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02 Cells and Tissues 细胞和组织3 k3 f3 [7 r; ^% X
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#04-05 Transcription and translation 转录和翻译
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在线视频 http://v.youku.com/v_show/id_XNDI2NjI2OTQyMA==.html
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, ?$ @2 d/ u! D, o- p u#04 Transcription 转录9 ] P( K1 v' R7 c/ |+ a
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All cellular gene expression and protein building occurs through the two principal steps called transcription and translation.
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所有细胞基因表达和蛋白质构建,主要通过两个步骤,称为转录和翻译。) L' i" L: t, ?! H9 U
$ T2 g& }; B; s- P: aIn transcription, DNA’s information is encoded or “transcription” into messenger RNA or mRNA. The process begins when RNA polymerase opens the double helix of DNA, like the slider on a zipper. It unwinds the DNA double helix and pries the two DNA strands apart. As the RNA polymerase continues down the length of the DNA, several actions take place.
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' f3 F' a. j% k' |. v. ^; r% ~转录时,DNA的信息被编码或“转抄”到信使RNA或mRNA内。这一过程开始于RNA聚合酶打开的双螺旋之时,就像一条拉链的拉头。将DNA双螺旋解旋,将两条DNA链撬开。随着RNA聚合酶继续缩短DNA的长度,发生了几种作用。+ c! B5 r5 R2 Q+ U7 m
: N1 j+ Z5 `4 s4 {! tIt reads one strand of the DNA and transcribes the DNA’s information. It creates an mRNA version of the DNA or “transcript”. The mRNA transcript is a complementary copy of the DNA sequence. When the transcription ends and the mRNA template is complete, it separates from the DNA template, and exits the nucleus through pores. The template enters the cytoplasm on its way to the next step in the process of polypeptide synthesis: translation. 3 [2 ~ o/ }8 F9 B8 Q. E# {0 t
- J+ T# e9 q1 D4 B+ K, f只读取一条DNA链并转录DNA信息,构成DNA或“转录本”的mRNA版本。mRNA转录本是DNA序列的互补副本。转录结束,mRNA模板完成后,便从DNA模板分离,通过核孔退出细胞核。模板进入胞质内,接着下一步称为多肽合成的过程:翻译。$ g2 a$ y. Q# v! q. Z* a& t
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#05 Translation 翻译( x! i, W+ t/ ^* X7 n5 k% c) S
8 Q, h2 W6 Q2 X4 M2 tTranslation begins when the mRNA enters the cytoplasm and a small ribosomal subunit attaches itself to the end of the mRNA strand. At the same time, a transfer RNA (tRNA) molecule recognizes and binds to the “start” codon on the mRNA strand. tRNA recognizes the mRNA codon through its “anticodon”, which has a sequence complementary to the mRNA codon. It is the tRNA molecules that carry the amino acid building blocks of the protein.
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% z$ z, Z) s/ P翻译开始于mRNA进入胞质时,小型核糖体亚单位附着于mRNA链的末端,与此同时,转运RNA分子识别mRNA链上的“启动”密码子并与之结合。tRNA通过自身具有与mRNA密码子互补的“反密码子”序列来识别mRNA,这种tRNA分子携带构建蛋白块的氨基酸。. U! ]5 N/ }# [& i
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Next, a large ribosomal subunit joins and forms the fully functional ribosome that will join the amino acids on the tRNAs to synthesize the protein. When the amino acids of the two tRNA molecules are joined, the tRNA in the first position is released to get a new amino acid. The growing protein is attached to the tRNA in the second position.( w: |5 ]! c9 j" I8 Q, B0 C
, T9 }) ~! D5 O下一步是大型核糖体亚单位联结,形成功能完整的核糖体,与tRNA上的氨基酸联结合成蛋白质。当两个tRNA分子的氨基酸联结后,第一个位置上的tRNA便释放,获取一个新的氨基酸。长出的蛋白质附着于第二个位置的tRNA。# ]" W2 Y* I; Y% m9 w+ I" V
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The mRNA is then pulled through the ribosome so that the tRNA with the protein chain is now in the first position. Now a new tRNA with the proper anticodon can come into the ribosome at the open position. This pattern continues as tRNA after tRNA bind to the mRNA codons and their amino acids are added to the growing protein chain. Toward the end of the mRNA sequence, the ribosome gets to a “stop” codon, which does not code for any amino acid. This signals the end of the protein and that the translation process is complete.
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6 ^# ]* A0 c$ f' z- {2 i然后mRNA从核糖体拉出,带有蛋白链的tRNA便位于第一个位置。带有正确反密码子的新tRNA便在开放位置进入核糖体。这一方式不断继续,tRNA接着tRNA与mRNA密码子结合,其氨基酸加入生长中的蛋白质。在这个mRNA序列的末端,核糖体得到“停止”密码子,此密码子并不编码任何氨基酸。这标志着蛋白质的末端,说明翻译转录过程已经完成。) a" F( c. Z; ?
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The ribosome then releases the finished protein from the tRNA, and detaches from the mRNA as the two ribosomal subunits separate. The protein will then be further modified in other cellular structures or directly used by the body.: l Y. m2 _% w6 d# c
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之后核糖体从tRNA释放已经完成的蛋白质,并随着两个核糖体亚单位分离,从mRNA脱离。蛋白质在其他细胞结构内进一步修饰,或者直接被机体利用。
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