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【多选题】
Why do we think that the ribosome is a ribozyme?A.
The rRNAs are folded into highly compact, precise three-dimensional structures that form the core of the ribosome. In contrast to the central positioning of the rRNAs, the ribosomal proteins are generally located on the surface, where they fill the gaps and crevices of the folded RN
B.
The main role of the ribosomal proteins seems to be to help fold and stabilize the RNA core, while permitting the changes in rRNA conformation that are necessary for this RNA to catalyze efficient protein synthesis.
C.
Not only are the three tRNA-binding sites (the A, P, and E sites) on the ribosome formed primarily by the rRNAs, but the catalytic site for peptide bond formation is formed by the 23S rRNA of the large subunit; the nearest ribosomal protein is located too far away to make contact with the incoming amino acid or with the growing polypeptide chain.
D.
The catalytic site in this RNA—a peptidyl transferase—is similar in many respects to that found in some protein enzymes: it is a highly structured pocket that precisely orients the two reactants—the elongating polypeptide and the amino acid carried by the incoming tRNA—thereby greatly increasing the likelihood of a productive reaction.
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【简答题】Foreign trade
【单选题】Why do many countries attach increasing importance to foreign trade?
A.
Because their economies depend highly on foreign trade.
B.
Because they want to keep foreign trade growing faster.
C.
Because foreign trade can increase the productivity of the industries.
D.
Because foreign trade creates jobs that have both political and economic significance.
【简答题】foreign trade
【简答题】判别直线与平面是否平行。( CD∥EF),将“平行”,“不平行”结果写在题后对应的标号处: (1) (2)
【简答题】下列各种说法中错误的是______（填序号） ①过一点有且只有一条直线与已知直线平行 ②在同一平面内，两条不相交的线段是平行线段 ③两条直线没有交点，则这两条直线平行 ④在同一平面内，若直线AB ∥ CD，直线AB与EF相交，则CD与EF相交．
【单选题】Foreign trade
A.
allows a country to have a greater variety of products at a lower cost than if it tried to produce everything at home.
B.
allows a country to avoid trade-offs.
C.
makes the members of a country more equal.
D.
increases the scarcity of resources.
E.
is none of the above.
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