Control of Transcription I and II: Control of Enzyme Activity and Trp Operon

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Control of Transcription I and II: Control of Enzyme Activity and Trp Operon
2012-12-01 00:41:00
Bio Final

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  1. a.      Cells precisely and intricately regulate their __ in response to environmental conditions
                                                                  i.      Multicellular eukaryotes have multiple cell types with same __but different subset of genes
    • gene expression
    • genome
  2. a.      Bacteria Responses and Regulation
                                                                  i.      __favored bacteria that express only the genes whose products are needed by cell
                                                                ii.      If bacteria lives in environment lacking an amino acid (for example, tryptophan), the cell responds by... what does it do?; if later exposed to tryptophan through tryptophan-rich meal being ingested, it will __
    • Natural selection
    • activating a metabolic pathway that makes tryptophan from another compound
    • stop producing it, saving its resources
  3. Metabolic control on two levels
    • 1.      First, cells adjust activity of enzymes already present
    • 2.      Second, cells adjust the production level of certain enzymes; they can regulate the expression of genes encoding the enzymes
  4. 1.      activity of enzymes already present
    a.      (fast or slow); relies on __of many enzymes to chemical cues that increase or decrease their __
                                                                                                                                          i.      First enzyme in tryptophan synthesis pathway is inhibited by pathway’s end product
    1.      If tryptophan accumulates in cell, it shuts down synthesis of more tryptophan by __2.__, typical of __pathways, allows a cell to adapt to short-term fluctuations
    • Fast
    • sensitivity
    • catalytic activity
    • inhibiting enzyme activity
    • Feedback inhibition
    • anabolic
  5. adjust the production level of certain enzymes

    a.      If environment provides all needed tryptophan, the cell stops making the enzymes that __
                                                                                                                                          i.      The control of enzyme production occurs at __
    1.      Many genes of the bacterial genome are switched on or off by changes in the metabolic status of the cell
    a.      One basic mechanism for this control of gene expression in bacteria is __
    • catalyze the synthesis of tryptophan
    • transcription level
    • operon model
  6. a.      E. coli synthesizes tryptophan from precursor molecule in __
                                                                  i.      Each reaction in multistep pathway is catalyzed by a specific enzyme and the __ that code for the subunits of these enzymes are clustered together on bacterial chromosome
                                                                ii.      A single __serves all five genes, which constitute a __
    • multistep pathway
    • five genes
    • promoter
    • transcription unit
  7. 1.      Transcription gives rise to one long mRNA molecule that codes for the __ making up enzymes of tryptophan pathway
    a.      The cell can translate this one mRNA into five separate polypeptides because what?
    • five polypeptides
    • RNA is punctuated with start and stop codons that signal where coding sequence for each polypeptide begins and ends
  8.                                                               i.      Advantage of grouping genes of related function into one transcription unit is that a single “on-off switch” can control whole cluster of functionally related genes= __
    coordinately controlled
  9. 1.      When E. coli cell must make tryptophan for self due to lack of amino acid, all enzymes for metabolic pathway are synthesized at one time
    a.      The switch is a segment of DNA called the __
                                                                                                                                          i.      Both location and name suit function
    1.      Positioned within __or between __2.      Controls access of __to genes
    • operator
    • promoter
    • promoter and enzyme-coding genes
    • RNA polymerase
  10. a.      Altogether, the __—the entire stretch of DNA required for enzyme production for the tryptophan pathway—constitute __
    • operator, promoter, and genes they control
    • operon
  11.                                                               i.      By itself the trp operon is __; RNA polymerase can or cannot do what?

    1.      Can be __ by protein called the trp __
    a.      The repressor binds to operator and blocks RNA polymerase attachment to promoter, preventing transcription of genes
    b.      Repressor proteins specific for operator of particular operon
    • turned on
    • can bind to promoter and transcribe genes of operon
    • switched off
    • repressor
  12. 1.      Trp repressor is protein product of __ called trpR, which is located some distance from the trp __and has own __
    2.      Regulatory genes expressed continuously, although at a low rate, and a few trp repressor molecules are always present
    • regulatory gene
    • operon
    • promoter
  13. 1.      Reason it is not turned off permanently:
    • 1.       
    • a.      Binding of repressors to operators is reversible
    • b.      Second, the trp repressor is an Allosteric protein, with two alternative shapes, active and inactive
  14.                                                                                                                                       i.      __vacillates between two states:
    1.      __
    a.      Duration of each state depends on the __
    • Operator
    • One with repressor bound and one without
    • number of active repressor molecules around
  15.                                                                                                                                       i.      Trp repressor synthesized in an __form with little affinity for the trp operator
    1.      Only if tryptophan binds to trp repressor at an Allosteric site does the repressor protein change to the active form that can attach to the operator, doing what?
    • inactive
    • turning the operon off
  16. 1.      Tryptophan functions as a __, a small molecule that cooperates with a repressor protein to switch an operon off
    a.      As it builds up, more molecules do what?
                                                                                                                                          i.      If levels drops, __ of the operon’s genes resumes
    • corepressor
    • ssociate with repressor, which bind to operator and shut down production of tryptophan pathway enzymes
    • transcription