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T CHC PHN T CA NHIM SC THNhm 3: Trng Xun LcTn N Hong PhngPhm Th Thanh HngNguyn Th TuytI. KHAI NIM V NHIM SC TH (NST)NST la c s di truyn cp t bao. La cu truc nm trong nhn t bao, co kha nng bt mau c trng vi cac phm nhum kim tinh. Mi loai sinh vt co b NST c trng v hinh dang, kich thc, s lng va c duy tri n inh qua cac th h.

Hinh dang NSTII. CU TRUC NST CUA PROKARYOTE Sinh vt nhn s (Prokaryote) la nhom sinh vt ma t bao khng co mang nhn, do nhn khng c hnh dng c nh vng nhn. Khi nhum mu t bo bng thuc nhum Feulgen, vng nhn hin mu tm. Nhim sc th cha 1 si ADN dng vng xon kp ( X khunStreptomycesc th gp nhim sc th dng thng). NST ca prokaryotec kch thc thay i t 160.000 cp base vi khunCandidatus Carsonella ruddiin 12.200.000 cp base vi khun sng trong t Sorangium Cellulosum.Mt s vi khun nhBorrellia (Xon khun gybnh Lyme) c cha nhim sc th tuyn tnh (linear chromosome).

Linear choromosome loi Borrelia burgdorferi NEU2011

Loi ny c 12 NST tuyn tnh v 9 plasmid trn.5- Vi khun Escherichia coli la i tng c s dung rng rai trong cac nghin cu di truyn phn t.

Vi khun Escherichia coli

III. CU TRUC NST CUA EUKARYOTE1. Cu truc hin vi cua NSTMi NST gm 2 cromatic gn vi nhau tm ng, mi cromatic cha 1 phn t ADN. Mi NST in hinh u cha cac trinh t nucleotit c bit c goi la tm ng va cac trinh t nucleotit 2 u cung cua NST c goi la u mut va trinh t khi u nhn i ADN.

-Cac NST thng khac nhau v vi tri tm ng (centromere), la ni cac si thoi v sc bam vao trong qua trinh phn bao.Cac tm ng co ban cht la ADN va kinetochore bam quanh no co ban cht protein. S kt hp cua 2 thanh phn nay tao thanh 1 cu truc ng hoc tham gia vao cac khia canh thit yu cua vic di chuyn ca NST v cac t bao con trong qua trinh phn bao.Mi NST thng chi co mt eo tht ln cha mt tm ng goi la eo s cp (primary constriction) NST thanh 3 kiu chinh:+ NST tm gia+ NST tm u+ NST tm mut Ngoai eo s cp ra thi trn mt s NST cu th con co eo th cp (secondary constriction), nu eo nay nm gn u mut va xay ra s tht su se tao nn 1 v tinh (satellite) cua NST ( ngi o la cac NST 13, 14, 15, 21 va 22). Eo th cp thng cha cac gen tng hp cac ARN ribosome, tich tu tam thi va hinh thanh nn t chc goi la hach nhn. Cu truc u mut cua NST (telome)- Trn mi NST co cac u mut vi cu truc c trng goi la telomere, cac telomere khng cha cac gen, chung gm nhng trinh t ngn (6-8 bp) lp lai ni tip ca ngan ln va co tinh bao tn cao trong tin hoa.Vi du: Tetrahymena: (TTGGGG)nCaenorhabditis: (CCCTCCC)n ngi va cac ng vt co vu cac oan lp ni tip (1.000- 2.000 ln) cua telomere nh sau: 5-TTAGGG-3 - Cac trinh t u mut kt hp vi nhiu loai protein c trng tao thanh cu truc dang vong va co cac chc nng quan trong nh: n inh va bao v cac u mut cua NST va c xem la ng h nguyn phn, gii han s phn chia cua cac t bao soma trong khoang 40-50 ln.Cac tm ng va u mut cua NST eukaryote c cu truc vi nhng trinh t n gian, c lp lai rt nhiu ln goi la ADN v tinh hay ADN lp lai kiu ni tip.- Mi NST eukaryote la mt phc hp nucleoprotein bao gm 1 phn t AND si kep mach thng kt hp vi cac phn t protein c s goi la histone (giau cac aminoacid lysine va arginine) (2H2A, 2H2B giu lysin, 2H3 v 2H4 giu Arginin. ), phc hp nh th goi la cht nhim sc (chromatin).2. Cu truc siu hin vi- n vi t chc c s cua cac NST eukaryote la cac nucleosome , mi nucleosome co ng kinh khoang 11 nm, gm 1 khi cu 8 phn t histon, (H2A+H2B+H3+H4)2 goi la loi octamer va oan ADN co kich thc 146 bp, qun vong xung quanh no ( ni chung l 1 oan ADN dai 160- 200 bp qun 2 vong quanh octamer).- Mt phn t H1 bam vao oan ADN ni gia 2 nucleosom dai khoang 150 bp, gi vng s tng tac cua ADN vi cac histon loi.

- Bc cu truc u tin cua chromatin c hinh dung di dang mt chui cac nucleosome, hay si nucleosome co day 11nm hay ( 110 A0).3. Bn bc cu truc siu hin vi cua NST- Bc th 2 cua NST la s cun gp chromatin co lin quan n s xon lai cua si nucleosome thanh si day 30nm goi la 1 solenoid. Cac histon H1 tham gia vao s xon lai nay bng cach tng tac vi cac phn t H1 khac.Bc th 4 cua NST: cac day euchromatin c sp xp trong cac khng gian 3 chiu xon cht lai tao thanh cac vung goi la heterochromatin trn 1 chromatid vi day 700nm.- Bc th 3 cua NST la s cun vong cua si solenoid thanh 1 cu truc xon hn vi cac vong c neo dinh vao 1 gia trung tm ( day 300nm). => y chinh la vung thao gian xon cua NST, goi la euchromatic.

Nh vy, s khac nhau c ban gia cu truc NST vi khun va eukaryote la:+ sinh vt nhn s cha co cu truc NST in hinh, NST cua vi khun thng la 1 phn t ADN dang vong cha 1 si ADN xon kep ( AND khng co s kin kt vi protein loai histon) va s lng it.+ sinh vt nhn thc a co cu truc NST in hinh, s lng ADN nhiu va dang xon kep, a lin kt vi protein loai histon. ADN l cht trng phn (polymer) sinh hc, c trng lng phn t ln, gm nhiu n phn ni vi nhau thnh cc mch (chui) di. n phn to nn cc axit nucleic l bn loi nucleic, trong ADN l cc n deoxyibonucleotid.- Mi nucleotid gm 3 thnh phn: nhm phosphat, ng pentose v mt trong bn loi bazo nito (cc dn xut purin hoc pyrimidin).- Mi bazo nito gn vi dezoxiibo c gi l nucleozit. Khi c mt gc axit photphoric gn vo nucleozit th s thnh mt nucleotit.- Cc nucleozit ng vi cc bazo c trong thnh phn ca chng, c gi l xitidin, timidin, adenozin v guanozin. Cc nucleotide tng ng c gi l xitidin, timidin, adenin, guanin.

IV. T CHC TRT T NUCLEOTIDE TRONG ADN

- C 4 loi nucltit l A, T, G, X, chng phn bit nhau v baz nit nn ngi ta gi tn ca cc nucltit theo tn ca cc baz nit ( A = Anin, T = Timin, G = Guanin v X = Xitzin).

Cc nucltit trn mt mch lin kt vi nhau bng lin kt phtphoieste to thnh chui plinucltit (lin kt phosphodieste gia gc ng ca nucleotide ny vi gc phosphate ca nucleotide tip theo). Cc nucltit gia 2 mch lin kt vi nhau bng lin kt hir theo nguyn tc b sung (A ca mch ny lin kt vi T ca mch kia bng 2 lin kt hir v ngc li; G ca mch ny lin kt vi X ca mch kia bng 3 lin kt hir v ngc li). Lin kt chnh l lin ktphotphodieste.V 2 nucleeooti ni vi nhau bng lin kt cng ha tr phosphoeste, y l lin kt CHT gia 2 Nu ng k nhau: Axit phosphoric ca Nu ny lin kt vi ng deoxyribose ca Nu bn cnh v tr C3'.Nh vy 1 phn t axit phosporic thc hin 2 lin kt cng ha tr este phospho vi 2 phn t ng deoxyribose. N mi gi lphotphodieste.- Lin kt th nht l lin kt CHT trong cng 1 Nu: Axit phosphoric ca Nu lin kt vi ng ca Nu ti v tr C5'. Gi l lin kt CHT este phosphoni phn t nucleeootit.- Lin kt th hail lin kt CHT gia 2 nucleeooti ng k nhau trong cng mch n: Axit phosphoric ca Nu ny lin kt vi ng ca Nu khc, bn cnh ti v tr C3'. Gi l lin kt CHT este phospholin phn t nucleeootit.29

Cc lin kt phtphodieste gia cc nucltit trong chui plinucltit l cc lin kt bn vng, ch nhng tc nhn t bin c cng mnh mi c th lm nh hng ti lin kt ny do lin kt phtphodieste gi cho phn t ADN s bn vng nht nh. Ngc li, lin kt hir l lin kt yu nhng ADN c rt nhiu lin kt hir nn ADN va bn vng va linh hot, chnh nh tnh linh hot ny m cc enzim c th sa cha cc sai st v trnh t sp xp cc nucltit.

Do cu to ho hc ca cc nucleobase m lin kt hydro ch hnh thnh gia 2 loi nucleobase nht nh l A vi T (qua 2 lin kt hydro) v C vi G (bng 3 lin kt hydro). thc cht l lin kt gia mt purine v 1 pyrimidine nn khong cch tng i gia 2 chui polynucleotide c gi vng. Nguyn tc hnh thnh lin kt trn c gi l nguyn tc b sung v n ph bin trn mi loi sinh vt.Trong t bo, di tc dng ca mt s protein c hiu, 2 chui ca phn t ADN c th tch nhau ra (cn gi l bin tnh ADN) do cc lin kt hydro b ct t. Khi , cc nucleotide trn mi chui c th to thnh lin kt vi cc nucleotide t do trong mi trng ni bo. Kt qu ca qu trnh ny l to thnh 2 phn t ADN ging ht nhau t 1 phn t ADN ban u. y cng chnh l ngun gc ca c tnh di truyn ca sinh vt. Cc nh khoa hc c th thc hin qu trnh t nhn i ny trong ng nghim gi l k thut PCR. Nu s bt cp gia nucleotide chui gc vi nucleotide khng tun theo nguyn tc b sung th s to thnh t bin, ngun gc ca hin tng bin d.

- Trnh t Nucleotit ca gen cu trc qui nh trnh t axit amin ca chui polipeptit.Nhm Eukaryote tin ho hn vi c im:99% genome nm trong nhn TB. Phn cn li nm trong mt s c quan t (ty th, lp th). + B gen t bo cht gm cc ADN si kp, vng. + B gen trong nhn cha nhiu NST.Trong t bao eukaryote, DNA kt hp cht che vi cc protein la histone.Cac DNA eukaryote co c im khac vi DNA prokaryote. Toan b phn t DNA prokaryote u mang thng tin ma ha cho cac protein trong khi o DNA ca eukaryote bao gm nhng trinh t ma ha (cac exon) xen ke vi nhng trinh t khng ma ha (intron).

3. Cc yu t di truyn vn ng prokaryote v eukaryote2. S pht hin cc yu tdi truyn vn ng1. Khi nim4. Cc yu t di truyn vn ng ngi421. Khi nim

- Yu t di truyn vn ng (transposatic genetic elements) hay cn gi l gen nhy l on nucleotit c kh nng di chuyn v tr ngay trong mt th nhim sc hoc t th nhim sc ny sang th nhim sc khc. - Gen nhy c vai tr trong s ti t hp li h gen.

2. S pht hin yu t di truyn vn ng

- Barbara McKlintock pht hin v nghin cu v cc yu t di truyn vn ng trn cy ng t nhng nm 40 ca th k XX. Vo nm 1983 b nhn c gii thng Nobel.- Gery Fink v cs. l nhng ngi u tin s dng nm men nghin cu iu ho hot tnh gene eukaryote.- Vo nm 1985, J.Bocke v G. Fink chng minh, yu t Ty1, ging vi retrovirus.

- Cc yu t di truyn vn ng c tm thy vi khun, nm, thc vt, ng vt v con ngi.

- n nhng nm 70 - 80 vi s tin b ca k thut phn tch di truyn ngi ta mi hiu r c cu trc v c ch hot ng ca cc yu t di truyn vn ng.443. Cc yu t di truyn vn ng prokaryote v eukaryote

Trnh t on xenGen nhyC ch ca s chuyn vYu t TnA

Yu t di truyn vn ng prokaryote Cc retrotransposonDNA transposonYu t di truyn vn ng eukaryote 3.1.Yu t di truyn vn ng prokaryote a. Trnh t on xenTrnh t on xen (insertion sequence) l mt on ADN ca vi khun di chuyn t mt v tr trn nhim sc th n v tr mi trn cng nhim sc th hoc trn nhim sc th khc. Yu t IS khi xen vo gia gen c th lm gin on trnh t m ha v lm bt hot s biu hin ca gene.

-V d: Yu t IS khi c tn hiu kt thc phin m v dch m s lm cn tr s biu hin sau promotor trong cng operon.46 Mt vi trnh t v kch thc ca on xen:Trnh t xen voS bn sao xen vo trong E.coliChiu di (bp)on lp li o ngc (bp)IS15 - 8 bn sao trn nhim sc th76818 - 23IS25 bn sao trn NST1 bn sao trn plasmid132732 - 41IS3140032 - 38IS41 - 2 bn sao trn nhim sc th140016 - 18IS5Cha bit1250Ngn5 bn sao trn NST2 bn sao trn plasmid Tt c cc yu t IS u cha on ADN m ha cho protein, c gi l transposase, l enzyme cn thit cho s di chuyn ca yu t IS t mt v tr trn nhim sc th n v tr khc. on gen ny nm gia 2 on lp li o ngc (inverted repeat - IR) ngn. V d: S ti t hp ca plasmid v nhim sc th ca E.coli to ra nhng chng Hfr qua trao i cho n gia yu t IS trn plasmid v yu t IS trn nhim sc th.- Hfg l t bo c kh nng vn chuyn gen vi tn s cao, mang nhn t F c s lng ghp vo NST ca vi khun. (nhn t sinh sn F l mt plasmid)48b. Gene nhy ca prokaryoteCc yu t IS ring l khng ch c kh nng t di chuyn m khi hai yu t ny nm gn nhau th chng c th vn ng nh mt n v hon chnh v mang theo cc gene nm gia chng. Cu trc phc tp ny c gi l transposon. C hai kiu transposon vi khun:+ Transposon hn hp (composite transposon)+ Transsposon n gin (simple transposon)

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Hnh 1. c trng v cu trc ca transposon hn hp (composite transposon) v transsposon n gin (simple transposon)

- Transposon hn hp cha nhiu gene nm gia 2 trnh t IS gn nhau, c hng ngc nhau to ra tnh t lp li o ngc (inverted repeat - IR). Mt trong 2 yu t IS m ha cho transposase xc tc cho s chuyn v ca c transposon. Chng hn Tn10 l transposon hn hp mang gene m ha cho tnh khng khng sinh tetracyline. Gene ny nm gia hai yu t IS10 c hng ngc nhau.- Transposon n gin gia cc trnh t IR, nhng nhng trnh t ny ngn ( ADN v xen vo v tr mi (enzym transcriptase).(Yu t sao chp ngc: tng t slide 24)53- Cc IS c th vn chuyn gen bt k khc.

IS tn TN10 (mu hng) vn chuyn plasmid vo NST to ra 2 transpoinson. Transpoinson mi c to thnh c IS b thay i hng. 54- Transposon c th chuyn v sao chp.

- Sao chp transpoinson donor (th cho) sang recipient (th nhn).(thuc yu t sao chp: sao chp v xen vo v tr mi (enzym transposase).)55- Chuyn v bo tn.

- Transpoinson th cho c chuyn trc tip sang cho th nhn. Ko xy ra s sao chp transpoinson. (phng thc chuyn v kiu ct - dn)56d. Yu t TnA

- TnA l cc yu t vn ng phc t c cc gen m ha cho kh nng vn ng ca chng v mang cc gen chn lc.- C kch thc ln (khong 5kb) v phc tp hn cc yu t Transposon hn hp.

57 Cu trc TnA (Tn3: 4957 bp).

+ H TnA c on trnh t lp li hai u 38 40 bp),v tr res gia v ba gen.+ Res (resolution site): v tr ti t hp c hiu.+ TnpA: transposase.+ TnpR: resolvase (cht c ch).

+ ampR (hay bla) m ha + -galactamase (xc nh tnh khng vi amp.58- C ch chuyn v ca Tn3

Cng ko hiu cho lm. Ch yu da v my ch nh nh ni hnh :D

593.2. Yu t di truyn vn ng eukaryote Cc yu t di truyn vn ng eukaryote chia lm 2 nhm l cc retrotransposon v cc DNA transposon.a. Cc retrotransposon Gery Fink v cs. l nhng ngi u tin s dng nm men nghin cu iu ho hot tnh gene eukaryote. Cc tc gi ny phn lp c hng ngn t bin gene HIS4 m ha enzyme tham gia tng hp histidine. Trong s hn 1.500 t bin ngu nhin HIS4 c tm thy c 2 t bin c kiu hnh khng bn vng. Cc t bin khng bn vng ny c tn s phc hi li dng kiu di cao 1.000 ln hn cc t bin HIS4 khc. Nhng t bin ny cho on DNA ln xen vo gene HIS4, s xen vo ny c thc hin do mt trong cc yu t l Ty ca nm men. C 35 bn sao ca yu t xen on gi l Ty1 genome ca nm men.

60Vic to dng nhng yu t ny t cc allele t bin cho thy xen on ny khng ging vi yu t IS hoc transposon ca vi khun. Thay vo chng c c tnh ca retrovirus (virus ca ng vt). C s ging nhau trong cu trc v thnh phn gen ca retrovirus v yu t Ty1 c phn lp t t bin HIS4.61 Ging vi retrovirus, transposon ca nm men c lp on cui di (long terminal repeat sequence) LTRs, cha hng trm cp base, c gi l trnh t nm 2 pha on m ha, c hai u cha gen gag v gen pol.

Retrovirus c t nht 3 gene m ha cho 3 protein trong qu trnh sao chp: gen gag m ha cho mt protein c vai tr lm bin tnh RNA genome. Gen pol m ha enzyme reverse transcriptase. Gene env m ha cho protein v. Yu t Ty ch cha gen gag v gen pol, khng cha gene env.Vo nm 1985, J.Bocke v G. Fink chng minh, yu t Ty1, ging vi retrovirus, thc hin vic di chuyn qua trung gian RNA. Chng bt u bng bin i yu t Ty1 ca nm men c to dng trn plasmid. Trc tin mt u mt ca yu t, c s xen vo mt promotor c hot ha nh thm galactose vo mi trng. Th hai, mt intron t mt gene khc ca nm men c a vo vng m ha ca transposon Ty. S thm vo galactose lm tng tn s chuyn v ca yu t Ty bi bin i. iu ny lm tng s lng RNA, v galactose kch thch phin m RNA Ty bt u t promotor nhy cm galactose.

62- S chuyn v nh retrotransposition

- Yu t Ty1( phin bn t retrotransposon ) c phin m mARN i ra t bo cht nh enzim phin m ngc to nn ADN bn sao ca yu t Ty1 Ty1 chui vo nhn chn vo NST khc.63b. ADN transposon Nhiu yu t di ng c tm thy eukaryote chuyn v bng c ch ging vi vi khun. Bn thn yu t IS v transposon hoc l bn sao ca chng c th xen vo v tr mi trn genome. Cc yu t di chuyn theo cch ny c gi l yu t nhm 2 hoc ADN transposon. Yu t di ng c McClintok pht hin u tin ng l cc ADN transposon. Tuy nhin tnh c trng phn t ca ADN transposon u tin li l yu t P rui dm.64a. Yu t P P di khong 2907 bp, cha on lp ngc chiu hai u di 31 bp. - P c 4 exon.- C th chng P c khong 30 50 yu t P.

- Yu t P c 4 on m ha.65Hin tng lon sn con lai rui gim:- P X M =>Con lai lon sn.- Chng P mang yu t di truyn khi xm nhp vo t bo trng chng M gy lon sn.

c P lai Ci M con lai biu hin bnh thng nhng ko sinh sn c ko c con chu.c M lai ci P con lai biu hin bnh thng, sinh sn bnh thng.66

- Trong cc m soma, hai intron u b ct b s sn sinh ra protein c ch (66 kD) hot tnh ca yu t P.- Trong cc m t bo mm, c intron 3 cng b ct b, sinh ra protein 87 kD, l enzym transposase.Gii thch c ch gy lon sn rui dm67

- S hot ng ca yu t P ph thuc vo cytotype trng thi yu t ny truyn theo dng m qua t bo cht ca trng.Con c mang yu t P to protein 87 kD, l enzym transposase. Con ci ko c cytotype (loi t bo) ko quy nh di truyn theo dng m qua t bo cht ca trng. yu t P xm nhp vo t bo trng con lai lon sn.(Gii thch c ch gy lon sn rui dm)68

Con c M lai con ci mang yu t P. con ci c cytotype trong m soma, hai intron u b ct b s sn sinh ra protein c ch (66 kD) hot tnh ca yu t P con lai biu hin bnh thng. Ko b lon sn.(Gii thch c ch gy lon sn rui dm)69b. Yu t Ac v Ds ng, yu t Ac v Ds c th di chuyn trn nhim sc th, tc ng ln cc gen kim tra mu sc ca cc ht aleuron. Cc yu t ny c phn lp cho thy c lin quan vi ADN transposon ca vi khun v ca cc eukaryote khc. Ging vi yu t P ca rui dm, yu t Ac c on cui lp li o ngc m ha cho transposase, yu t Ds li khng m ha cho transposase. Khi Ac c trong b gen, transposase ca n c th bm vo u mt ca c yu t Ac v Ds v khi ng s chuyn v ca chng.Yu t Ac v Ds thuc h transposon n gin. Ngoi ra, cn c cc h yu t di ng khc ng. Mi h cha yu t t ng m ha cho transposase c th chuyn c yu t trong cng mt h, nhng khng th chuyn n cc h khc v transposase ch c th bm vo u mt ca cc thnh vin trong h.

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- Cc h gen nhy ng:Pha tri (Ac, Mp, Spm, En, Dotted, MuDR) l cc h gen nhy c kh nng t vn ng. Pha phi (Ds, dSpm, I, Unnamed, Mu) l cc h gen nhy khng c kh nng t vn ng.

71- C ch gy t gy Ds:

- t gy Ds lm mt i mt on NST khng tm. Nu on NST mang gen tri th s mt on dn n bin i kiu hnh.V d: Ds gy t gy on on khng cha tm ng, mang cc gen Cl, Bz, Wx (gen tri) qua qu trnh nguyn phn biu hin kiu hnh bin i.72 4. Yu t di truyn vn ng ngi

- Ngi c khong 3000 5000 L1 hon chnh v khong 500 000 L1 khng hon chnh (b ct xn u 5. Ch c mt s t L1 hon chnh c kh nng vn ng.- Ch c Alu c kh nng chuyn v.

73 ngi, yu t di ng chim mt na genome ngi. a s yu t di ng thuc 2 dng retrotransposon l yu t nhn ri rc kch thc di (long interspersed nuclear element) LINEs v yu t nhn ri rc kch thc ngn (short interspersed nuclear element) SINEs.

- LINE di chuyn nh retrotransposition s dng yu t m ha reverse transcriptase, nhng li thiu mt vi tnh cht v cu trc ca yu t ging retrovirus bao gm LTR.- SINE c m t nh l LINE khng t ng, v chng c tnh cht cu trc c trng ca LINE nhng khng m ha cho reverse transcriptase ring. Ngi ta cho rng chng di chuyn c nh enzyme everse transcriptase c m ha bi LINE trong genome.

74- SINE ngi c gi l trnh t Alu v n cha trnh t im ct ca enzyme ct hn ch Alu. Genome ca ngi cha hn 1 triu trnh t Alu ch mt phn hoc ton b, chim hn 10% genome ca ngi. Trnh t Alu y c kch thc 200 nucleotide. ADN genome mang yu t di ng ln hn 20 ln ADN m ha cho tt c protein ngi.Tn s t bin ngu nhin do xen vo yu t nhm 2 l thp cha n 0,2% trong tng cc t bin ngu nhin. Trong khi nhng t bo ng vt khc nh chut do xen retrotransposon ln n 10% t bin ngu nhin, cao hn 50 ln ngi c l lin quan vi hot tnh ca yu t retrotransposon cao hn chut.

75VI. TM NG V CU TRC TM NG- Cu trc centromere hon chnh l 1 phc hp rt phc tp vi s tham gia ca nhiu loi protein ng vai tr khc nhau bao gm: ADN li chromosome lin kt inner Kinetochore v phc hp protein kinetochore.- Centromere l mt vng AND thng tm thy gn gia mt NST, ni 2 chromatid tip xc. N tham gia vo s phn chia ca t bo, l im gn t v sc.1/ V tr centromere trn NST:

- Centromere chia th nhim sc thnh 2 vai, chiu di ca 2 vai ph thuc vo v tr centromere v phn loi cc th nhim sc.- T ta c th phn loi NST theo v tr ca tm ng thnh: NST tm mt, NST tm lch, NST tm gia v NST tm cn gia.Ic=P/(P+Q) P:chiu di vai ngn Q:chiu di vai di

A: Th nhim sc tm mt (acrocentric chromosome) c trung tit u mt ca vai ngn.B: Th nhim sc cn mt (telocentric chromosome) c trung tit gn u mt ca vai ngn.C: Th nhim sc cn tm (tm lch) (submetacentric chromosome) c trung tit gn chnh gia (vai P ngn hn vai Q).D: Th nhim sc tm gia (metacentric chromosome) c trung tit chnh gia chia 2 vai bng nhau.a/ Cu trc v trnh t AND-CDE:- Trong qu trnh ny chi ca nm men (Saccharomyces cerevisiae), chiu di on AND centromere (CEN AND) cn thit phn bo l 125bp v c th c chia lm 3 vng trnh t bo tn CDEI, CDEII, CDEIII.2/ Cu trc centromere:- CDE-centromere AND Element- l nhng nhn t c vng trnh t AND xc nh ca centromere mang vng trnh t bo tn v trnh t tng ng. C 3 nhn t chnh l CDEI, CDEII v CDEIII.

- Mt nghin cu ca Hieter v cc cng s cho thy s chn lc chc nng ca CEN AND da vo cc plasmid ARS mang 1 gen SUP11 tARN. - Cc plasmid ARS trong nm men S.Cerevisiae c kh nng t ti to, nhng trong qu trnh phn chia ca t bo, cc plasmid ARS rt him khi c truyn cho cc t bo con, do chng c tch ly t bo m. - CEN ADN c trong plasmid s gip cho chng c phn ly ng cch. Nhiu bn sao ca gen SUP11 tARN s cht v ch c plasmid c CEN ADN sng st.- V tr trung tm ca tt c cc CEN ANDs l vng giu AT, nht l trnh t ca nhn t CDEII (87-98% A:T v T:A). Vng trnh t ADN giu AT thng c xu hng thay i v tr sp xp ca trnh t A:T v T:A, nhng cc nhn t ny khng mang trnh t nhn bit trnh t bo tn.- Nh vy, vic thay th 1 phn trnh t CDEII mt cch ngu nhin trong vng trnh t giu AT lm gim ng k chc nng ca centromere trong nguyn phn v gim phn.- CDEI v CDEIII nm lin k 2 u ca CDEII, l vng c mc bo tn cao v mang cc trnh t hai chiu. CDEI gm c vng trnh t c bo tn cao c chiu di l 8bp c mt c 16 CEN ADNs- Trong s tng phn, nhn t CDEIII di 16bp cho thy 1 phn tng ng gia 16 CEN AND, tr vng trung tm c bo tn cao. Phn cn li ca vng trnh t ny l 1 u giu A:T u 5 v 1 u giu T:A u 3.

b/ Cu trc cc protein:- ADN chromosome lin kt inner kinetochore: cha trnh t bo tn giu trnh t bo tn giu A-T c kch thc khong 220bp, 15-20nm. c chia thnh 3 vng.Vng IIIIIITrnh t 5A(G)TCACA (G)TG3>90% A-T25bpc bo tn caoChc nngPhn li NST v cc cc TB trong NP v GP1ng vai tr quan trng trong chc nng centromereng vai tr quan trng trong xc nh cu trc ADN

- Inner kinetochore l phc hp protein trong c 2 loi c ch nhiu:+ CENP-A (centromere proteins): dng bin th protein H3 thay th cho H3 ca nucleosomes, CENP-A l c s cho centromere hot ng. Vi t bo thiu CENP-A s phn chia xy ra khng cn chnh xc.+ CENP-B l loi protein lin kt vi trnh t lp li trn ADN ca tm ng. ngi, vng lp li ny c bit n l alpha satellite ADN.- Hot ng kinetochore protein t di s kim sot ca h thng t bo bi nhng phc hp c chc nng iu ha: APC, phc hp thc y k sau (anaphase-promoting); CEN, ADN tm ng; SCF, phc hp ubiquitin-ligase.+ Ngoi ra cn c s tham gia ca nhiu loi CENP khc. Ngy nay ngi ta bit c 20 loi CENP khc v c th tng hn na trong thi gian ti khi chng ta hiu r s hnh thnh kinetochore.