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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.
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【判断题】车钩提杆是为了开启车钩 而 设置的。 ( )(1 . 0分)
A.
正确
B.
错误
【判断题】定位基准可分为粗基准、半精基准和精基准三种。( )
A.
正确
B.
错误
【简答题】根据工件上定位基准的表面状态不同,定位基准分为精基准和( )。
【单选题】子痫前期病人在用硫酸镁治疗中出现膝反射消失,呼吸12次/分,尿量30ml/小时,应采取下列哪种抢救措施:
A.
10%葡萄糖酸钙10ml缓慢静脉推注
B.
10%钙剂快速静脉点滴
C.
立即停用硫酸镁
D.
停用硫酸镁,10%葡萄糖酸钙10ml静推3分钟以上
E.
以上方法都是错误的
【简答题】请用以下助词填空 을/를 은/는 에 에서 식당 갑니다.
【单选题】采用特定的培养基,使待分离的微生物生长更快,从而使它们的相对数量增加,有利于进一步的分离。这种培养基称为_______。
A.
选择培养基
B.
富集培养基
C.
基础培养基
D.
合成培养基
【判断题】定位基准分为粗基准和精基准。()
A.
正确
B.
错误
【简答题】定位基准分为 基准和精基准。
【简答题】定位基准分为 和精基准。
【单选题】车钩( )是为了开启车钩而设置的,客车主要采用下作用式。
A.
摆块
B.
钩舌
C.
钩舌销
D.
提杆
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