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chapter28 - Chapter 28 Regulation of Gene Expression...

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Chapter 28 Regulation of Gene Expression Chapter 28 Regulation of Gene Expression Multiple Choice Questions 1. Principles of gene regulation Page: 1116 Difficulty: 2 Ans: B “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. Principles of gene regulation Pages: 1116-1117 Difficulty: 2 Ans: D Which of the following statements correctly describes promoters in E. coli ? A) A promoter may be present on either side of a gene or in the middle of it. B) All promoters have the same sequence that is recognized by RNA polymerase holoenzyme. C) Every promoter has a different sequence, with little or no resemblance to other promoters. D) Many promoters are similar and resemble a consensus sequence, which has the highest affinity for RNA polymerase holoenzyme. E) Promoters are not essential for gene transcription, but can increase its rate by two- to three-fold. 3. Principles of gene regulation Pages: 1117-1118 Difficulty: 2 The operator region normally can be bound by: 4. Principles of gene regulation Pages: 1117-1118 Difficulty: 2 Small signal molecules that regulate transcription are not known to: 70
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5. Principles of gene regulation Pages: 1117-1119 Difficulty: 2 Ans: E 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, 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
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