNA that is not t,r,or mRNA. They regulate translation by base pairing to the leader region of the mRNA.
  3. Describe how antisense RNAs regulate translation:
    They are complementary to mRNA, they can inhibit or promote translation. Working with Hfq
  4. Explain what a global regulatory system is:
    regulatory systems that affect many genes and pathways simultaneously. These are mechanisms that can affect multiple operons.
  5. Describe Regulon gene regulation:
    a collection of genes that is controlled by a common regulatory protein.

    You have 1 regulatory protein that is involved in regulating transcription of multiple genes.
  6. Describe Modulon gene regulation:
    an operon network under control of a common global protein but each operon is controlled by its own regulators.

    • You have a regulatory protein that regulates the operons, but in addition each operon has its own regulatory protein, so two per operon. These guys can combine and work
    • separately
  7. Describe Stimulon gene regulation:
    • all operons respond together in a coordinated way, may contains
    • modulons and regulons.

    • Stimulus affects the regulons and modulons in the cell, it can
    • affect multiples of these.
  8. Discuss the use of alternate sigma factors in global regulation:
    Can immediately change expression of genes.

    How transcription normally works: a sigma factor is involved in binding to the promoter of each gene, whether this binds depends on the positive and negative control. Sometimes the cell produces other sigma factors! The cell produces sigma 70 when it is in the lag phase, when it is produced it can now do the same thing as the main sigma factor but it will be preferential towards specific genes, these genes would be important in the exponential cycle. Sigma S is produced when the cell is in stress (stationary phase). Sigma C gets made in hot conditions.
  9. Explain what is meant by diauxic growth:
    The growth of a bacteria when it starts using glucose, lags and then starts using lactose
  10. How does Diauxic growth work?
    • CAP protein (positive-activator,
    • negative-repressor) exists in two forms:

    Active when cAMP is bound

    • Inactive when cAMP is low or
    • not present.

    cAMP levels are controlled by adenyl cyclase

    Low or no glucose= adenyl cyclase is active

    • No glucose: CAP is active,
    • promotes transcription of operons.
  11. Describe the mechanism of catabolite repression using the lac operon in E.coli:

    • Positive control- High Glucose-low cAMP, CAP is not activated (adenyl cyclase is not
    • working)

    • Low glucose- High cAMP, CAP is activated and binds to the CAP site. (adenyl cyclase
    • is working) Transcription of genes is promoted (lac Z,Y,A)
  12. Lactose but no glucose
  13. Lactose and Glucose
  14. Neither lactose or glucose
  15. Glucose but no lactose