《中山大学生命科学院生物化学课件：RNA Metabolism》由会员分享，可在线阅读，更多相关《中山大学生命科学院生物化学课件：RNA Metabolism（89页珍藏版）》请在金锄头文库上搜索。
1、RNA MetabolismWhat differences between DNA and RNA? Hydroxyl group at the 2 position of Pentose Uracil for thymine Single strands Only macromolecule known to function both in the storage and transmission of information and in catalysisThree major kinds of RNA Messenger RNA encode the amino acid sequ
2、ence of one or more polypeptides specified by a gene or set of genes. Transfer RNA reads the information encoded in the mRNA and transfers the appropriate amino acid to a growing polypeptide chain during protein synthesis. Ribosomal RNAs are constituents of ribosomes where proteins are synthesized.W
3、hat will we discuss?1. RNA synthesis on a DNA template 2. Post synthetic processing 3. RNA dependent synthesis of RNA and DNA1.Transcription: DNA-dependent synthesis of RNA (转录转录) The process by which parts of genetic message encoded in DNA are copied precisely into RNA.RNA is synthesized by RNA pol
4、ymeraseAbout 17bp are unwound at any given timeTemplate strand and nontemplate strand(coding strand)Adenovirus genome RNA polymerase requires DNA for activity and is most active when bound to a dsDNA. Only one of the two DNA strands serves as a template. The template DNA strand is copied in 3 5 dire
5、ction. Each nucleotide in the newly formed RNA is selected by base-pairing interactions. RNA polymerase does not require a primer to initiate synthesis. RNA polymerase lacks a proofreading 3 5 exoneuclease activity. Mistake :10-4 10-5Features of transcription by RNA polymeraseRNA polymerase in E. co
6、liRNA polymerase in E. coliRNA synthesis is initiated at promoters RNA polymerase binds to specific sequences in the DNA called promoters, which direct the transcription of adjacent segments of DNA (genes). Promoter region extends between position -70 and +30Typical E. coli promoters recognized by a
7、n RNA polymerase holoenzyme-40 -60 -35区的序列与起始点的辨认有关,称为辨认结合位点 -10区的序列称为Pribnow盒 (box) 开链位点 The efficiency which an RNA polymerase binds to and initiates transcription at a promoter is determined in large measure by these sequences, the spacing between them, and their distance from the transcription s
8、tart site.RNA polymerase leaves its footprint on a promoterSteps in the initiation of transcription by E. coli RNA polymerase原原 核核 生生 物物 转转 录录 起起 始始Transcription is regulated Occur at any step in transcription. Much of the regulation is directed at the polymerase binding and transcription initiation
9、 steps. Differences in promoter sequences are just one of several levels of control.Specific sequences signal termination of RNA synthesisE.coli has at least two classes of termination signals (rho)-independent terminators have two distinguishing features. The first is a region whose RNA transcript
10、has self-complementary sequences,permitting the formation of a hairpin structure (disrupt the RNA-DNA hybrid and/or he interactions between the RNA and the polymerase). The second feature is a short string of adenylates in the template strand (U in RNA, A:U hybird is relatively unstable) -dependent
11、terminators: hairpin structureA model for independent termination of transcription transcription processTranscription resembles replication Fundamental chemical mechanism Polarity (direction of synthesis) Use of a templateTranscription differs from replication It does not require a primer. Only limi
12、ted segments of a DNA molecule are involved. Within transcribed segments only one DNA strand serves as a template.复 制转 录模 板两股链均复制模板链复制 原 料dNTPNTP酶DNA-polRNA-pol 特 点半保留复制不对称转录产 物子代双链DNAmRNA, tRNA, rRNA配 对A-T, C-GA-U, C-G, T-A引 物需要不需要合成链方向5 35 3复制和转录的异同点(特点)Eukaryotic cells have three kinds of nuclear
13、 RNA polymerases（A）（B）（C）定位核 仁核 质核 质转录产物5.8S、18S、 28SrRNAhnRNA (hetero- geneous nuclear RNA) mRNAtRNA、 5SrRNA对鹅膏蕈碱耐受极敏感中度敏感Common sequences in promoters recognized by eukaryotic RNA polymerase IIThe TATA box is the major assembly point for the proteins of the preinitiation complexes of RNA polymeras
14、e II. The DNA is unwound at the initiator sequence, and the transcription start site is usually within or very near this sequence.cis-acting element (顺式作用元件)* Basal promoter (基本启动子） TATA box or Goldberg-Hogness box ( TATAAA) * Initiator (Inr)（起始子） * Upstream element（上游元件） CCAAT box (TGGN6GCCA) GC bo
15、x(GGGCGG) for Sp1 Octamer (ATGCAAAT) for Oct-1 and Oct-2 * Response element（应答元件）RNA polymerase II requires many other protein factors for its activityTrans-acting factor (反式作用因子) Basal transcription factors required at every RNA polymerase II promoter (designated TFII with an additional identifier, TFIIA, TFIIB) Transcription ancillary factors（转录辅助 因子） 真核生物的转录起始 * 顺式作用元件(cis-acting element) -35区: TATA盒 (Hogness盒) -40-110区: CAAT盒 GC盒 * 反式作用因子(trans-acting factor)- 转录因子（） 转录因子和真核生物的转录起始复合物 * 、H* 起始前复合物（）真核生物转录起始真核生物转录起始Transcription at RNA polymerase II promotersDNA-dependent RNA polyme
