分子生物學(xué)張海紅8章_第1頁
分子生物學(xué)張海紅8章_第2頁
分子生物學(xué)張海紅8章_第3頁
分子生物學(xué)張海紅8章_第4頁
分子生物學(xué)張海紅8章_第5頁
已閱讀5頁,還剩87頁未讀 繼續(xù)免費閱讀

下載本文檔

版權(quán)說明:本文檔由用戶提供并上傳,收益歸屬內(nèi)容提供方,若內(nèi)容存在侵權(quán),請進(jìn)行舉報或認(rèn)領(lǐng)

文檔簡介

1、 第第7章內(nèi)容回顧章內(nèi)容回顧1. 染色體、染色質(zhì)和核小體以及染色體的結(jié)構(gòu)特點。染色體、染色質(zhì)和核小體以及染色體的結(jié)構(gòu)特點。2. dna包裝成染色體的重要性是什么?包裝成染色體的重要性是什么?3. 基因組大小、基因數(shù)量和基因密度的概念?;蚪M大小、基因數(shù)量和基因密度的概念。4. 在真核細(xì)胞中,影響基因密度大小的因素什么?在真核細(xì)胞中,影響基因密度大小的因素什么?5. dna重復(fù)序列的特點和分布。重復(fù)序列的特點和分布。6. 染色體中的哪些元件不參與基因的表達(dá)?染色體中的哪些元件不參與基因的表達(dá)?7. 核小體的組成,組蛋白的結(jié)構(gòu)特點。核小體的組成,組蛋白的結(jié)構(gòu)特點。8. 能夠調(diào)節(jié)染色質(zhì)結(jié)構(gòu)的因素有哪

2、些?能夠調(diào)節(jié)染色質(zhì)結(jié)構(gòu)的因素有哪些? 9. 組蛋白組蛋白n-端尾巴的作用有哪些?端尾巴的作用有哪些?chapter 8:the replication of dnathe structure of dnachapter 8chapter 8 in 1957, m. meselson and f. w. stahl successfully obtained the experimental proof for the semi-conservative replication of dna. they did this by inventing a new technique called d

3、ensity gradient centrifugation. their paper was published in 1958 and ever since, the experiment has often been referred to as: one of the most beautiful experiments in biology. how it began:chapter 8chapter 8meselson and stahl experiment meselson及及stahl:提出半保留模型:提出半保留模型m. meselson and f.w. stahl. 19

4、58. the replication of dna in e. coli. proc. natl. acad. sci. u.s.a. 44: 671-682. semi conservation replicationchapter 8chapter 8meselson and stahl.swfchapter 8chapter 8cscl (氯化銫氯化銫)密度梯密度梯度離心分離度離心分離dnasemi-conservation replication視頻視頻complications of dna replication enzymes the topological problem d

5、irection problem: semi-discontinuously primingchapter 8chapter 8t1: the chemistry of dna synthesist2: the mechanism of dna polymeraset3: the replication fork t4: the specialization of dna polymerases t5: dna synthesis at the replication fork t6: initiation of dna replicationt7: binding and unwinding

6、t8: finishing replicationlecture topicsgeneraldetailedchapter 8chapter 8the first part describes the basic chemistry of dna synthesis and the function of the dna polymerase.chapter 8chapter 8chapter 8chapter 8t1: the chemistry of dna dna synthesis requires deoxynucleoside triphosphates (dntp) and a

7、primer: template junction. dna is synthesized by extending the 3 end of the primer. hydrolysis of pyrophosphate (ppi) is the driving force for dna synthesis.(1) dna synthesis requires deoxynucleoside triphosphates and a primer:template junction chapter 8chapter 8figure 8-1 substrates required for dn

8、a synthesis.dgtp. dctp. datp, or dttpchapter 8chapter 8(2) dna is synthesized by extending the 3 end of the primerfigure 8-2 diagram of the mechanism of dna synthesis.5 3 dna的結(jié)構(gòu)式的結(jié)構(gòu)式chapter 8chapter 8t2: the mechanism of dna polymerase1. dna聚合酶以聚合酶以脫氧核苷酸三磷酸脫氧核苷酸三磷酸(dntps)為)為底物底物,沿模板的,沿模板的35方方向,將對應(yīng)的脫

9、氧核苷酸連接到新生向,將對應(yīng)的脫氧核苷酸連接到新生dna鏈的鏈的3端,端,使新生鏈沿使新生鏈沿53方向方向延長延長。dna polymerase (pol)2. 新鏈與原有的模板鏈新鏈與原有的模板鏈序列序列互補(bǔ)互補(bǔ),亦與,亦與模板鏈的原配對鏈序列一致。模板鏈的原配對鏈序列一致。3. dna聚合酶均以聚合酶均以53方向合成方向合成dna,且均不能且均不能“重新重新”(de novo)合成)合成dna,而只能將脫氧核苷酸加到已有的,而只能將脫氧核苷酸加到已有的rna或或dna的的3端端羥基羥基上。上。 (1) dna pol use a single active site to catalyze

10、 dna synthesis a single site to catalyze the addition of any of the four dntps. recognition of different dntp by monitoring the ability of incoming dntp in forming a-t and g-c base pairs; incorrect base pair dramatically lowers the rate of catalysis. distinguish between rntp and dntp by steric exclu

11、sion of rntps from the active site.chapter 8chapter 8chapter 8chapter 8figure 8-3 correctly paired bases are required for dna-pol-catalyzed nucleotide addition.chapter 8chapter 8figure 8-4 schematic illustration of the steric constraints preventing dna pol from using rntp precurson.distinguish betwe

12、en rntp and dntp by steric exclusion of rntps from the active site.in dna pol, the nucleotide binding pocket is too small to allow the presence of a 2-oh on the incoming nucleotide. this space is occupied by two amino acids (discriminator amino acids辨識氨基酸辨識氨基酸) that make van der waals contacts with

13、the sugar ring.chapter 8chapter 8(2) dna pol resemble a that grips the primer:template junction schematic of dna pol bound to a primer: template junctiona similar view of the t7 dna pol bound to dnafigure 8-5 three-dimensional structure of dna pol resembles a right hand.chapter 8chapter 8figure 8-8

14、illustration of the path of the template dna through the dna pol.thumbfingerspalmchapter 8chapter 8thumbfingerspalm維持引物以及活性部位的維持引物以及活性部位的正確位置;正確位置;幫助維持幫助維持dna聚合酶與其聚合酶與其底物之間的緊密連接。底物之間的緊密連接。一旦引入的一旦引入的dntp與模板之與模板之間形成正確的堿基配對,手間形成正確的堿基配對,手指域即發(fā)生閉合式移動,從指域即發(fā)生閉合式移動,從而包圍住而包圍住dntp,使引入的,使引入的核苷酸與催化的金屬離子密核苷酸與催化的金

15、屬離子密切接觸,促進(jìn)催化反應(yīng);另切接觸,促進(jìn)催化反應(yīng);另外,手指域的移動使模板的外,手指域的移動使模板的磷酸二酯鍵骨架在活性部位磷酸二酯鍵骨架在活性部位后立即產(chǎn)生彎曲,使催化位后立即產(chǎn)生彎曲,使催化位點上引物后第一個模板堿基點上引物后第一個模板堿基暴露,便于與下一個配對堿暴露,便于與下一個配對堿基結(jié)合?;Y(jié)合。手掌域不僅可以催化手掌域不僅可以催化dntp的添加反應(yīng),還可以去除錯配的的添加反應(yīng),還可以去除錯配的dntp;手掌域可以;手掌域可以結(jié)合結(jié)合2個二價金屬離子,從而改變正確堿基配對的個二價金屬離子,從而改變正確堿基配對的dntp和引物和引物3-oh周圍的化周圍的化學(xué)環(huán)境;手掌域還負(fù)責(zé)檢查最

16、新加入的核苷酸堿基配對的準(zhǔn)確性。學(xué)環(huán)境;手掌域還負(fù)責(zé)檢查最新加入的核苷酸堿基配對的準(zhǔn)確性。(3) dna pol are processive enzymes dna聚合酶是一種延伸酶。聚合酶是一種延伸酶。 1)延伸能力是酶處理多聚體底物時的一種特性。)延伸能力是酶處理多聚體底物時的一種特性。 2)dna聚合酶的延伸能力定義為每次酶與引物模板接頭聚合酶的延伸能力定義為每次酶與引物模板接頭結(jié)合時所添加核苷酸的平均數(shù)結(jié)合時所添加核苷酸的平均數(shù)。每個。每個dna聚合酶都有其聚合酶都有其特征性的延伸能力,范圍從每次結(jié)合時的幾個到特征性的延伸能力,范圍從每次結(jié)合時的幾個到5000多多個堿基。個堿基。 d

17、na合成的速率與聚合酶的延伸能力密切相關(guān)。因為,合成的速率與聚合酶的延伸能力密切相關(guān)。因為,聚合酶與引物聚合酶與引物-模板接頭的最初結(jié)合是限速步驟。模板接頭的最初結(jié)合是限速步驟。 chapter 8chapter 8the thumb helps to maintain a strong association between the dna polymerase and its substrate.dna polymerases are processive enzymes; thus the rate of dna synthesis is dramatically increased (

18、1000 bp/sec).chapter 8chapter 8figure 8-9聚合酶與引物聚合酶與引物-模板接頭的最初模板接頭的最初結(jié)合是限速步驟(結(jié)合是限速步驟(1sec)(4) exonucleases proofread newly synthesized dna the occasional flicking of the bases into “wrong” tautomeric form results in incorrect base pair and mis-incorporation of dntp. (10-5 mistake) the mismatched dntp

19、 is removed by proofreading exonuclease, a part of the dna polymerase.how does the exonucleases work? kinetic selectivitychapter 8chapter 8figure 8-10chapter 8chapter 8 proofreading exonucleases removes bases from the 3 end of mismatched dna. proofreading_function.swft1: the chemistry of dna synthes

20、ist2: the mechanism of dna polymeraset3: the replication fork t4: the specialization of dna polymerases t5: dna synthesis at the replication fork t6: initiation of dna replicationt7: binding and unwindingt8: finishing replicationlecture topicsgeneraldetailedchapter 8chapter 8the second part describe

21、s how the synthesis of dna occurs in the context of an intact chromosome at replication forks. chapter 8chapter 8t3: the replication fork the junction between the newly separated template strands and the unreplicated duplex dna. chapter 8chapter 8新分開的模板鏈與未復(fù)制的雙鏈新分開的模板鏈與未復(fù)制的雙鏈dna之間的連接區(qū)稱為復(fù)制叉。之間的連接區(qū)稱為復(fù)制

22、叉。chapter 8chapter 8(1) both strands of dna are synthesized together at the replication fork.figure 8-11leading strand(前導(dǎo)鏈前導(dǎo)鏈)lagging strand(后隨鏈后隨鏈)okazaki fragment(1001000bp)replication fork(2) dna helicases unwind the double helix in advance of the replication forkchapter 8chapter 8figure 8-13dna解

23、旋酶解旋酶分離雙螺旋的兩條鏈。dna解旋酶具有5-3極性。即在后隨鏈上。chapter 8chapter 8(3) single-stranded binding proteins (ssbs) stabilize single-stranded dna cooperative binding sequence-independent manner(electrostatic interactions) figure 8-15單鏈單鏈dna結(jié)合蛋白結(jié)合蛋白(4) the initiation of a new strand of dna require an rna primer primas

24、e is a specialized rna polymerase dedicated to making short rna primers on an ssdna template. do not require specific dna sequence. dna pol can extend both rna and dna primers annealed to dna template chapter 8chapter 8(5) rna primers must be removed to complete dna replication a joint efforts of rn

25、ase h, dna pol & dna ligase figure 8-12 removal of rna promers from newly synthesized dna.chapter 8chapter 8chapter 8chapter 8(6) topoisomerase removes supercoils produced by dna unwinding at the replication forkfigure 8-16chapter 8chapter 8(7) replication fork enzymes extend the range of dna polyme

26、rase dna pol can not accomplish replication without the help of other enzymes t4: the specilization of dna polymeraseschapter 8chapter 8 each organism has a distinct set of different dna pols different organisms have different dna polsdna pol iii holoenzyme: a protein complex responsible for e. coli

27、 genome replicationdna pol i: removes rna primers in e. coli eukaryotic cells have multiple dna pol. three are essential to duplicate the genome: dna pol d d, dna pol e e and dna pol a a/primase. (what are their functions?) pol switching in eukaryotes: the process of replacing dna pol a a/primase wi

28、th dna pol d d or dna pol e e. chapter 8chapter 8chapter 8chapter 8(1) dna polymerases are specialized for different roles in the cellchapter 8chapter 8dna pols of eukaryotes?figure 8-17 dna polymerase switching during eukaryotic dna replicationchapter 8chapter 8 the process of replacing dna pola a/

29、primase with dna pold d or dna pole e. 50100bp10010000bpchapter 8chapter 8(2) sliding clamps dramatically increase dna pol processivity encircle the newly synthesized double-stranded dna and the pol associated with the primer: template junction. ensures the rapid rebinding of dna pol to the same pri

30、mer: template junction, and thus increases the processivity of pol. eukaryotic sliding dna clamp is pcnachapter 8chapter 8figure 8-18 structure of a sliding dna clamp.figure 8-19 sliding dna clamps increase the processivity of associated dna pols.chapter 8chapter 8chapter 8chapter 8figure 8-20 three

31、-dimensional structure of sliding dna clamps isolated from different organism.sliding dna clamps are found across all organism and share a similar structuretwo copies of b proteintrimer of the pcna proteintrimer of the gp45 proteine.coli:eukaryotict4 phagechapter 8chapter 8(3) sliding clamps are ope

32、ned and placed on dna by clamp loaders clamp loader is a special class of protein complex catalyzes the opening and placement of sliding clamps on the dna, such a process occurs anytime a primer-template junction is present. sliding clamps are only removed from the dna once all the associated enzyme

33、s complete their function.chapter 8chapter 8atp control of sliding dna clamp loadingsliding clamp loaderchapter 8chapter 8 at the replication, the leading strand and lagging strand are synthesized simultaneously. to coordinate the replication of both strands, multiple dna pols function at the replic

34、ation fork. dna pol iii holoenzyme is such an example.t5: dna synthesis at the replication forkchapter 8chapter 8composition of the dna pol iii holoenzymefigure 8-21chapter 8chapter 8figure 8-22* trombone modelchapter 8chapter 8chapter 8chapter 8chapter 8chapter 8dna_replication.swf7. rnase h(切除切除rn

35、a引物,引物,dna pol i,dna ligase).(pol iii )interactions between replication fork proteins form the e. coli replisome replisome is established by protein-protein interactions1. dna helicase & dna pol iii holoenzyme, this interaction is mediated by the clamp loader and stimulates the activity of the helic

36、ase (10-fold)2. dna helicase & primase, which is relatively week and strongly stimulates the primase function (1000-fold). this interaction is important for regulation the length of okazaki fragments.chapter 8chapter 8 dna pol iii holoenzyme, helicase and primase interact with each other to form rep

37、lisome, a finely tuned factory for dna synthesis with the activity of each protein is highly coordinated.chapter 8chapter 8interactions between replication fork proteins from the e. coli replisomechapter 8chapter 8figure 8-23 binding of the dna helicase to dna pol iii holoenzyme stimulates the rate

38、of dna strand separation.視頻視頻t1: the chemistry of dna synthesist2: the mechanism of dna polymeraset3: the replication fork t4: the specialization of dna polymerases t5: dna synthesis at the replication fork t6: initiation of dna replicationt7: binding and unwindingt8: finishing replicationlecture to

39、picsgeneraldetailedchapter 8chapter 8the third part focuses on the initiation and termination of dna replication. note that dna replication is tightly controlled in all cells and initiation is the step for regulation. chapter 8chapter 8思考下列概念之間的關(guān)系:思考下列概念之間的關(guān)系: 復(fù)制子(復(fù)制子(replicon) 復(fù)制器(復(fù)制器(replicator) 復(fù)

40、制起始位點(復(fù)制起始位點( origin of replication ) 起始子(起始子(initiator) 起始位點識別復(fù)合體(起始位點識別復(fù)合體(origin recognition complex,orc) 復(fù)制體(復(fù)制體(replisome)chapter 8chapter 8t6: initiation of dna replication(1) specific genomic dna sequences direct the initiation of dna replication origins of replication, the sites at which dna

41、 unwinding and initiation of replication occur. replicator: the entire site of cis-acting dna sequences sufficient to direct the initiation of dna replicationinitiator protein: specifically recognizes a dna element in the replicator and activates the initiation of replicationfigure 8-24 the replicat

42、ion model.chapter 8chapter 8chapter 8chapter 8the identification of origins of replicationbox 8-5 figure 1 genetic identification of replicators (origins)chapter 8chapter 8(2) replicator sequences include initiator binding sites and easily unwound dnafigure 8-25 structure of replication.起始子結(jié)合位點:綠色起始

43、子結(jié)合位點:綠色1)含有起始子蛋白質(zhì)結(jié)合的位點,此位點是組裝復(fù)制起始機(jī)器的核心;2)含有一段富含at的dna,此段dna容易解旋但并不自發(fā)進(jìn)行。在復(fù)制器上,dna的解旋是由復(fù)制起始蛋白控制的,這些蛋白被嚴(yán)格調(diào)控。如在e.coli中,復(fù)制器為“oric”。9核苷酸單位的基序是起始子dnaa的結(jié)合位點,在oric”上重復(fù)5次,13核苷酸單位的基序重復(fù)3次,是起始時單鏈dna形成的起始位點。 促進(jìn)促進(jìn)dna解旋的元件:藍(lán)色解旋的元件:藍(lán)色第一段第一段dna合成的位點:紅色合成的位點:紅色t7: binding and unwinding: origin selection and activatio

44、n by the initiator proteinchapter 8chapter 8 three different functions of initiator protein: (1) binds to replicator, (2) distorts/unwinds a region of dna, (3) interacts with and recruits additional replication factors dnaa in e. coli (all 3 functions), origin recognition complex (orc) in eukaryotes

45、 (functions 1 & 3)figure 8-26 functions of the initiator proteins during the initiation of dna replication.chapter 8chapter 8123chapter 8chapter 8(1) protein-protein and protein-dna interactions direct the initiation process dnaa recruits the dna helicase, dnab and the helicase loader dnac dnab inte

46、racts with primase to initiate rna primer synthesis, see replisome part for more details.figure 8-27 models for e. coli initiation of dna replicationchapter 8chapter 8figure 8-27 models for e. coli initiation of dna replicationchapter 8chapter 8下列概念之間的關(guān)系:下列概念之間的關(guān)系:復(fù)制子(復(fù)制子(replicon)復(fù)制器(復(fù)制器(replicator

47、)復(fù)制起始位點(復(fù)制起始位點( origin of replication )復(fù)制體(復(fù)制體(replisome)起始位點識別復(fù)合體(起始位點識別復(fù)合體(origin recognition complex, orc)起始子(起始子(initiator)dnaprotein(2) eukaryotic chromosome are replicated exactly once per cell cycle, which is critical for these organimschapter 8chapter 81)當(dāng))當(dāng)dna復(fù)制時,必須復(fù)制時,必須激活足夠多的起始位點,激活足夠多的起始

48、位點,以保證每個以保證每個s期中每條染期中每條染色體都被完全復(fù)制;色體都被完全復(fù)制;2)通常一個細(xì)胞周期,起始通常一個細(xì)胞周期,起始位點只被激活一次,位點只被激活一次, 即即復(fù)制只完成一次。如果某復(fù)制只完成一次。如果某些區(qū)域沒有被復(fù)制,就會些區(qū)域沒有被復(fù)制,就會產(chǎn)生染色體斷裂。產(chǎn)生染色體斷裂。 figure 8-29 replicators are inactivated by dna replicationchapter 8chapter 8(3) pre-replicative complex (pre-rc) formation directs the initiation of rep

49、lication in eukaryotes initiation in eukaryotes requires two distinct steps1.replicator selection: the process of identifying sequences for replication initiation (g1 phase), which is mediated by the formation of pre-rcs at the replicator region. 2.origin activation:chapter 8chapter 8figure 8-30 ste

50、ps in the formation of the prerelicative complex (pre-rc)chapter 8chapter 8aaa+aaa+pre-rc的形成并不導(dǎo)致起始的形成并不導(dǎo)致起始位點位點dna立即被解旋或者立即被解旋或者dna聚合酶的募集,而是只聚合酶的募集,而是只有在細(xì)胞從細(xì)胞周期的有在細(xì)胞從細(xì)胞周期的g1到到達(dá)達(dá)s期后,期后,g1期形成的期形成的pre-rc才被激活,并啟動復(fù)制才被激活,并啟動復(fù)制起始。起始。 helicase2.origin activation: pre-rcs are activated by two protein kinases

51、 (cdk and ddk) that are active only when the cells enter s phase.chapter 8chapter 8kinases(激酶):是一類可以將激酶):是一類可以將磷酸基團(tuán)磷酸基團(tuán)共價連接到靶蛋共價連接到靶蛋白上的蛋白質(zhì)。白上的蛋白質(zhì)。所有的激酶在所有的激酶在g1期失活,進(jìn)入期失活,進(jìn)入s期后被激活期后被激活。 assembly of the eukaryotic replication forkchapter 8chapter 8figure 8-31pre-rc(4) pre-rc formation and activation

52、is regulated to allow only a single round of replication during each cell cycle.only one opportunity for pre-rcs to form, and only one opportunity for pre-rc activation.chapter 8chapter 8cdks: cyclin-dependent kinasesfigure 8-32 effect of cdk activity on pre-rc formation and activationchapter 8chapt

53、er 8g1 phases/g2/m phasefigure 8-32 cell cycle regulation of cdk activity and pre-rc formatinchapter 8chapter 8same points between eukaryotic and prokaryotic dna replication initiationchapter 8chapter 81)recognize the replicator (dnaa vs orc ); 2)assembles the dna helicase on the replicator (dnab vs

54、 mcm2-7); 3) helicase generates a region of ssdna for rna primer synthesis; 4) the replisome assembles and start dna replication.different points between eukaryotic and prokaryotic dna replication initiationchapter 8chapter 8in bacteria cells:1) initiate replication more than once per cell cycle;2)

55、focus regulation on the binding of the dnaa initiator protein to the dna . in eukaryotic cells:1) initiate replication only once per cell cycle; 2) focus regulation on the binding of the mcm helicase to the dna . t8: finishing replicationchapter 8chapter 8 dna 復(fù)制的完成需要一系列復(fù)雜的過程,復(fù)制的完成需要一系列復(fù)雜的過程,對于環(huán)形和線性

56、染色體來說,這些過程有所對于環(huán)形和線性染色體來說,這些過程有所不同。不同。 環(huán)形染色體的復(fù)制叉機(jī)器能夠復(fù)制整個分環(huán)形染色體的復(fù)制叉機(jī)器能夠復(fù)制整個分子,但是產(chǎn)生的子代分子之間是相互拓?fù)溥B子,但是產(chǎn)生的子代分子之間是相互拓?fù)溥B接的。接的。 線性染色體最末端處的復(fù)制是通過線性染色體最末端處的復(fù)制是通過端粒酶端粒酶延伸染色體延伸染色體3端端來解決末端復(fù)制的問題。來解決末端復(fù)制的問題。(1) type ii topoisomerases are required to separate daughter dna moleculeschapter 8chapter 8(2) lagging-strand

57、 synthesis is unable to copy the extreme ends of linear chromosomeschapter 8chapter 8fig 8-35end replication problemtelomerestructure of human telomerechapter 8chapter 8 端粒是染色體末端的一種特殊結(jié)構(gòu),是端粒是染色體末端的一種特殊結(jié)構(gòu),是dna與相關(guān)蛋白質(zhì)的復(fù)合與相關(guān)蛋白質(zhì)的復(fù)合體。端粒體。端粒dna由許多短的富含鳥嘌呤(由許多短的富含鳥嘌呤(g)的重復(fù)序列串聯(lián)而成,)的重復(fù)序列串聯(lián)而成,可長達(dá)可長達(dá)10kb以上。人的端粒重復(fù)

58、序列為以上。人的端粒重復(fù)序列為ttaggg,長達(dá),長達(dá)15kb。 端粒主要有兩大生理功能:(端粒主要有兩大生理功能:(1)維持染色體結(jié)構(gòu)的完整性,防止)維持染色體結(jié)構(gòu)的完整性,防止染色體被核酸酶降解及染色體間相互融和。(染色體被核酸酶降解及染色體間相互融和。(2)防止染色體結(jié)構(gòu))防止染色體結(jié)構(gòu)基因在復(fù)制時丟失,解決了末端復(fù)制的難題。基因在復(fù)制時丟失,解決了末端復(fù)制的難題。 figure 4-41 telomeres form a looped structure in the cellchapter 8chapter 8telomerasechromosome duplication & se

59、gregationchromosome duplication & segregation端粒的合成主要依靠端粒的合成主要依靠端粒酶端粒酶來催化。端粒酶是來催化。端粒酶是rna與蛋白質(zhì)組成與蛋白質(zhì)組成的核糖核蛋白,是一種的核糖核蛋白,是一種rna依賴性依賴性dna聚合酶聚合酶。人類端粒酶。人類端粒酶rna成分已被成功克隆,它包括與端粒重復(fù)序列互補(bǔ)的成分已被成功克隆,它包括與端粒重復(fù)序列互補(bǔ)的11個核苷個核苷酸酸5-cuaacccuaac-3。端粒酶的主要作用是維持端粒的長度。它能利用端粒端粒酶的主要作用是維持端粒的長度。它能利用端粒3端單鏈為端單鏈為引物,自身的引物,自身的rna為模板合成端粒

60、重復(fù)序列添加到染色體末端,為模板合成端粒重復(fù)序列添加到染色體末端,從而延長端粒的長度。人的生殖細(xì)胞、造血干細(xì)胞及從而延長端粒的長度。人的生殖細(xì)胞、造血干細(xì)胞及t、b淋巴淋巴細(xì)胞中端粒酶有不同程度的表達(dá),細(xì)胞中端粒酶有不同程度的表達(dá),而在正常的體細(xì)胞中,端粒酶而在正常的體細(xì)胞中,端粒酶處于失活狀態(tài),因此體細(xì)胞隨細(xì)胞分裂次數(shù)的增加端粒逐漸縮短。處于失活狀態(tài),因此體細(xì)胞隨細(xì)胞分裂次數(shù)的增加端粒逐漸縮短。端粒的長度與有絲分裂次數(shù)相關(guān),所以端粒又有細(xì)胞的端粒的長度與有絲分裂次數(shù)相關(guān),所以端粒又有細(xì)胞的“有絲分有絲分裂鐘裂鐘”之稱之稱. telomerase_function.swftelomerase

溫馨提示

  • 1. 本站所有資源如無特殊說明,都需要本地電腦安裝OFFICE2007和PDF閱讀器。圖紙軟件為CAD,CAXA,PROE,UG,SolidWorks等.壓縮文件請下載最新的WinRAR軟件解壓。
  • 2. 本站的文檔不包含任何第三方提供的附件圖紙等,如果需要附件,請聯(lián)系上傳者。文件的所有權(quán)益歸上傳用戶所有。
  • 3. 本站RAR壓縮包中若帶圖紙,網(wǎng)頁內(nèi)容里面會有圖紙預(yù)覽,若沒有圖紙預(yù)覽就沒有圖紙。
  • 4. 未經(jīng)權(quán)益所有人同意不得將文件中的內(nèi)容挪作商業(yè)或盈利用途。
  • 5. 人人文庫網(wǎng)僅提供信息存儲空間,僅對用戶上傳內(nèi)容的表現(xiàn)方式做保護(hù)處理,對用戶上傳分享的文檔內(nèi)容本身不做任何修改或編輯,并不能對任何下載內(nèi)容負(fù)責(zé)。
  • 6. 下載文件中如有侵權(quán)或不適當(dāng)內(nèi)容,請與我們聯(lián)系,我們立即糾正。
  • 7. 本站不保證下載資源的準(zhǔn)確性、安全性和完整性, 同時也不承擔(dān)用戶因使用這些下載資源對自己和他人造成任何形式的傷害或損失。

評論

0/150

提交評論