a) they are more efficient than other RNAs.
b) they have a longer half-life than other RNAs.
c) they are able to degrade other RNAs.
d) they are never degraded.
e) they are anchored in the cell and so stay in one place
9. Antisense RNA can regulate genes by binding to the: （ ）
a) mRNA.
b) Small subunit of the ribosome.
c) RNA polymerase.
d) 23s rRNA.
e) initiator tRNA
10.下面哪些真正是乳糖操纵子的诱导物?( )
a)乳糖
b)蜜二糖
c)O—硝基苯酚—β—半乳糖苷(ONPG)
d)异丙基—β—半乳糖苷
e)异乳糖
11.下面哪一项是对三元转录复合物的正确描述：( )
a)σ因子、核心酶和双链 DNA在启动子形成的复合物
b)全酶、 TFⅠ和解链 DNA双链形成的复合物
c)全酶、模板 DNA和新生RNA形成的复合物
d)三个全酶在转录起始位点(tsp)形成的复合物
e)σ因子、核心酶和促旋酶形成的复合物
12. σ因子和 DNA之间相互作用的最佳描述是：( )
a)游离和与 DNA结合的σ因子的数量是一样的，而且σ因子合成得越多，转录起 始的机会越大
b)σ因子通常与 DNA结合，且沿着 DNA搜寻，直到在启动子碰到核心酶。它与DNA的结合不需依靠核心酶
c)σ因子通常与 DNA结合，且沿着RNA搜寻，直到碰到启动子，在有核心酶存在的时候与之结合
d)σ因子是 DNA依赖的RNA聚合酶的固有组分，它识别启动子共有序列且与全酶结合
e)σ因子加入三元复合物而启动RNA合成
三、填空题：
1. A catabolic pathway is often regulated by the amount of whereas an anabolic pathway is usually regulated by the amount of . The lac operon is an example of genes that encode a pathway.
2．原核生物中Attenuator存在于 序列中，其调控机理是 Enhancer存在于 序列中，其调控机理是 。
3．能够诱导操纵子但不是代谢底物的化合物称为 诱导物。能够诱导乳糖操 纵子的化合物 就是其中一例。这种化合物同 蛋白质结合，并使之与 分离。乳糖操纵子的体内功能性诱导物是 。
4.色氨酸是一种调节分子，被视为 。它与一种蛋白质结合形成 。 乳糖操纵子和色氨酸操纵于是两个 控制的例子。 cAMP—CAP蛋白通过 控制起作用。色氨酸操纵子受另一种系统一的调控，它涉及到第一个结构基因被转录前的转录 。
四、问答题：
1. What are operon? What is a structural gene?
2. What would likely be the consequence of a mutation that drastically changed the
sequence of the operator for the Lac operon?
3. Describe the inducible and repressible modes of gene regulation in bacteria. Include a diagram showing the following: operon, inducer, repressor, corepressor, promoter..
4. DRAW the process of repression. On your graphic, label the following items: promoter, operator, repressor protein, and RNA polymerase (RNAP).
5. Draw diagrams of the lac operon that illustrate (a) negative control and (b) positive control.
6. Indicate how Z and Y expressions are regulated in the following genotypes in partially diploid cell: I+O+Z—Y+/I+OCZ+Y— ； ICO+Z—Y+/ I+OCZ+Y— ； ISO+Z+Y—/ I+OCZ—Y+.
7. How do mutations in the Lux R gene affect the expression of the Lux operon.
8. Use a diagram to illustrate how arabinose operon is regulated in the a) absence of arabinose, b) presence of arabinose , c) b and glucose . d) b and cAMP.
