现代分子生物学之转录剪切.pptxVIP

基因的物质状态：DNA上的一个片段DNA本身的结构（为什么可以作为遗传物质）DNA在细胞中的存在形式（染色质、染色体、基因组的特点）DNA的传代方式：复制DNA在传代及储存过程中可能遇到的问题及其解决方式DNA并非静态存储：同源重组是修复方式和减数分裂之必须；CSSR与转座是不同DNA间的剪切融合---DNA分子大尺度改变的基础基因表达：DNA序列影响细胞结构功能RNA的合成：合成工具、基本过程、原核真核异同、后处理蛋白质的合成：密码、合成工具、基本过程、原核真核异同基因表达的调控：基本的原则和方法、原核真核异同基因研究技术问题： 剪接、自剪接与可变剪接的分子机制是什么？它们在生命体系中的地位如何？分子生物学的主要脉络：中心法则课程目标：掌握主要脉络、熟悉基本概念、了解细枝末节 RNA SplicingIntron number in different organismsTHE CHEMISTRY OF RNA SPLICINGSequences within the RNA determine where splicing occursThe consensus sequences for human5’ splice site: the exon-intron boundary at the 5’ end of the intron3’ splice site: the exon-intron boundary at the 3’ end of the intronBranch point site: an A close to the 3’ end of the intron, followed by a polypyrimidine tract (Py tract).The intron is removed as a “Lariat”Two successive transesterification:Step 1: The OH of the A at the branch site attacks the phosphoryl group of the G in the 5’ splice site. -- the 5’ exon is released and the 5’-end of the intron forms a three-way junction structure.Three-way junction Step 2: The OH of the 5’ exon attacks the phosphoryl group at the 3’ splice site. --------- the 5’ and 3’ exons are joined and the intron is liberated in a “lariat”.Can be other exonsTrans-splicing: two exons carried on different RNA molecules can be spliced togetherComplexes of RNAs (snRNA:small nuclear RNA:U1, U2, U4-6, 100-300 nt, by RNA POL III) and proteins (~ 150 proteins)Small nuclear ribonuclear proteins (snRNPs, “snurps”).The spliceosome is the largest snRNP, and the exact makeup differs at different stages of the splicing reactionThree roles of snRNPs in splicing1. Recognizing the 5’ splice site and the branch site.2. Bringing those sites together.3. Catalyzing (or helping to catalyze) the RNA cleavage.Mechanisms: RNA-RNA, RNA-protein and protein-protein interactionsPre-mRNA splicing is carried out by a large complex -- spliceosomeNucleotide Excision Repair: Functions of initiator protein:binds to replicator,distorts/unwinds a region of DN