Bmsc210 Mid2 p2

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Bmsc210 Mid2 p2
2013-03-11 00:01:47
Bmsc210 Mid2 p2

Bmsc210 Mid2 p2
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  1. Two major modes of enzyme regulation
    • – Activity
    • • Temporary inactivation of the protein throughchanges in enzyme structure
    • – Amount
    • • Regulation at the gene level
  2. Gene expression:
    • -transcription of gene into mRNA followed by translation of mRNA into protein (Figure 8.1)
    • - Most proteins are enzymes that carry out biochemical reactions
    • - Constitutive proteins are needed at the same level all the time
    • - Microbial genomes encode many proteins that are not needed all the time
    • - Regulation helps conserve energy and resources
  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. mRNA transcripts generally have a _____half-life (lenght)
    • Short
    • – Prevents the production of unneeded proteins
  5. Regulation of transcription typically requires  proteins that can bind to _____
  6. ______ molecules influence the binding of regulatory proteins to DNA
    • Small
    • – Proteins actually regulate transcription
  7. Most DNA-binding proteins interact with DNA in a _____ manner
  8. DNA-Binding Proteins:
    Specificity is provided by interactions between ___ ____ ____ ____ and chemical groups on the ___ ___ ___ ___ of DNA
    • amino acid side chains
    • bases and sugar–phosphate backbone
  9. ______ of DNA is the main site of protein binding
    Major groove
  10. ___ ___ are frequently  binding sites for regulatory proteins
    Inverted repeats
  11. Homodimeric proteins:
    proteins composed of two identical polypeptides
  12. Protein dimers
    • interact with inverted repeats on DNA
    • – Each of the polypeptides binds to one inverted repeat
  13. Multiple outcomes after DNA binding are possible (2)
    • 1. The binding event can block transcription(negative regulation)
    • 2. The binding event can activate transcription(positive regulation)
  14. Several mechanisms for controlling gene expression in bacteria (3)
    • – environment in which the organism is growing
    • – Presence or absence of specific smallmolecules
    • – Interactions between small molecules and DNA bindingproteins result in control of transcription or translation
  15. Negative control:
    • -a regulatory mechanism that stops transcription
    • -Repressor’s role is inhibitory, so it is called negative control
    • ex: Repression, Induction
  16. Repression:
    • -preventing the synthesis of an enzyme in response to a signal (Figure 8.5)
    • • Enzymes affected by repression make up a small fraction of total proteins
    • • Typically affects anabolic enzymes (e.g., arginine biosynthesis)
    • -used when nutrients are found in environment and arent synthesized
  17. Induction:
    • -production of an enzyme in response to a signal (Figure 8.6)
    • • Typically affects catabolic enzymes (e.g., lac operon)
    • • Enzymes are synthesized only when they are needed
    • – no wasted energy
  18. Inducer:
    • substance that induces enzyme synthesis by removing repressor by binding to it.
    • ex: lactose induces lactase synthase
  19. Corepressor:
    • substance that binds to repressor to represses enzyme synthesis.
    • ex. argine binds to repressor to repress arginine synth
  20. Effectors:
    • -collective term for inducers and repressors
    • -Effectors affect transcription indirectly by binding to specific DNA-binding proteins
  21. Repressor molecules bind to an ___ ___ ___
    allosteric repressor protein
  22. operator
    • -region of DNA near promoter that the Allosteric repressor becomes active and binds to
    • – Operator is located downstream of the promoter
    • – Transcription is physically blocked when repressor binds to operator (Figure 8.7)
  23. Operon:
    -cluster of genes arranged in a linear fashion whose expression is under control of a single operator
  24. Enzyme induction can also be controlled by a ____
    • repressor
    • – Addition of inducer inactivates repressor and transcription can proceed (Figure 8.8)
  25. Positive control:
    • regulator protein activates the binding of RNA polymerase to DNA (Figure 8.9)
    • ex: Maltose catabolism in E. coli
    • – Maltose activator protein cannot bind to DNAunless it first binds maltose
    • 􀅖 Activator proteins bind specifically to certain DNAsequence
    • – Called activator-binding site, not operator
  26. Activator proteins bind specifically to certain ____  sequence
    – Called ___ ___ ___, not operator
    • DNA
    • activator-binding site
  27. Promoters of positively controlled operons  bind ___ly to RNA polymerase
  28. Activator protein helps RNA polymerase recognize ______
    • promoter
    • – May cause a change in DNA structure
    • – May interact directly with RNA polymerase
  29. Activator-binding site may be close to the promoter or ___ ___ base pairs away(Figure 8.11)
    • several hundred
    • -can effect the bonding by bending DNA
  30. How are genes for maltose situated on the chromosome?
    Genes for maltose are spread out over the chromosome in several operons
  31. Each operon has a(n) ___-___ ___
    activator-binding site
  32. regulon
    • -Multiple operons controlled by the same regulatory protein
    • -Regulons exist for positive and negatively controlled systems
  33. Global control systems:
    • regulate expression of many different genes simultaneously
    • different term for regulon
  34. Catabolite repression
    • -an example of globalcontrol
    • – Synthesis of unrelated catabolic enzymes is repressed if glucose is present in growth medium(Figure 8.12)
    • – lac operon is under control of catabolite repression
    • – Ensures the “best” carbon and energy source isused first
  35. Diauxic growth:
    • -two exponential cell growth phases
    • -ex: glucose used up completely before lactose is used
  36. – Cyclic AMP receptor protein (CRP)
    • -an activator protein that controls transcription in catabolite repression
    • -is a form of positive control
  37. Cyclic AMP
    • -a key molecule in many metabolic control systems
    • -highly produced with lack of glucose
    • • It is derived from a nucleic acid precursor
    • • It is a regulatory nucleotide
  38. Effects catabolite repression
    • - Dozens of catabolic operons affected by catabolite repression
    • – Enzymes for degrading lactose, maltose, and other common carbon sources
    • - Flagellar genes are also controlled by catabolite repression
    • – No need to swim in search of nutrients