1、會計學1生物信息學分子生物學中心法則生物信息學分子生物學中心法則ReplicationReplication，復制：在親代，復制：在親代DNADNA雙鏈的每一條鏈上按堿基雙鏈的每一條鏈上按堿基配對而準確地形成一條新的配對而準確地形成一條新的互補鏈，結果生成兩個與親互補鏈，結果生成兩個與親代鏈相同的代鏈相同的DNADNA雙鏈。雙鏈。在在DNA復制時，親代復制時，親代DNA的雙螺旋先解旋，然后以每條的雙螺旋先解旋，然后以每條鏈為模板，按照堿基配對原則，在這兩條鏈上各形成一條鏈為模板，按照堿基配對原則，在這兩條鏈上各形成一條互補鏈。在每一個新形成的雙螺旋中，一條鏈是從親代互補鏈。在每一個新形成的雙螺

2、旋中，一條鏈是從親代DNA來的，另一條是新形成的。來的，另一條是新形成的。355 33 5533553leading strand (synthesized continuously)lagging strand (synthesized discontinuously)Each replication fork has a leading and a lagging strand The leading and lagging strand arrows show the direction of DNA chain elongation in a 5 to 3 direction The

3、small DNA pieces on the lagging strand are calledOkazaki fragments (100-1000 bases in length)replication forkreplication forkRNA primer533535direction of leading strand synthesisdirection of lagging strand synthesisreplication fork5353Movement of the replication forkMovement of the replication forkR

4、NA primerOkazaki fragmentRNA primer5在DNA復制過程中，由眾多的酶和蛋白質參與DNA的復制作用。復制體的基本活動包括：1）雙鏈的解開；2）RNA引物的合成；3）DNA鏈的延長；4）切除RNA引物，填補缺口，連接DNA片段；5）切除和修復錯配堿基。Transcription，轉錄：以DNA為模板，按堿基配對將其中所含的遺傳信息傳給RNA，形成一條與DNA鏈互補的mRNA鏈的過程。編碼鏈，有義鏈模板鏈，無義鏈1）RNA聚合酶與DNA模板的結合TranscriptionRNA polymerase,RNA聚合酶聚合酶closed promoter complex,

5、封閉的啟動子復合物封閉的啟動子復合物open promoter complex,開放的啟動子復合物開放的啟動子復合物initiationelongationterminationRNA productRNA chains are synthesized in a 5 to 3 directionProkaryotic RNA polymerase structureRNA polymerase of E. coli is a multisubunit proteinSubunitNumberRole a a 2uncertain b b 1forms phosphodiester bonds

6、b b 1binds DNA template s s 1recognizes promoter and facilitates initiationa a2 2bbbbs sa a2 2bbbb + s sholoenzyme core polymerase sigma factorRNA polymerase holoenzyme (+ s s factor) closed promoter complex (moderately stable) the sigma subunit binds to the -10 region once initiation takes place, R

7、NA polymerase does not need very high affinity for the promoter sigma factor dissociates from the core polymerase after a few elongation reactions elongation takes place with the core RNA polymerase open promoter complex (highly stable) the holoenzyme has very high affinity for promoter regions beca

8、use of sigma factors s sigma can re-bind other core enzymesThe sigma cycles ss s三聯體密碼子的特點：三聯體密碼子的特點：1）方向性）方向性2）無標點性）無標點性3）簡并性）簡并性4）通用性）通用性5）擺動性）擺動性起始密碼子：ATG。終止（無義）密碼子：UAAUGAUAG。同義密碼子：編碼同一個氨基酸的幾個密碼子。Translation，翻譯：在RNA控制下，根據核酸鏈上每三個核苷酸決定一個氨基酸的三聯體密碼規則，合成出具有特定氨基酸順序的蛋白質肽鏈的過程。Protein Synthesis and Protein

9、 Processinga). RNA structureb). Protein synthesisi). Initiation of protein synthesisii). Peptide bond formation; peptidyl transferaseiii). Elongation and termination類型結構作用mRNA信使RNA單鏈；原核生物的mRNA為多順反子，真核生物的為單順反子。DNA原始遺傳信息的直接接受者；合成蛋白質直接模板。tRNA轉運RNA二級結構是三葉草型結構；三級結構為倒L型結構。轉運氨基酸到核糖體上；通過反密碼子識別mRNA上的密碼子。rRNA

10、核糖體RNA16S (small ribosomal subunit)23S (large ribosomal subunit)5S (large ribosomal subunit)含量大，維持核糖體的空間結構；使mRNA和tRNA結合在適當位置；識別mRNA上的啟動和終止信號。核糖體是蛋白質生物合成的場所；核糖體是蛋白質生物合成的場所；mRNAmRNA是合成的模板；是合成的模板；tRNAtRNA是模板與是模板與“合成原料合成原料”氨基酸之間的接合體。氨基酸之間的接合體。 原核生物的核糖體為70S，由50S和30S的大小亞基組成；真核生物的核糖體為80S，由60S和40S的大小亞基組成。rR

11、NA是構成核糖體的骨架。是構成核糖體的骨架。16S (small ribosomal subunit)23S (large ribosomal subunit)5S (large ribosomal subunit)Ribosome structureAP PPPPPPPP-sitepeptidyl tRNA siteA-siteaminoacyl tRNA sitemRNA5Small subunit(40S)Large subunit(60S)Ribosome with bound tRNAs and mRNAa.a. +tRNA+ATP氨酰-tRNA+AMP+PPi氨酰氨酰-tRNA合成

12、酶合成酶氨酰-tRNA合成酶能識別tRNA，并催化反應。對L-氨基酸有極高的專一性，每種氨基酸都有一個專一的酶。氨酰-tRNA合成酶的高度專一性，防止在蛋白質合成時錯誤的氨基酸摻入多肽。Tertiary structureSecondary structuretRNA一個新生肽鏈的誕生，除了必須有mRNA模板，tRNA及核糖體外，還需要許多蛋白因子。如，起始因子(IF)，延長因子(EF)和終止因子(RF)等的參與。肽鏈合成的方向是N-C,mRNA信號被轉譯的方向是5-3。mRNA5 cap40S subunitMeIF2AUGInitiator tRNA bound to thesmall r

13、ibosomal subunit with theeukaryotic initiation factor-2 (eIF2)Initiation of protein synthesis: mRNA bindingThe small subunit finds the 5 cap andscans down the mRNA to the first AUG codonmRNA5 40S subunitMeIF2AUG the initiation codon is recognized eIF2 dissociates from the complex the large ribosomal

14、 subunit binds60S subunitmRNA5 MAUG aminoacyl tRNA binds the A-site first peptide bond is formed initiation is completeGCCAmRNA5 MAUG GCCA氨酰-tRNA NH2 CH3-S-CH2-CH2-CH O=CPeptide bond formation peptide bond formation is catalyzed by peptidyl transferase(肽基轉移酶肽基轉移酶) peptide bond formation results in a

15、 shiftof the nascent peptide from the P-siteto the A-site NH2 CH3-S-CH2-CH2-CH O=C O tRNA NH2CH3-CH O=C O tRNANCP-siteA-site OH tRNA NHCH3-CH O=C O tRNAP-siteA-sitePUCAPPPPPUCA GCA GGG UAGAPPPPElongationGCA GGG UAG following peptide bond formationthe uncharged tRNA dissociatesfrom the P-site the rib

16、osome shifts one codon alongthe mRNA, moving peptidyl tRNAfrom the A-site to the P-site; thistranslocation requires theelongation factor EF2 the next aminoacyl tRNA thenbinds within the A-site; this tRNAbinding requires the elongationfactor EF1EF1EF2 energy for elongation is provided bythe hydrolysi

17、s of two GTPs: one for translocation one for aminoacyl tRNA bindingPUCA GCA GGG UAGPPPPTermination when translation reaches the stopcodon, a release factor (RF) bindswithin the A-site, recognizing thestop codon release factor catalyzes the hydrolysisof the completed polypeptide fromthe peptidyl tRNA

18、, and the entirecomplex dissociatesRFPUCA GCA GGG UAGPPPPPPP內含子內含子外顯子外顯子 遺傳功能的單位，它是一段編碼蛋白質或RNA分子的DNA序列。 執行生物功能的最重要的生物大分子之一，它是單鏈狀分子，由20種不同的氨基酸組成。DNADNARNAcDNA新生肽蛋白質按基因編碼的信息在生物體內合成蛋白質的過程基因調控網絡基因調控網絡NU去折疊重折疊ReplicationReplication，復制：在親代，復制：在親代DNADNA雙鏈的每一條鏈上按堿基雙鏈的每一條鏈上按堿基配對而準確地形成一條新的配對而準確地形成一條新的互補鏈，結果生成兩個與親互補鏈，結果生成兩個與親代鏈相同的代鏈相同的DNADNA雙鏈。雙鏈。RNA polymerase holoenzyme (+ s s factor) closed promoter complex (moderately stable) the sigma subunit binds to the -10 region once initiation takes place, RNA polymerase does not nee