28(1).rtf - Name Date A B C D E A B C D E 1.“Housekeeping...

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Name: __________________________ Date: _____________ 1.“Housekeeping genes” in bacteria are commonly expressed constitutively, but not all of these genes are expressed at the same level (the same number of molecules per cell). The primary mechanism responsible for variations in the level of constitutive enzymes from different genes is that: A) all constitutive enzymes are synthesized at the same rate, but are not degraded equally. B) their promoters have different affinities for RNA polymerase holoenzyme. C) some constitutively expressed genes are more inducible than others. D) some constitutively expressed genes are more repressible than others. E) the same number of mRNA copies are made from each gene but are translated at different rates. 2.Which of the following statements correctly describes promoters in E. coli ? 3.The operator region normally can be bound by: 4.Small signal molecules that regulate transcription are not known to: 5.The diagram below represents a hypothetical operon in the bacterium E. coli. The operon consists of two structural genes (A and B), which code for the enzymes A-ase and B-ase, Page 1
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respectively, and also includes P (promoter) and O (operator) regions as shown. When a certain compound (X) is added to the growth medium of E. coli, the separate enzymes A-ase and B-ase are both synthesized at a 50-fold higher rate than in the absence of X. (X has a molecular weight of about 200.) Which of the following statements is true of the operon described above? A) All four genes (A, B, O, and P) will be transcribed into an mRNA that will then be translated into four different proteins. B) The 3 ' end of the mRNA from the operon will correspond to the left end of the operon as drawn. C) The 5 ' end of the messenger from this operon will correspond to the right end of the operon as drawn. D) The repressor for this operon binds just to the right of A. E) When RNA polymerase makes mRNA from this operon, it begins RNA synthesis just to the left of gene A.
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