Card Set Information

2010-09-24 21:11:02

9 Micro
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  1. Gene expression
    transcription of gene into mRNA followed by translation of mRNA into a protein
  2. Constitutive
    proteins are needed at the same level all the time
  3. Two major levels of regulation in the cell
    • One controls the activity of preexisting enzymes
    • Posttranslational regulation
    • Very rapid process (seconds)

    • One controls the amount of an enzyme
    • Regulate level of transcription
    • Regulate translation
    • Slower process (minutes)
  4. Proteins actually regulate transcription
  5. Helix-turn-helix
    DNA Binding Protein

    • First helix is the recognition helix
    • Second helix is the stabilizing helix
    • Many different DNA-binding proteins from Bacteria contain helix-turn-helix
    • lac and trp repressors of E. coli
  6. Zinc finger
    DNA Binding Protein

    • Protein structure that binds a zinc ion
    • Typically two or three zinc fingers on proteins that use them for DNA binding
  7. Leucine Zipper
    • Leucine residues are spaced every seven amino acids
    • Does not interact directly with DNA unlike helix-turn-helix or Zinc Finger

  8. Multiple outcomes after DNA binding are possible
    1)DNA-binding protein may catalyze a specific reaction on the DNA molecule (i.e., transcription by RNA polymerase)

    2)The binding event can block transcription (negative regulation)

    3)The binding event can activate transcription (positive regulation)
  9. Negative control
    a regulatory mechanism that stops transcription

    Repression and Induction
  10. Repression
    preventing the synthesis of an enzyme in response to a signal

    Enzymes affected by any repression make up a small fraction of total proteins in the cell

    Typically affects anabolic enzymes (i.e., arginine biosynthesis)
  11. Induction
    production of an enzyme in response to a signal

    • Typically affects catabolic enzymes (i.e., lac operon)
    • Enzymes are synthesized only when they are needed so no wasted energy
  12. Effectors
    collective term for inducers and Corepressors (which induce or repress enzyme synthesis)

    Effectors affect transcription indirectly by binding to specific DNA-binding proteins

    • Repressor molecules bind to an allosteric repressor protein
    • Allosteric repressor becomes active and binds to region of DNA near promoter called the operator
  13. Operon
    cluster of genes arranged in a linear fashion whose expression is under control of a single operator

    • Operator is located downstream of the promoter
    • Transcription is physically blocked when repressor binds to operator
  14. kinase
    an enzyme that phophorylates compounds