CHNG 2CU TRC CA GEN, T CHC CC GEN GENOM V IU HA S BIU HIN CA GEN

M DI TRUYNQa trnh truyn t thng tin di truyn sinh vt c din ra nh sau: ADN ARNm Protein (Tnh trng). Ngi M truyn t thng tin cho nhau bng ting Anh My tnh truyn t thng tin cho nhau bng m nh phn: 1, 10, 11, 100, 101 Sinh vt truyn t thng tin bng m di truyn.

nh ngha: M di truyn l trnh t cc nucleotit trn phn t DNA. Trong mt n v m l mt nhm gm ba nucleotit lin tip (cn gi l codon hay b ba m ho). Mi codon m ho tng ng cho mt phn t axit amin trn Protein. Trnh t sp xp cc codon tren DNA quy nh trnh t sp xp cc axit amin trn phn t Protein. C 20 loi axit amin trong c th sinh vt. C 4 loi nucleotit, ghp m b ba nn s c 64 b ba m ho, m ho cho 20 loi axit amin sinh vt. Do s lng b ba m ho nhiu hn s lng aamin nn c nhiu b ba cng m ho cho mt aamin, iu ngc li khng ng.

Gii m cc codonADN truyn thng tin ca n qua bn sao mARN, ngi ta to ra nhng mch mARN c thnh phn nucleotit khc nhau lm khun tng hp cc chui polypeptit (chui axit amin) trong mi trng in vitro. Phn tch s tng ng gia th t b ba trn mARN vi th t axit amin trong chui polypeptit, chng ta c th bit c b ba no quy nh loi axit amin no, tc l chng ta gii m cho cc codon.

Cc b ba m ha (cc codon)V tr th nht (u 5) U UPhe Phe Leu

V tr th 2 CSer Ser Ser

V tr th 3 (u 3) GCys Cys Stop U C A

ATyr Tyr Stop

Leu

SerPro Pro Pro Pro Thr Thr Thr Thr Ala Ala Ala Ala

StopHis His Gln Gln Asn Asn Lys Lys Asp Asp Glu Glu

TrpArg Arg Arg Arg Ser Ser Arg Arg Gly Gly Gly Gly

GU C A G U C A G U C A G

C

Leu Leu Leu Leu Ile Ile Ile Met

A

G

Val Val Val Val

Mt s b ba c bit trn mARN- B ba AUG (m ho melthianin) l b ba duy nht ng vai tr l tn hiu bt u cho qu trnh tng hp ca mt chui polypeptit (b ba khi u). - C ba b ba l UAA, UGA, UAG khng m ho aamin no m l tn hiu cho s kt thc (Stop) qu trnh dch m - truyn t thng tin di truyn t mARN n Protein.

Tnh cht ca m di truyn1. S c m theo cc b ba lun l lin tc v khng c tnh chng cho. iu c ngha rng, khi im khi u ca s c b lch i, hoc khi thm, mt nhng nucleotit (s lng khc ba), th khung m b lch i so vi trnh t ban u 2. M di truyn c tnh cht d tha: 61 b ba/20Aamin. Nhng b ba cng m ha cho mt axit amin no gi l cc b ba ng ngha. Cc axit amin nh lxin, serin, acginin c ti 6 b ba ng ngha. Cc b ba ng ngha hu nh ch khc nhau baz th ba. V d:GGU, GGC, GGA, GGG u m ha cho glixin 3. M di truyn c tnh cht vn nng ngha ca m di truyn l ng mi sinh vt.

THC HIN THNG TIN DI TRUYN Qa trnh sao m (transcription) Qu trnh dch m

QA TRNH SAO Mnh ngha: Sao m l qu trnh truyn t thng tin t chui xon kp DNA ti mch n ARN. Trong , mt trong hai mch ca chui DNA c lm khun tng hp ARN gi l mch c ngha hay l mch mang m gc

C ch sao m sinh vt nhn sThnh phn tham gia 1. on ADN cn sao m (on gen) Vng khi u, vng mang m, on kt thc 2. Enzym ARN-polymerase Enzyme ny c cu trc t 4 tiu phn: +2 tiu phn nh ging nhau k hiu l , +2 tiu phn ln khc nhau , 1. Nhn t sigma (). n gip cho ARN-polymerase nhn bit c im khi u trn ADN. 3. Cc nucleotit dng triphophat (ATP, GTP, UTP, CTP)

Giai on 1: Nhn bit vng khi uVng khi u gm 2 thnh phn chnh: on khi u l mt on gm 6 nucleotit c trt t 5TATAAT-3 nm cch im bt u phin m 10 cp nucleotit. im nhn bit (recognition sequence) nm cch im khi u phin m khong 35 nucleotit v pha trc c trnh t 5 TTGACA3

ARN-polymerase nh v vo DNA da vo 2 im m c th trn on khi u

ARN-polymerase nhn bit v bm v hai on c th nm gn cc v tr -35 v -10 trc im bt u sao m

Giai on 2: Giai on ko di chuiARN-polymerase trt dc theo gen v xc tc s bin tnh cc b ca hai si DNA lm l ra si khun 3 5 c th khi u qu trnh tng hp mARN. Di tc ng ca ARN-polymerase, DNA c tho xon, cc nucleotit trong mi trng tin vo ghp b sung vi cc nucleotit trn si khun 3-5. Ti vng c phin m ADN xon li nh ban u.

C ch sao m sinh vt nhn s (prokaryote)

Giai on 3: Kt thc Khi ARN polymerase chy ht on mang m ri chy qua on kt thc giu GC v AT, phn t enzym ny dng li.

Do tc ng ca nhn t Rho () (nhn t gii phng), si ARN v enzyme ARN-polymerase c gii phng khi ADN khun.

c im sao m Prokaryote vi khun ch c mt loi ARN-polymerase, tng hp cho c 3 loi phn t ARN: ARN thng tin (mARN), ARN ribosome (rARN) v ARN vn chuyn (tARN). Trn mt on khun ADN s sao m c th din ra lin tc trn mt on DNA vi s tham gia ca nhiu phn t ARN-polymerase.

C CH SAO M SINH VT NHN CHUNTHNH PHN: 1. Gen cn sao m. + on khi ng (Promoter). + on mang m di truyn + on kt thc (Termination)

2. ENZYM C 3 loi ARN-polymerase trong nhn t bo sinh vt nhn chun (I, II v III) ARN-polymerase I. Enzyme ny chuyn trch vic sao m cc gen tng hp cc phn t rARN 28S, 5,8S, 18S. ARN-polymerase II. Cn thit cho vic tng hp phn ln cc loi ARN khc, c bit l ARNm. ARN-polymerase III. C chc nng phin m cc tARN v rARN 5S. 3. Cc nhn t sao m: c t nht 6 nhn t sao m hot ng h tr ARN polymerase thc hin qu trnh sao m v c k hiu l TFIIA, TFIIB, TFIID, TFIIE, TFIIF, TFIIH.

1. Gen cn sao m 1-1 on khi u 3 ca on ADN thng c 3 on trnh t c hiu gm:

1-1.Hp TATA : l mt on gm 7 nucleotit cng c trnh t 4 nu u tin l TATA, nm trc im bt u sao m khong 25 30 nucleotit, c tc dng h tr cho ARNpolymerase nhn bit ng v tr khi u sao m (initiator).1-2.Hp GC c trnh t kiu GGGCGG. 1-3.Hp CAAT c trnh t kiu CCAAT. (2 hp sau nm trc im khi ng phin m khong t 40-100 nucleotit c vai tr trong iu ho sao m).

1-2 on mang m (bt u bng mt im gi l im bt u sao m 1-3 on kt thc (terminator) Cc on kt thc sinh vt nhn chun chng ta mi bit rt t . Hu ht cc gen m ha protein th phn ng sao m c dng li sau khi ARN-polymerase II vt qua v tr c bit AATAAA trn DNA (gi l v tr polyA).

Giai on Bt u sao m Nhn t TFIID gn vi hp TATA ca on gen cn sao m thng qua mt tiu phn b sung ca n l TBP (protein gn trc tip vo ADN) TFIID l mt nhn t v tr, n c nhim v hng RNA polymerase ti promoter ca gen cn sao m. TFIIA gn vi TBP v TFIID v lm n nh TFIID. TFIIB gn vi TBP v TFIIF v RNA polymerase. TFIIF l mt nhn t c vn ng tch mch v vy c th n lin quan n qu trnh m si DNA, lm xut hin mch n thng ti im Promoter. Cc TF cn li c nh vo hon thin b khi ng cho ARN polymerase.

Giai on Sao m + Kt thc ARN polymerase II m si kp, tng hp mt mch n mi theo chiu 5 3 trong sut qu trnh n chy dc theo mch n c m v dng li sau khi chy qua on poly A kt thc. sinh nht nhn chun, on ARN c to ra t ARN poplymerase II ch l mARN s cp, mARN s cp ny sau c to m (methyl ho ti u methionyl) v gn thm ui poly A ri tri qua qu trnh thnh thc ho trc khi tham gia vo qu trnh dch m. Video Clip

DCH M nh ngha: Dch m l qu trnh tng hp mch polypeptit riboxome, trn c s khun mu ca ARNm. Trnh t c cc b ba m ha trn ARNm quyt nh trt t cc loi axit amin trong mch polypeptit. Tham gia vo qu trnh dch m bao gm: mARN Ribosome tARN Aminoaxyl-ARN-synthetase Axit amin c hot ho. Mt lot cc yu t protein khc

Ribosome - L ni xy ra qu trnh tng hpmch polypeptit. - L mt phn t gm 2 tiu phn + Tiu phn nh 30S + Tiu phn ln 50S. - Mi tiu phn u c hnh thnh t rARN v protein. - ln v thnh phn cu trc ca ribosome bin ng ln cc i tng sinh vt khc nhau.

Hnh 2.6. M hnh ribosome

tARN L cc phn t ARN c sao m t on gen c th (gen tARN) tARN c nhim v xp cc axit amin vo ng v tr theo trnh t m di truyn trn mARN Sau khi c to ra bng qu trnh sao m, mt v tr xc nh ca n xy ra bin i mt s gc (hydrouraxin (DHU) v pseudouridin). tARN sau un li to cu trc khng gian c dng hnh c ba l nh cc lin kt hydro.

- u 3 ca tARN lin ktvi axit amin. Lun c trnh t CCA

- mt nh un c cha mt b ba m ho (anticodon) ng vi axit amin m tARN mang. Do cc axit amin c mang chnh xc n v tr trong chui polypeptit ng vi th t m ho trn mARN. Hnh 2.7. S cu trc ca tARN

I vng tht DHU; II anticodon; III on thm IV vng tht TC

S cu trc ARNt

Hot ha axit amin. Mi loi axit amin c mt trong t bo cht c nh vo tng ARNt thch hp nh hot ng xc tc ca enzyme aminoaxyl-tARN synthetase c th. Enzyme ny xc tc cho phn ng ATP hot ha axit amin to nn phc hp aminoaxyl-AMP lin kt vi enzyme E + ATP + A.amin E[Aamin~AMP] Sau phc hp ny kt hp vi ARNt bng lin kt ng ha tr to nn aminoaxyl-ARNt E[Aamin~AMP] + ARNt Aamin~ARNt + AMP + E Ton b qu trnh trn gi l qu trnh hot ha axit amin.

Giai on 1: Tiu n v ribosome b bm vo ARNm ti v tr ca codon khi u AUG.

ARNt axit amin m u, mt u mang b ba i m (AUG), mt u mang axit amin m u Methionyl tin vo ribosome v khp anticodon ca n vi codon khi u theo nguyn l b sung. Tip tiu n v ln ca ribosome bm vo tiu n v b to ra mt ribosome hot ng hon chnh. Lc ny Met-tRNA v tr P v bn cnh v tr A cn trng Mt ARNt th hai i vo v tr A v khp vi codon th 2 Gia hai axit amin hnh thnh lin kt peptit, phn ng c xc tc bi enzyme peptidyltranspherase, kt qu l to ra mt peptidyl ARNt v tr A.

Giai on 2: Ribosome dch chuyn sang mt codon mi dc ARNm theo chiu 5 3. Dch chuyn ny y ARNt-1 v tr P ra khi ribosome, v a ARNt-2 vo v tr P lm v tr A b b trng. Aminoacyl - ARNt th 3 i vo v khp aticodon ca n vi codon v tr A, lin kt peptit th hai c hnh thnh.

Ribosome li dch chuyn sang codon k tip C nh vy, li xy ra qu trnh tng t dc theo sut chiu di ARNm cho n codon c hiu kt thc trn ARNm.

Giai on 3 Ribosome dch chuyn ti khi v tr codon ti A l codon kt thc (UAA, UAG, UGA). Mt protein c bit gi l nhn t gii phng (RF) s tin vo A v khp vi b ba i m.

S c mt ca RF cng vi enzyme peptidyl transferase gy ra s chuyn dch ca ribosome v tch chui polypeptide ra khi ARNt cui cng, Hai tiu n v ca ribosome cng tch ra dng t do. Chui peptit c gii phng.

Polysome Sau khi c khong 25 axit amin c lin kt vo chui polypeptide-1, ribosome th nht tch xa codon khi u, codon ny li lin kt vi ribosome th 2. V s chuyn dch xy ra song song. C nh vy n ribosome th 3th n. Nh vy, trn 1 ARNm c nhiu ribosome lm vic to nn mt n v dch m polyribosome hay polysome

S sao chp ARN din ra ng thi nhiu ARN-polymerase

S thc hin thng tin di truyn t bo

GEN L G? KHI NIM TNG QU V H THNG GEN T BO

Gen l g? Gen c vai tr g trong c th sinh vt? Gen c cu to v hot ng nh th no?

Khi nim v gen ca MorganCc gen nm trn nhim sc th v l cc n v khng chia nh c na Cc n v ny l: n v t bin, ngha l khi xy ra t bin trong gen, gen s b bin i hon ton sang mt trng thi mi. n v ti t hp, ngha l trao i cho khng bao gi din ra bn trong gen, ch c th din ra gia cc gen. n v chc nng: mt gen quy nh mt loi chc nng trong c th sng.

Theo Morgan, xc nh hai t bin nghin cu c nm trong cng mt gen hay khng (c alen vi nhau khng) c th cn c vo 2 tiu chun: Tiu chun ti t hp: Nu cc t bin khng ti t hp vi nhau (gia chng khng xy ra trao i cho) th chng alen vi nhau. Nu khng, chng thuc v hai gen khc nhau. Tiu chun chc nng: khi lai hai th t bin vi nhau nu cho th h lai c kiu hnh t bin, th hai t bin thuc v cng mt gen (chng alen vi nhau), cn nu cho th h lai c kiu hnh di (bnh thng) th cc t bin thuc v hai gen khc nhau.

a1

A2 x x x A2 a1 x x A1

A1

a2

a1 x x x a1

a2 x x a2

xx a1

xx A1 A2 x x a2

xx a2

x a1 x a2

Kiu hnh di Hai t bin a1 v a2 khng alen thuc v 2 gen khc locus

Kiu hnh t bin Hai t bin a1 v a2 l 2 alen thuc v cng 1 locus

Chc nghim chc nng cho hin tng tng ng

kin ca bn v quan im ca Morgan?ng ? Khng ng ? Ngy nay chng ta c th khng nh: Gen l mt on nm trn phn t DNA, ng vai tr l mt n v cu trc ca thng tin di truyn v m nhn mt n v v mt chc nng.

Th nghim chng minh gen khng phi l n v ti t hpC.Oliver, M.Green v E.Lewis (1951) th nghim trn i tng rui gim vi s lng c th rt ln pht hin thy cc t bin c cho l nm trong cng mt gen theo tiu chun chc nng th li ti t hp vi nhau. Trao i cho gia cc t bin trong mt gen vn din ra bnh thng

Cc loi gen trong c th sinh vtHin ti, phn t DNA ca sinh vt (khng bao gm DNA trong ty th v lc lp c chia ra cc vng chc nng gi l cc gen, bao gm 6 loi chnh: 1. Cc gen cu trc: tng hp cc protein cu trc v cc protein enzyme, gii hn bi b ba khi u v b ba kt thc. 2. Cc gen tARN mang thng tin tng hp nn cc ARNt. 3. Cc gen rARN mang thng tin tng hp ARNr. 4. Cc vng iu ha c hiu nm cnh cc gen cu trc, l cc promotor, operator . 5. Cc vng m (spacer) tch bit gia cc gen 6. Cc vng m ha cc tn hiu khi u v kt thc dch m v mt s vng thc hin hng lot cc chc nng khc th hin cha hon ton sng t.

ADN TRONG TY TH, LP THADN TY TH (mt ADN) M ha cho 20 30 loi ARNt v 10 12 loi protein trong thnh phn bn trong ti th. Dng chui kp, trn mch, vng ADN LP TH (cp ADN) C hm lng GC khc bit vi ADN trong nhn v ADN ti th. mt s loi thc vt bc cao c ti 6000 phn t cpADN trong t bo, phn b trong khong 40 80 lp th. M ha nhiu protein cu to lp th v cc enzym cn cho qu trnh quan hp. Ngoi ra cn c c mt s protein ca ribosome.

2.2 CU TRC V IU HA HOT NG CA GEN SINH VT NHN S2.2.1 Khi nim chung gen hot ng theo c ch iu ha Biu hin ca gen chu s kim sot ca cc c ch iu ha, chng xy ra theo chng trnh nh trc v p li l nhng tc ng ca s bin i mi trng v trong t bo.

sinh vt nhn s, mc ch ca s iu ho biu hin gen lnhm iu chnh h enzyme cho ph hp vi cc tc nhn dinh dng v l ho ca mi trng, m bo 2 yu cu chnh ca

t bo: tng trng v sinh sn. S iu ho biu hin ca gen ch yu c tin hnh giai on phin m.

M HNH OPERON sinh vt nhn s, cc gen thng hp li thnh cm hng tithc hin mt chc nng nht nh gi l operon. C ch iu ha ch yu c thc hin thng qua cc operon. 1961, F. Jacob v J. Monod a ra m hnh operon: + on ADN m ho (cc gen cu trc) quy nh tng hp protin.

+ on ADN tham gia vo qu trnh iu ho hot ng ca cc gencu trc. + O- operator: vng iu hnh :21 i baz

+ P- promotor: vng khi ng: 85 i bazKt lun: operon l mt h thng hot ng bao gm cc gen cu trc nm di s kim sot ca b phn iu ho lin kt st

chng.

2.2.2 Lac operon vi khun, iu ha m tnh Cc enzyme tham gia vo phn gii ng lactose E.coli: -galactoside tham gia vo s phn gii lactose thnh galactose v glucose; -galactoside permease cn cho s thm nhp ca galactose vo t bo;

-galactoside transacetylase chuyn nhm acetyl t acetyl-CoAvo -galactoside. Khi nui cy khun E.coli trong mi trng c lactose th thy hot tnh ca cc enzyme trn tng mnh. Nh vy lactose cm ng s hot ng ca cc gen kim tra cc enzym trn.

Cu trc ca m hnh lac operonPhn 1: Cc gen cu trc kim tra tng hp cc enzym: - Gen kim tra tng hp -galactoside (k hiu l Z), c di 3.510 i baz. - Gen kim tra tng hp -galactoside permease, k hiu l

Y, c di 780 i baz.- Gen kim tra tng hp -galactoside transacetylase, k hiu l A, c di l 825 i baz. Khi sao m, cc gen cu trc c sao cng nhau trn mt ARNm, to thnh mt khi gi l ARNm a cistron.

Phn 2: Vng ADN lm nhim v iu ha s hot ng ca cc gen cu trc: - Vng O operator (vng iu hnh hay ch huy), c di 21

i baz- Vng P promoter (vng khi ng), c di chng 85 i baz. Vng P c chia lm 2 on: on A l ni tip nhn

s tc ng ca protein hot ha trao i cht CAP (CataboliteActivator Protein) v on dnh cho enzyme ARN-polymerase lin kt tin hnh sao m.

Gia hai phn cch nhau bi mt on c di khong 37i baz, gi l on dn u.

C ch iu ha m tnh S ng m cc gen cu trc ph thuc vo protein iu ha(protein c ch), do gen iu ha I kim tra. h lactose gen I nm ngay st t chc operon v c di 1.045 i baz vi vng khi ng (P) di khong 80 i baz. Gen I hot ng theo c ch t iu khin. Khi protein iu ha c tc ng bao vy vng O c ch sao m cc gen cu trc.

Khi trong mi trng c mt cht cm ng (inducer) (VD: nglactose, isopropylthiogalactoside (IPTG)), n tc ng vi protein iu ha protein iu ha bin i cu trc khng gian mt

hot tnh bao vy vng O vng O c gii ta. Nh , s hotng ca ARN- polymerase c din ra bt u t im khi ng. Kt qu l cc gen cu trc c sao m.

Lac Repressor molecule

S hot ng ca lac operon E.coli theo c ch iu ha cm ng m tnh

t bin gen lac lacI-

Kiu hnh t bin

Lac operon hot ng lin tc bi operator khng b bao vy Lac operon hot ng lin tc bi cht c ch khng bm c vo operator Lac operon ngng hot ng v ARN polymerase khng th bm c vo ADN Khng c cc sn phm glucose hay galactose c phn gii t lactose Lactose khng c vn chuyn vo trong t bo

O-

P-

lacZlacY-

Cc th t bin gen lac v biu hin kiu hnh ca chng

iu ha c ch m tnh (negative, repressive

control) operon sinh tng hp axit amin iu ho hot ng ca cc operon sinh tng hp axit amin cng din ra theo c ch iu ho m tnh. Nhng c s khc bit

so vi operon lac l: khi c tc ng ca sn phm axit amin(hnh thnh nhiu trong t bo) ln protein iu ho, lm cho n tr nn hot tnh bao vy vng O v c ch sao m.

Nh vy, axit amin c tc ng nh yu t ng c ch.

Khi t bo thiu aa, s sao m xy ra, hot tnh ca cc enzimtham gia vo sinh tng hp protin tng. Khi aa, cc gen cu trc ngng sao m. V d: Operon histiddin, Operon triptophan

M HNH OPERON TRYPTOPHAN

S v s iu ha hot ng ca Tryp operon theo c ch iu ha c ch m tnh (iu ha ngc retro-inhibition)

2.2.3 Mt s c ch iu ho khc.a) iu ha dng tnh (positive, inducible control)C ch iu ho:

Adenozinmonophotphat vng (cAMP) c tng hp trong

t bo vi khun nh enzym adenylxyclase.Khi vi khun sinh trng mi trng cha glucose, th nng ca cAMP t bo thp.

Khi mi trng cha ngun cacbon khc (lactose) thnng cAMP tng. cAMP kt hp vi mt protein hot ho trao i cht

(Catabolite Activator Protein CAP, protein ny c mho bi gen crp ) to thnh phc hp cAMP CAP. Phc hp ny lin kt vi vng A promotor gy hot ho

sao m cc gen cu trc.

S c ch iu ha dng tnh lac operon

Tc ng ca cAMP CAP khng ph thuc vo h gen iu ho I v operator, v th t bin gen crp v adenylxyclase khng sao m c ARNm ca operon lac, ngay c khi t bin lacI- hay Oc c mt. Nh vy, operon lac c th c iu ho mt cch c lp theo c ch dng tnh v m tnh. C ch iu ho dng tnh quan st thy cc operon

ca qu trnh trao i cht, nhng khng gp cc operonsinh tng hp.

b) C ch iu ho phc hp ara operonL c ch iu ho ca operon tham gia vo qu trnh chuyn ho ng arabinose vi khun, hot ng theo c ch iu ho phc hp, bao gm c s iu ho m tnh v dng tnh. C ch hot ng: Protein iu ho (c sao m t gen iu ho) c cu trc gm hai tiu phn. Protein iu ho lin kt vi hai vng iu hnh: + vng iu hnh ca operon

+ vng O2 gen iu ho T gy nn s bin dng on ADN ny, lm cho ARNpolymerase khng th lin kt vi im khi ng tin hnh sao

m cc gen cu trc.

Khi trong mi trng c mt ng arabinose, cht ny tcng vi protein iu ho lm cho n thay i cu trc khng gian dn n mt kh nng phong to vng iu hnh, tc lm mt s bin dng ca on ADN ny, to iu kin cho s hot ng ca ARN-polymerase. Song song vi hot ng trn, phc hp cAMP CAP lin kt vi ADN nh mt yu t iu ho dng tnh, nh s gn ARN-polymerase vo im khi ng c kch thch

mnh, thc hin qu trnh sao m ba gen A, B v D ara operon.

c. iu ho theo c ch sao m b d tryptophan Operon ny c on ADN t vng O ti gen cu trc 1 (140bp) - on dn ng, gm: + Mt trt t 26 baz khng tham gia m ho. + Mt trt t gm 45 baz ng vi 15 b ba m ho c 1 peptit ngn peptit dn ng (14aa: 2aa triptophan ng vi b ba 10,11). + Cc trt t cu trc dng un palindrome ging cu trc

vng kt thc ca 1 gen.

M HNH CU TRC ON ADN DN NG CA OPERON TRYPTOPHAN

C CH SAO M B Da) Khi trong t bo c Tryptophan Qu trnh sao m c tin hnh t on dn ng nh ARNpolymerase. Khi trong t bo c nhiu tryptophan, chng c ARNt a n lp rp theo hai codon 10 v 11 s trt ca ribosome din ra

bnh thng hon thnh tng hp chui peptid dn ng. Chuyn ng ca ARN-polymerase gp on attenuator gy tn hiu kt thc sao m on dn ng v s sao m b dng ti

.Nh vy, s sao m cc gen cu trc khng tip tc din ra khi trong t bo vn c tryptophan.

S iu ha theo c ch b d operon tryptophana) Khi trong t bo c axit amin tryptophan

b) Khi trong t bo thiu tryptophan: Khng c ARNt mang tryptophan ti ribosome tip tc tng hp chui peptid dn ng. Hu qu l ribosome b

dng li codon tryptophan. Phn dn ng ca ARNm cun li gy bin dng cu trc un c trng lm cho on attenuator khng thc hin c chc nng dng li. S trt ca enzyme ARN-polymerase c tip tc din

ra, dn ti s hon tt sao m cc gen cu trc ca operon.Nh vy, cc enzyme tham gia vo qu trnh sinh tng hp tryptophan c to ra, tryptophan c tch ly vi s

lng ln trong t bo.

b) Khi trong t bo khng c tryptophan

2.3. CU TRC V HOT NG CA GEN SINH VT NHN CHUN (EUKARYOTE)2.3.1. Cu trc exon intron ca gen 1977, nhm tc gi phng th nghim Cold Spring Harbor pht hin cu trc khng lin tc ca gen adenovirus 2: + di ca mch mARN tham gia vo dich m ngn hn so vi mch mARN sao ra theo khun ca chui ADN mun (L- ADN). + Bng phng php lai phn t : mARN to th lai khng tng ng trn ton mch L- ADN m ch xy ra 4 on: 1 on dn du ko di hn v 3 on ngn tip theo. Nhng on d ra ca LADN to nn nhng di un. Kt lun: hnh thnh mARN tham gia vo dch m, ch c th bng

con ng ct b cc on ARNm sao ra t gen. Cu trc ca gen gm nhng on tr khng mang m ha (intron), chng xen k vi cc on m ha (exon). Cu trc ny cn gi l cu trc khng lin tc hay cu trc khm ca gen.

nh vi in t v s cu trc gen - globin

Cu trc exon intron- S lng intron dao ng rt ln, c th t mt ti vi

chc .

- di ca cc intron v exon rt khc nhau.- di ca cc intron c bin ng rt ln. - Cc intron c tnh cht n nh v v tr cc gen gn ging nhau ca mt loi, hay gen cng loi ca cc loi khc nhau.

- Thnh phn cc nucleotit cc intron km n nh,bin ng nhiu trong tin ha. - Thnh phn ca cc exon n nh hn.

- a s cc gen, di ca intron chim t l ln hn nhiu so vi di ca exon. - Cc t bin xy ra trong vng intron thng xuyn hn, chng khng hoc t nh hng ti chc nng ca gen. - Vng gip ni gia exon v intron c c trng bng

cc trt t nucleotit (on gip ni): A(C)AG|GTA(G)AGT.on ny c vai tr quan trng trong s ct b cc intron v ni cc on exon li, v th n c tn gi l trt t tch ghp (trt t splicing). t bin xy ra vng gip ni c th dn ti s khng ct c cc intron, hay ct sai, do khng thu c ARNm thnh thc dch m.

2.3.2. Qu trnh thnh thc ha ARNm s cp

u 5 ca ARNm xy ra phn ng to m (capping), lphn ng methyl ha v tr s 7 ca guanozin v v tr s 2 ca ng ribose,kt qu l to ra m 7-

methylguanosinetriphosphate (m7Gppp). ui polyA c thm vo u 3 ca cc phn t ARNm, c vai tr y ARNm qua l mng nhn ra bo cht.

S tch ghp (splicing):

+ hai u ca mi intron (gn st im gip ni) u c hainucleotit n nh (5) GU..AC (3) (trt t chun). + Mt s ARN nh nhn (snARN) c cha hai dinucleotit b

sung vi cc trnh t chun intron. Cc snARN phi hp vienzyme tch ghp to thnh phc hp c hot tnh xc tc s tch ghp gi l ribonucleoprotein (snRNP) hay ribonucleaseP-snRNA. + C 5 loi snARN: U1, U2, U4, U5, U6 to thnh splicesome. + on intron un li hnh vng nh s tng tc ca n vi snARN theo trt t b sung. + Enzyme tch ghp thc hin vic ct b cc intron v ni cc exon.

S qu trnh thnh thc ha ARNm s cp (pre - ARNm)

Branch site A

Transesterification

A nucleotide with a 5- 3 phosphodiester and a 5- 2 phosphodiester linkage

Lariat structure

The chemical reaction that characterizes splicing is transesterification

Trans-splicing: When exons from two different original mRNAs are spliced togetherOnly apparent difference is the Y structure formed, rather than the lariatExamples - many trypanosome mRNAs; C. elegans messages to attach 5 leader; Chlamydomonas psa gene in chloroplast

Branch site

Splice site

Splice site

Branch site

Branch-point binding protein an RNA-free protein

E - complex

A - complexU4-U6 held together by base pairing of RNA componentsTri-snRNP particle U5 held in place by weaker protein-protein interactions

B - complex

U1 replaced by U6

Assembly of splicesome is complete

release

C complex (U2 contacts U6 to form active site) 2 transesterification reactions

Spliced mRNA

lariat

T tch ghp (self-splicing)L qu trnh tch ghp ARNm s cp xy ra do s xc tc

ca chnh phn t ARNm m khng c s tham gia ca ccprotein-enzyme khc. Phn t ARN c hot tnh xc tc gi l ribozyme.

Splicesomes may have evolved from Group II self-splicing introns

Splicesomemediated

Lariats released

Linear intron released

2.3.3. S tch ghp ny sinh, nhng ngha ca cu trc exon - introna. S tch ghp ny sinh

mt gen, qu trnh tch ghp ny sinh c th xy ra theonhiu cch, kt qu hnh thnh nhiu dng ARNm thnh thc khc nhau, gi l s tch ghp ny sinh.

i vi sinh vt nhn chun s tch ghp ny sinh khngnhiu. Tuy nhin n c ngha ln trong s to a dng cc sn phm v trong iu ho s biu hin ca gen.

SP

VH

C1

C2

C3

C4 C5

Cm 3

5T bo B

ARNm s cp ca chui nng

T bo plasma

SP VH

C1 C2 C3 C4 C5

AAAAA SP VH

AAAAA C1 C2 C3 C4 Cm

Chui nng IgM5

Chui nng IgMm

chui nh

chui nh

chui nh

chui nng

axit amin hydrophylic

axit amin hydrophybic

Hnh 2.19. S v s tch ghp ny sinh ARNm chui nng ca immunoglobin (IgM)

b) ngha ca cu trc exon - intron - To a dng cc sn phm v trong iu ho s biu hin ca gen. - Tnh cht cu trc khng lin tc, nhiu thnh phn ca gen c ngha trong tin ho hnh thnh nhng gen mi.

Nhiu gen phc tp c th xut hin thng qua s lp ghpkhc nhau t nhng on thnh phn

2.4. C IM CU TRC OPERON V IU HA GEN SINH VT NHN CHUN2.4.1. Nhng yu t iu ha ca operon v c im ca chng1. Promoter (vng khi ng) L ni ARN-polymerase gn vo tin hnh sao m ra cc ARNm. vng khi ng thng quan st thy nhng trt t c thnh phn baz nh kiu TATAAT.

Khi vng khi ng b bt hot ha (do t bin) th s saom b nh tr.

Vng khi ng ca cc gen do ARN-polymerase III sao m thng nm bn trong gen . V d, gen ARNt promotor cu to t hai khi phn cch nhau bi mt on khong 20 i baz, khi th nht cch im bt u sao m khong 8

30 i baz. Vng khi ng ca ARN-polymerase I nm pha trc gen ARNr, nhng cha hon ton xc nh c r v tr, hn na cc trt t ADN vng ny t mang tnh c trng v bin ng mnh cc loi.

2. Enhancer (vng tng cng sao m)

M.L. Brinstiel (1980) nghin cu cc gen histon t botrng ch v nhiu nghin cu sau ny thy: C nhng on ADN ngn nm nhng v tr khc nhau ca gen, c chc nng tip nhn thng tin lm tng qu trnh sao m - gi l vng tng cng sao m. c im: + Vng tng cng l yu t tc ng theo hng ng thi, chng ch c hot tnh khi nm trong khi thng nht cha gen m chng iu khin. + Vng tng cng khng c tnh hng, v tr ca chng c th thay i m khng nh hng ti chc nng hot ng

ca chng.

+ Vng tng cng khng mang tnh c trng cho tng gen m chng iu khin, c ngha hu nh cho mi gen.

+ Vng tng cng c tnh cht c trng rt yu gc phn loi. + mt s trng hp vng tng cng c tnh cht c trng cho tng m ca c th a bo bc cao. + Mt gen c th mang mt s vng tng cng. + Vng tng cng l on ADN ngn, mt vng tng cng c th cha 1 hoc mt vi tm trc.

3. Silencer (vng gy gim sao m)L nhng on ADN (nm thnh phn ADN khng m ho) c tc dng lm gim s sao m.

Tm li: sinh vt nhn chun nhng thnh phn tham giavo s iu ho hot ng ca gen operon phc tp hn nhiu so vi cu trc operon sinh vt nhn s. Hn na,

lng ADN m ho (exon) chim t l nh hn nhiu so vilng ADN khng m ho (intron v khong cch gia cc gen). b phn ADN ny nm di rc nhiu yu t tham gia vo s iu ho sao m.

2.4.2. iu ha sao m - s tng tc gia cc tc nhn iu ha vi enhancer v cc vng iu ha khc ca gen1. Tc ng ca cc hormone v protein iu ha sinh vt nhn chun bc cao c nhiu cht hormone c tc dng iu ha hot ng ca gen. Nhng t bo c cc cht hormone

(v d: nhm steroid, nhm glucocorticoit) ti tc ng gi l tbo ch. + Protein tip nhn (R) phi hp vi hormone steroid (H) to

thnh phc hp R - H, sau mt s bin i hnh dng protein,phc hp ny i vo nhn t bo. + Trong nhn t bo, phc hp protein tip nhn - hormone lin kt

vi nhng vng iu ha c trng: enhancer, promotor ca gen.T gy hiu qu kch thch sao m.

cc t bo ch ca dng hormone glucocorticoit, h thng tip nhn lm vic theo c ch sau: + Khi cha c hormone, protein tip nhn lin kt vi mt phn t c tn l Hsp90 v tn ti t bo cht. + Khi hormone glucocorticoit c mt, protein tip nhn lin kt vi n v y Hsp90 ra.

+ Phc hp protein tip nhn - hormone i vo nhn t bo, n lin kt vi mt on ca vng tng cng enhancer nm khng xa gen, on ny c tn gi l yu t phn ng vi glucocorticoit (GRE). S lin kt ny vo vng tng cng c tc ng kch thch promotor ca gen m n iu

khin, kt qu l sao m c tng.

2. C ch hot ng ca vng tng cng (enhancer)- Gi thuyt 1: enhancer l ch cho ARN polimerase hay cc yu t tham gia vo s sao m khc i vo, sau

c chuyn dch theo ADN v tm n promotor, sao m xyra. Gi thuyt ny khng p dng cho trng hp enhancer trong gen hay sau gen. - Gi thuyt 2: enhancer c th tng tc vi h thng khung ta ca nhn t bo s chuyn dch khng gian,

lm cho enhancer c gn vi cc yu t iu ho khcca gen. T , nhng qu trnh v tip nhn thng tin, truyn tn hiu sao m tr nn hiu qu hn.

- Gi thuyt 3: protein iu ho lin kt vi 1 enhancer mt tiu phn, tiu phn kia c th lin kt vi promotor hay vi mt protein ca enhancer khc gy hiu qu m, kch thch sao m ca ADN. - Sau khi enhancer tng tc vi cc protin in ho, n tr

thnh ch nng t dc theo si nhim sc xy ra 1lot cc qu trnh cng hng, gy nn nhng bin i lm bt n nh cc ht nucloxom, chng c gii phng ra khi si ADN to iu kin cho sao m xy ra.

2.5. T CHC CC GEN GENOM, HIN TNG KHUYCH I GEN 2.5.1. Cc gen n bn v cc gia nh gen, ngha Nu gen ch tn ti theo 1 bn b n bi NST th n

thuc nhm cc gen n bn. sinh vt bc cao, cc gen tn ti khng tun theo 1 bn m theo nhiu bn l ch yu, to nn gia nh gen. Gia nh gen l tp hp bao gm nhng gen ging nhau, thc hin nhng chc nng tng t, tc l n m ho nhng

protein ngun gc ging nhau.

Mt s kiu t chc gia nh gen:+ Kiu 1: cc gen lp li lin tc k lin tip nhau: cc bn gen c cu trc ging nhau, m ho cho mt sn phm ging nhau c lp li nhiu ln. Gm cc gen rARN , 5S ARN, cc gen histon VD: cc gen histon ca nhm bin : s bn sao lp li (H1, H4, H2B, H3, H2A): 300 600 + Kiu 2: trong cc thnh vin gen nm st nhau theo mt khi mt khu vc no ca genom, nhng khng to nn cc n v lp li ng nht nh kiu 1. VD1: cc gen - globin gm 7 thnh vin, chin khong 80000 i baz ca NST s 11. + Kiu 3: cc thnh vin khng to thnh khi nm lin nhau, m nm phn tn ri rc genome. C ch: ngay sau khi s nhn bn gen, xy ra qu trnh chuyn on cc gen c chuyn ti nhng ch mi. V d: thnh vin gen actin rui gim

Siu gia nh: Mt s gia nh gen to thnh mt tp on ln ti hng ngn bn gen, chim mt khu vc rt ln ca genom ti hng triu i nuclotit.

V d: Siu gia nh cc gen immunoglubulin gm:Cc gen immunoglubulin Cc gen kim tra s dung hp m

Kt lun: c im cu trc ca gen cng nh nhng kiu tchc cc gen genom ni ln tnh cht phc tp, tnh cht t chc tinh vi v thng nht cao trong s iu hnh hot ng ca cc gen gc nh tnh cng nh nh lng, din ra trong qu trnh pht trin c th ca sinh vt bc cao.

2.5.2. Hin tng khuych i gen, ngha- nhiu trng hp s lng bn gen c tng vt nn sovi s bn lp c trong genom - hin tng khuch i gen. V d: S khuch i gen rARN t bo non ca cc

Xenopus lavis: s lng bn gen rARN c trong genom khong600 bn, sau khuch i tng ln 2.106 bn. - qu trnh khuch i, nhng bn gen rARN c tch ra

khi NST v to thnh nhng vng nh. Cc vng ny ti bntheo c ch vng ln to nn s lng rt ln cc bn gen rARN.

Nh vy, khuch i gen l hin tng ph bin sinh vt. Nl mt trong nhng c ch thch ng, tr li theo c ch t ng nhng giai on pht trin c th no , hoc c th

xy ra do tc ng ca yu t mi trng.

2.6. CC YU T DI TRUYN DI NG TRONG GENOM2.6.1. Khi nim, s pht hin ra yu t di truyn di ng Yu t di truyn di ng (Transposalle genetic elemets, TGE) c B.Clintock (1947) pht hin khi nghin cu nhng bin ng di truyn nh hng ti s t nhim sc th ng. pht hin ra mt yu t di ng - locus Ds (yu t phn tn), d xy ra s t nhim sc th. Tuy nhin, hot

tnh di ng ca yu t Ds ch xut hin khi trong genom cmt yu t di ng th 2, c tn gi l yu t hot ha (k hiu Ac).

TH NGHIM CA B.CLINTOCK+ S dng mt gen ch th kim sot s tch t sc t trong aleurone (lp ngoi cng ca ni nh ht ng). Gen ch th ny l mt alen ca locus C trn NST 9. V alen ny (C1) l mt yu t c ch tri i vi mu sc ca aleurone - ht ng mang alen ny khng mu. + Th phn cho cy CC bng ht phn ca bng c C1C1 - ht ng c ni nh C1CC - hu ht khng mu, ch c mt t m c mu. Nh vy, alen C1 i khi khng c mt trng s pht trin ni nh, dn ti mt dng t bo v cc t chc c kh nng to thnh sc t, kiu gen y s l CC, trong c phn nh mt alen C1 alen ny mt l do t gy NST.

+ Khi Ds (yu t di ng) nm cnh locus C n b bt hot ha (C- C1 ) - ht khng mu. + Nu trong kiu gen c mt yu t Ac do c chuyn dch locus C tr li hot tnh cc ht c vt mu. Kt lun: yu t di truyn di ng l nhng on ADN c

bit, xen vo 1 hoc 1 s v tr trong h gen, to nn ccbin i di truyn. Cc bin i ny s mt i khi TGE ri khi v tr xen.

S din t s tc ng ca cc yu t Ds v Ac ti s hot ng ca locus C

2.6.2. Cc yu t di truyn di ng vi khun, ngha vi khun pht hin ra nhng dng t bin c bit c c im chung l cnh chng c mt on ADN xen vo.

Nhng on ADN ny gi l cc on xen - IS (insertionsequences). c im ca on xen: + Hai u mt c trt t baz ging ht nhau, nhng xp ngc chiu nhau, c di khong 9 - 40 i baz. + Hu ht cc on IS cha gen kim tra enzyme transporase - kim tra s di ng ca chng. + trong on IS c th cha nhng im khi u v kt thc dch m, v cha on ADN gy tn hiu kt thc sao m.

+ im xen ca on IS trn nhim sc th (im ch),

hai pha ca n pht hin thy hai trt t lp c ln t4 - 9 i baz. l v trong qu trnh xen, im ch xy ra s t theo kiu ziczac trn hai si ca chui kp ADN. Sau khi on IS xen vo, xy ra s tng hp lp ch trng, kt qu l thu c hai trt t lp hai pha ca on xen.

Cu trc on xen v s xen ca n

2.6.2. Cc yu t di truyn di ng sinh vt nhn chun, on xen, c ch xen, cc c ch chuyn v sinh vt nhn chun pht hin ra nhiu yu t di truyn di ng nhng i tng nghin cu in hnh nh

nm men, rui, ng C ch xen: + Yu t di ng (transposon) c tch ra khi ADN cho

n ch mi (ADN) nhn theo c ch ti t hp tng nggia hai trt t lp hai u ca n. + Xy ra c ch sao chp ngc (retrotransposon): ADN ca yu t di ng sao ra thnh ARN, t , nh enzyme sao chp ngc to bn ADN ca n, v chuyn ti ch mi. + Cc yu t di ng c c ti bn (s chuyn v sao chp), tip theo l s di ng ca chng.

2.6.4. ngha ca cc yu t di truyn di ng Xut hin 1 s t bin thun nghch di s kim sot ca yu t di ng. Cc yu t di ng c th gy s t NST- sp xp

li cc on trn NST, ci bin cu trc NST. Yu t di ng c th l vt trung gian ca s ti t hp ADN, c vai tr trong s lp ghp cc trn trn NST - ng dng trong chuyn np gen.

Pht hin v tr ca gen nghin cu trn NST nh yu t di ng (gen t bin c eo th nh yu t di ng). Yu t di ng cung cp mt s thnh phn iu hagen tng cng sao m S vn ng ca yu t di ng xy ra vi tn s rt

thp. S tng tn s vn ng ca chng c lin quanti ga tr thch ng ca c th. Yu t di ng c th t ti bn lan truyn trong

genom ca t bo - yu t di ng c coi nh yu tk sinh genom, s dng b my ti bn ca t bo ch.