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【单选题】
下列有关人体必需化学元素的说法错误的是（ ）A.
氟摄入过多可能导致氟
B.
成人碘含量过引起甲状腺疾病
C.
儿童缺锌会影响骨骼、牙齿的生长
D.
过量服用补铁剂可造成胃肠道出血
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【简答题】PLC的主要工作过程的中心内容包括:
【多选题】How do retroviruses proliferate in host cells?
A.
Like retrotransposons, retroviruses use the enzyme reverse transcriptase to convert RNA into DN The enzyme is encoded by the retroviral genome, and a few molecules of the enzyme are packaged along with the RNA genome in each virus particle. When the single-stranded RNA genome of the retrovirus enters a cell, the reverse transcriptase brought in with it makes a complementary DNA strand to form a DNA/RNA hybrid double helix.
B.
The RNA strand is removed, and the reverse transcriptase (which can use either DNA or RNA as a template) now synthesizes a complementary DNA strand to produce a DNA double helix. This DNA is then inserted, or integrated, into a randomly selected site in the host genome by a virally encoded integrase enzyme. In this integrated state, the virus is latent: each time the host cell divides, it passes on a copy of the integrated viral genome, which is known as a provirus, to its progeny cells.
C.
The next step in the replication of a retrovirus—which can take place long after its integration into the host genome—is the copying of the integrated viral DNA into RNA by a host-cell RNA polymerase, which produces large numbers of single-stranded RNAs identical to the original infecting genome.
D.
These viral RNAs are then translated by the host-cell ribosomes to produce the viral shell proteins, the envelope proteins, and reverse transcriptase—all of which are assembled with the RNA genome into new virus particles.
【简答题】American researchers have developed a technique that may become an important tool in fighting virus from attacking its target-cells in the body's defense system．When virus enters the blood，i...
【简答题】Ⅰ.(1)某化学兴趣小组欲从下列装置中选取必要的装置制取（NH 4 ） 2 SO 4 溶液，连接的顺序（用接口序号字母表示）是：a 。 (2)将装置C中两种液体分离开的操作名称是__ _ __。装置D的作用是 。 Ⅱ.过氧化钙可以用于改善地表水质、处理含重金属粒子废水和治理赤潮，也可用于应急供氧等。工业上生产过氧化钙的主要流程如下： 已知 2 ·8H 2 O呈白色，微溶于水。I 2 +2S ...
【单选题】What occurs when a temperate phage enters a state called lysogeny? ( )
A.
Most viral genes are expressed
B.
The bacterial cell is lysed
C.
Many new viruses are produced
D.
Most normal bacterial functions are turned off.
E.
The virus may become integrated into the host genome.
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