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【判断题】
在开清棉联合机的排列组合中,一般先安排握持打击的开棉机,再安排自由打击的开棉机。A.
正确
B.
错误
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【单选题】21世纪,科技问题将越来越突出。核心问题是科学技术进步应服务于全人类、服务于世界和平、发展与进步的崇高事业,而不能危害人类自身。这就要求广大科技工作者( )
A.
要从实际出发,实事求是
B.
要注意培养科学思维方法
C.
要树立和坚持符合人类根本利益的价值观
D.
要坚持理论与实践的有机统一
【单选题】乙消费 100 单位的 X 和 50 单位的 Y ,若 P x 从 2 元上升到 3 元, P y 仍然不变,为使消费情况不变,他的收入需增加多少?
A.
100
B.
120
C.
150
D.
200
【单选题】关于期门穴位的定位正确的是( )
A.
在侧腹部,当第11肋游离端的下方
B.
在胸部,乳头直下,第6肋间隙,前正中线旁开4寸
C.
在侧腰部,章门后1.8寸,当第12肋骨游离端的下方
D.
在上腹部,当乳头直下,第7肋间隙,前正中线旁开4寸
E.
在侧腹部,章门下1.8寸,当第11肋骨游离端下方垂线与脐水平线的交点上
【单选题】21世纪,科技问题将越来越突出。核心问题是科学技术进步应服务于全人类、服务于世界和平、发展与进步的崇高事业,而不能危害人类自身。这就要求广大科技工作者( ) A、要从实际出发,实事求是
A.
要注意培养科学思维方法
B.
要树立和坚持符合人类根本利益的价值观
C.
要坚持理论与实践的有机统一
【多选题】How are tRNAs processed in bacteria and eukaryotes?
A.
Most cells have 40 to 50 distinct tRNAs, and eukaryotic cells have multiple copies of many of the tRNA genes. Transfer RNAs are derived from longer RNA precursors by enzymatic removal of nucleotides from the 5′ and 3′ ends. In eukaryotes, introns are present in a few tRNA transcripts and must be excised. Where two or more different tRNAs are contained in a single primary transcript, they are separated by enzymatic cleavage.
B.
The endonuclease RNase P, found in all organisms, removes RNA at the 5′ end of tRNAs. This enzyme contains both protein and RN The RNA component is essential for activity, and in bacterial cells it can carry out its processing function with precision even without the protein component. RNase P is another example of a catalytic RNA, as described in more detail below. The 3′ end of tRNAs is processed by one or more nucleases, including the exonuclease RNase D.
C.
Transfer RNA precursors may undergo further posttranscriptional processing. The 3′-terminal trinucleotide CCA(3′) to which an amino acid is attached during protein synthesis is absent from some bacterial and all eukaryotic tRNA precursors and is added during processing. This addition is carried out by tRNA nucleotidyltransferase, an unusual enzyme that binds the three ribonucleoside triphosphate precursors in separate active sites and catalyzes formation of the phosphodiester bonds to produce the CCA(3′) sequence. The creation of this defined sequence of nucleotides is therefore not dependent on a DNA or RNA template—the template is the binding site of the enzyme.
D.
The final type of tRNA processing is the modification of some bases by methylation, deamination, or reduction. In the case of pseudouridine, the base (uracil) is removed and reattached to the sugar through C-5. Some of these modified bases occur at characteristic positions in all tRNAs.
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