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【判断题】
操作员权限一旦被使用,仍可以修改或删除A.
正确
B.
错误
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举一反三
【单选题】Enzymes that remove nucleotides one at a time from the end of a DNA molecule are called
A.
Ligases
B.
Exonucleases
C.
Endonucleases
D.
Modifying enzymes
【判断题】Like the chromatin-remodeling complexes, the enzymes that modify histone tails are tightly regulated. They are brought to particular chromatin regions mainly by interactions with proteins that bind to...
A.
正确
B.
错误
【单选题】Various chemicals can induce mutations by modifying the nucleotides, causing base deletions or mimicking bases and substituting for them in the DNA chain. An example of the latter is:
A.
acridine
B.
5-bromouracil
C.
mitomycin
D.
nitrous oxide
【单选题】以下哪种处理不能引起细菌的DNA突变？
A.
Base analogs 碱基类似物
B.
DNA modifying agents DNA修饰剂
C.
Intercalating agents 插入剂
D.
氨基酸
【多选题】How do transcription regulators, general transcription factors, and RNA polymerase gain access to the underlying DNA in highly packed chromosomes?
A.
In eukaryotic cells, activator and repressor proteins can exploit the mechanisms used to package DNA to help turn genes on and of.
B.
Chromatin structure can be altered by chromatin-remodeling complexes and by enzymes that covalently modify the histone proteins that form the core of the nucleosome. Many gene activators take advantage of these mechanisms by attracting such chromatin-modifying proteins to promoters.
C.
For example, the recruitment of histone acetyltransferases promotes the attachment of acetyl groups to selected lysines in the tail of histone proteins; these acetyl groups themselves attract proteins that promote transcription, including some of the general transcription factors. And the recruitment of chromatin-remodeling complexes makes nearby DNA more accessible. These actions enhance the efficiency of transcription initiation.
D.
In a similar way, gene repressor proteins can modify chromatin in ways that reduce the efficiency of transcription initiation. For example, many repressors attract histone deacetylases—enzymes that remove the acetyl groups from histone tails, thereby reversing the positive effects that acetylation has on transcription initiation.
【简答题】DNA Modifying Enzymes
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