)RNA Polymerases Carry Out Tranion
RNA聚合酶参与了转录反应
The enzymes that perform tranion are called RNA polymerases.
执行转录反应的酶称为RNA聚合酶。
Like the DNA polymerase that catalyzes DNA replication (discussed in Chapter 5), RNA polymerases catalyze the formation of the phosphodiester bonds that link the nucleotides together to form a linear chain.
像DNA聚合酶类似，催化DNA复制(在第5章讨论)：RNA聚合酶催化的形成核苷酸的磷酸二酯键,链接在一起,形成一个线性链。
The RNA polymerase moves stepwise along the DNA, unwinding the DNA helix just ahead of the active site for polymerization to expose a new region of the template strand for complementary base-pairing.
沿着DNA,RNA聚合酶举措逐步解除DNA螺旋在聚合的活性部位暴露一个新区域模板链的互补碱基对。
In this way, the growing RNA chain is extended by one nucleotide at a time in the 5?-to-3? direction (Figure 6–9).
通过这种方式,越来越多的RNA链延长一个核苷酸的5?3?方向(图6 - 9)。
The substrates are ribonucleoside triphosphates (ATP, CTP, UTP, and GTP); as in DNA replication, the hydrolysis of high-energy bonds provides the energy needed to drive the reaction forward (see Figure 5–4 and Movie 6.2).
基质是核糖核苷三磷酸腺苷(ATP,CTP,UTP,和三磷酸鸟苷); 在DNA复制,高能债券的水解提供所需要的能量向前驱动反应(见图5 - 4和6.2视频)。
The almost immediate release of the RNA strand from the DNA as it is synthesized means that many RNA copies can be made from the same gene in a relatively short time, with the synthesis of additional RNA molecules being started before the previous RNA molecules are completed (Figure 6–10).
几乎立即释放的RNA链的DNA合成意味着许多可以进行RNA复制同样的基因在一个相对短的时间内,与额外的RNA分子的合成开始之前完成前面的RNA分子(图6 - 10)。
When RNA polymerase molecules follow hard on each other’s heels in this way, each moving at about 50 nucleotides per second, over a thousand trans can be synthesized in an hour from a single gene.
当RNA聚合酶分子遵循紧对方的通过这种方式,每个移动以每秒大约50个核苷酸,超过一千的记录中可以合成一个小时从单个基因。
Although RNA polymerase catalyzes essentially the same chemical reaction as DNA polymerase, there are some important differences between the activities of the two enzymes.
尽管RNA聚合酶DNA聚合酶催化相同的化学反应,有一些重要的区别两种酶的活动。首先,最明显的是,RNA聚合酶催化核苷酸的连接,而不是脱氧核苷酸。
First, and most obviously, RNA polymerase catalyzes the linkage of ribonucleotides, not deoxyribonucleotides.
首先,最明显的是,RNA聚合酶催化核苷酸的连接,而不是脱氧核苷酸。
Second, unlike the DNA polymerases involved in DNA replication, RNA polymerases can start an RNA chain without a primer.
第二,与DNA聚合酶参与DNA复制,RNA聚合酶可以开始一个RNA链引物。
This difference is thought possible because tranion need not be as accurate as DNA replication (see Table 5–1, p. 244).
这种差异被认为可能是因为转录DNA复制不需要尽可能准确的(见表5 - 1,p . 244)。
RNA polymerases make about one mistake for every 104 nucleotides copied into RNA (compared with an error rate for direct copying by DNA polymerase of about one in 107 nucleotides); and the consequences of an error in RNA tranion are much less significant as RNA does not permanently store genetic information in cells.
RNA聚合酶对一个错误每104个核苷酸复制到RNA(相比之下,直接复制DNA聚合酶的错误率约在107核苷酸);和一个错误的后果在RNA转录为RNA的意义并不永久存储在细胞遗传信息。
Finally, unlike DNA polymerases, which make their products in segments that are later stitched together, RNA polymerases are absolutely processive; that is, the same RNA polymerase that begins an RNA molecule must finish it without dissociating from the DNA template.
最后,与DNA聚合酶,使其产品在细分后缝合,RNA聚合酶绝对是前进的,也就是说,同样的RNA聚合酶RNA分子必须完成它没有开始逃避DNA模板的。
Although not nearly as accurate as the DNA polymerases that replicate DNA, RNA polymerases nonetheless have a modest proofreading mechanism.
虽然不是那么准确复制的DNA聚合酶DNA,RNA聚合酶仍然有一个适度的校对机制。
If an incorrect ribonucleotide is added to the growing RNA chain, the polymerase can back up, and the active site of the enzyme can perform an excision reaction that resembles the reverse of the polymerization reaction, except that a water molecule replaces the pyrophosphate and a nucleoside monophosphate is released.
如果一个错误的核苷酸被添加到RNA链增长,聚合酶可以备份,和酶的活性部位可以进行切除反应,类似于反向的聚合反应,除了水分子取代了焦磷酸核苷一磷酸是释放。
Given that DNA and RNA polymerases both carry out template-dependent nucleotide polymerization, it might be expected that the two types of enzymes would be structurally related.
鉴于DNA和RNA聚合酶进行template-dependent核苷酸聚合,它可能会两种类型的酶将结构相关。
However, x-ray crystallographic studies reveal that, other than containing a critical Mg2+ ion at the catalytic site, the two enzymes are quite different.
然而： X射线晶体研究表明,除了包含一个关键Mg2 +离子催化部位,这两个酶有很大的不同。
Template-dependent nucleotide-polymerizing enzymes seem to have arisen at least twice during the early evolution of cells.
模板依赖的核酸酶似乎至少两次出现在早期进化的细胞。
One lineage led to the modern DNA polymerases and reverse tranases discussed in Chapter 5, as well as to a few RNA polymerases from viruses.
一个血分化体系导致现代DNA聚合酶和反转录酶在第5章所讨论的,以及一些从病毒RNA聚合酶。
The other lineage formed all of the modern RNA polymerases that we discuss in this chapter.
形成的其他家族所有的现代的RNA聚合酶在这一章中讨论。
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