B GIO DC V O TO TRNG I HC NNG LM THNH PH H CH MINH

B MN CNG NGH SINH HC

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BO CO

SINH HO I CNGSINH TNG HP PROTEINGing vin hng dn: L Th Bnh PhngSinh vin thc hin:

Hunh V Linh

11126153

Nguyn Ngc Thch12126366

Lng Vn Hng12126168

Dip Minh Tn

Phm Ngc cThng 8 nm 2014MC LC

Chng 1: TNG QUAN V QU TRNH SINH TNG HP PROTEIN1.1. nh ngha: L qu trnh hnh thnh mt protein mi t nhiu amino acid vi thnh phn v trt t sp xp c qui nh theo mt m nht nh m trch mt nhim v tng ng vi m .1.1.1. Phin m: L qu trnh truyn truyn t thng tin di truyn t phn t ADN mch kp sang ARN mch n. Qu trnh phin m ch xy ra trn mt mch ca gen, mch ny gi l mch gc1.1.2. Dch m: Dch m l qu trnh tng hp chui polypeptide da trn cc thng tin m ha trn mRNA v trnh t sp xp cc axit amin trn si polypeptide 1.2. S khc nhau v qu trnh sinh tng hp protein Prokaryotes v Eukaryotes

ProkaryoticEukaryote

Mt loi RNA polymerase

mRNA c dch m tng hp protein ngay sau phin m

mRNA m ha cho nhiu chui polypeptide (polycistronic) Din ra ng thi trong t bo cht Khi ng nhanh Nhiu loi ARN polymerase

RNA polymerase I: rRNA

RNA polymerase II: mRNA

RNA polymerase III: tRNA, RNA 5S

mRNA khng dch m ngay thnh protein m chu mt s bin i ha hc

rRNA hnh thnh trong nhn di dng phn t tin thn (precursor) 45S phn ct thnh 18S, 28S v 5,8Schuyn ra t bo cht

RNA tng hp trong nhn, dch m to protein din ra t bo cht

S khi ng phin m phc tp do cu trc cht ch gia histon-DNA

Chng 2 QU TRNH SINH TNG HP PROTEIN

2.1. Phin m:Qu trnh ny c nhiu tn gi: phin m, tng hp ARN, sao m...nh ngha nh vy khng c ngha rng tt c cc on ADN u s c phin m tr thnh ARN. Ch c gen (nh ngha pha trn) mi c phin m.Qu trnh phin m ch xy ra trn 1 mch ca gen, mch ny c gi l mch gc.2.1.1 Yu t tham gia- Enzim: cn nhiu enzim khc nhau, v cc yu t tr gip. Vai tr chnh l ca ARN polimeraza (ARN pol)- Khun: 1 mch ca ADN. Chiu tng hp mch mi t 5'-3'.- Nguyn liu: Cc riboNu v ngun cung cp nng lng (ATP, UTP, GTP...)2.1.2. Din bina. M u:- ARN pol nhn bit im khi u phin m.Vic ARN pol nhn bit im khi u phin m ca 1 gen l cc k quan trng i vi s phin m ca gen. 1 khi ARN pol bm vo ADN, gn nh chc chn n s phin m. ARN pol th lun r sot dc si ADN, trong khi gen th c gen c phin m nhiu, gen phin m t. Cn bn ca s khc nhau ny l ci gi l i lc ca gen i vi ARN pol. i lc cng cao, gen cng c nhiu ARN pol chy qua, cng nhiu phn t protein c tng hp. i lc ny ph thuc vo hng lot protein, v c bit l trnh t vng iu ha ca gen.- ADN tho xon, tch mch ti v tr khi u phin m.- Cc riboNu ti v tr ADN tch mch, lin kt vi ADN mch khun theo nguyn tc b sung, c th:A (ADN) lin kt vi U mi trng (mt)T (ADN) lin kt vi A mtG (ADN) lin kt vi C mtC (ADN) lin kt vi G mt- Hnh thnh lin kt photphoieste gia cc riboNu -> to mch.b. Ko di:- ARN pol di chuyn trn mch gc theo chiu 3'-5', c nh th, cc riboNu lin kt to thnh phn t ARN.- ARN tch dn khi mch ADN, 2 mch ADN sau khi ARN pol i qua li lin kt tr li.c. Kt thc:Nh tn hiu kt thc, ARN pol kt thc vic tng hp ARN, ri khi ADN.Phn t ARN c to ra sinh vt nhn s, qua 1 vi s ch nh c th lm khun tng hp protein. Trn thc t, sinh vt nhn s, qu trnh phin m (tng hp mARN) v qu trnh dch m (tng hp protein) gn nh xy ra ng thi.Cn sinh vt nhn thc, do gen l gen phn mnh (c xen k exon v intron), nn phn t ARN c to ra c c on tng ng intron, exon. Phn t ny c gi l tin mARN. Tin mARN s c ct b cc intron to thnh phn t mARN trng thnh. Phn t mARN trng thnh ny mi lm khun tng hp protein.Vic ct b intron kh phc tp. Cn c nhng on trnh t c bit phc h ct intron c th nhn bit c. Do vy, nu c t bin xy ra lm thay i trnh t ny, khin phc h ct intron khng nhn ra intron, khng ct intron, u c th dn n thay i cu trc protein. V vy, khng hon ton ng khi ni rng t bin intron l khng gy hi.Sau khi ct intron, vic sp xp li cc exon cng l vn . S sp xp khc nhau c th dn n cc phn t mARN trng thnh khc nhau, v ng nhin l quy nh cc protein khc nhau. y l 1 hin tng c thy i vi gen quy nh tng hp khng th ngi. V vy, ch 1 lng rt nh gen nhng c th tng hp rt nhiu loi khng th khc nhau. sinh vt nhn thc, h enzim phc tp hn, c nhiu loi ARN pol tng hp tng loi mARN, tARN, rARN.2.2. Dch m2.2.1. M di truynDo chi c bn loai nucleotide khc nhau trong mRNA v c n 20 loai amino acid trong protein nn s dich m khng th c thc hin theo kiu tng ng mt nucleotide - mt amino acid c. Ngi ta giai m ton b cc amino acid vo nhng nm u cua thp ky 1960. Mi amino acid c m ha bi ba nucleotide lin tip trn DNA (hoc RNA tng ng), b ba nucleotide ny c goi l mt codon. Vi 4 loai nucleotide khc nhau se c 43 = 64 codon khc nhau c phn bit bi thnh phn v trt t cua cc nucleotide. Trong s ny c 3 codon kt thc l UAA, UAG v UGA c nhim vu bo hiu chm dt vic tng hp chui polypeptide. Trong 61 m cn lai c nhiu codon cng m ha cho mt amino acid.

Cc codon c oc theo hng 5'3'. V vy chui m ha cho dipeptide NH2- Thr-Arg-COOH c vit l 5'-ACGCGA-3'. Cc codon khng chng ln nhau v vng dich m cua mRNA khng cha cc khoang trng.

2.2.2. Cc ribosomeRibosome l b my ai phn t iu khin s tng hp protein. N c cu tao bi t nht l ba phn t RNA v hn 50 protein khc nhau, vi trong lng phn t l 2,5 MDa (megadalton) i vi ribosome cua prokaryote v 4,2 MDa i vi ribosome cua eukaryote.

2.2.2.1. Thnh phn cu tao cua ribosomeMi ribosome bao gm mt tiu n vi ln v mt tiu n vi nho. Tiu n vi ln cha trung tm peptidyl transferase chiu trch nhim cho vic hnh thnh cc cu ni peptide. Tiu n vi nho cha trung tm giai m, l ni cc tRNA c gn amino acid oc v giai m cc codon. Ngoi ra cn c trung tm gn cc yu t tiu n vi ln.

Theo quy c, cc tiu n vi c t tn theo tc lng cua chng di lc ly tm. n vi o tc lng l Svedberg v c vit tt l S. Ribosome cua prokaryote l ribosome 70S, trong tiu n vi ln l 50S v tiu n vi nho l 30S. Ribosome cua eukaryote l 80S, vi tiu n vi ln l 60S v tiu n vi nho l 40S.

Mi tiu n vi u c cu tao bi cc RNA ribosome (rRNA) v cc protein ribosome. n vi Svedberg lai c s dung phn bit cc rRNA (Bang 2.1).Bang 2.1. Cc thnh phn cu tao cua ribosome.

Cc thnh phn cu toProkaryotes

Tiu n v ln (50S)Tiu n v nh (30S)Tiu n v ln (80S)Tiu n v nh (40S)

rRNrRNA 5S (120 Nu)

rRNA 23S (2900 Nu)

rRNA 16S (1540 Nu)

rRNA 5,8S (160 Nu)

rRNA 5S (120 Nu)

rRNA 28S (4700 Nu)

rRNA 18S (1900 Nu)

ProteiAn34 protein21 Protein39 protein33 protein

Trong qu trnh dich m, tiu n vi ln v tiu n vi nho cua mi ribosome lin

kt vi nhau v vi mRNA. Sau mi vng tng hp protein, chng lai ri nhau ra.

2.2.2.2. Cc vi tr gn tRNA trn ribosomeTrn ribosome cha ba vi tr gn tRNA l vi tr A, P v E. Trong :

A l vi tr gn aminoacyl-tRNA (tRNA c mang amino acid).

P l vi tr gn peptidyl-tRNA (tRNA c mang chui polypeptide).

E l vi tr gn tRNA m c phng thch sau khi chui polypeptide c chuyn sang aminoacyl-tRNA.

Mi vi tr gn tRNA c hnh thnh tai giao din gia tiu n vi ln v tiu n vi nho. Bng cch ny, cc tRNA c gn vo c th bt ngang qua khoang cch gia trung tm peptidyl transferase cua tiu n vi ln v trung tm giai m cua tiu n vi nho. u 3' cua tRNA c nm gn tiu n vi ln v vng i m gn tiu n vi nho.

Hnh 2.1. Cc thnh phn chc nng cua ribosome.2.2.2.3. Cc knh cua ribosome l cc knh cho php mRNA i vo v i ra khoi ribosome, v knh cho php chui polypeptide mi sinh i ra khoi ribosome. mRNA i vo v i ra khoi trung tm giai m cua ribosome thng qua hai knh hep tai tiu n vi nho. Trong , knh vo c chiu rng chi u cho RNA khng bt cp i qua. c im ny am bao cho mRNA c dui thng khi n i vo trung tm giai m, bng cch loai bo moi tng tc bt cp base b sung ni phn t.

Mt knh xuyn qua tiu n vi ln tao li thot cho chui polypeptide mi c tng hp. Kch thc cua knh han ch c s gp cua cc chui polypeptide ang tng hp. V vy, protein chi c th hnh thnh cu trc bc ba sau khi n c giai phng khoi ribosome.

2.2.3. S hnh thnh aminoacyl - tRNA2.2.3.1. Ban cht cua s gn amino acid vo tRNAQu trnh gn amino acid vo tRNA l qu trnh hnh thnh mt lin kt acyl gia nhm carboxyl cua amino acid v nhm 2'- hoc 3'-OH cua adenine u 3' cua tRNA. Lin kt ny c xem l mt lin kt giu nng lng. Nng lng giai phng ra khi lin kt bi ph v gip hnh thnh cu ni peptide lin kt amino acid vi chui polypeptide ang c tng hp.

2.2.3.2. S nhn din v gn amino acid vo tRNAS nhn din v gn amino acid vo tRNA tng ng c thc hin bi mt enzyme goi l aminoacyl-tRNA synthetase.

Qu trnh ny din ra nh sau: u tin, amino acid c adenylyl ha bng cch phan ng vi ATP, kt qua tao thnh amino acid c gn adenylic acid qua cu ni ester giu nng lng gia nhm COOH cua amino acid v nhm phosphoryl cua AMP, ng thi giai phng ra pyrophosphate. Sau , amino acid c adenylyl ha ny (vn ang gn vi synthetase) phan ng tip vi tRNA. Phan ng ny chuyn amino acid n u 3' cua tRNA gn vi nhm OH, ng thi giai phng AMP.

Phan ng tng hp cua qu trnh ny nh sau:

Amino acid + tRNA + ATP aminoacyl - tRNA + AMP + PPi2.2.3.3. Tnh c hiu cua aminoacyl - tRNA synthetaseHu ht cc t bo u c mt enzyme synthetase ring bit chiu trch nhim cho vic gn mt amino acid vo mt tRNA tng ng (nh vy c tt ca 20 synthetase). Tuy nhin, nhiu vi khun c di 20 synthetase. Trong trng hp ny, cng mt synthetase chiu trch nhim cho hn mt loai amino acid.

S nhn din amino acid chnh xc l da vo kch thc, s tch in v gc R khc nhau cua cc amino acid. S nhn din tRNA da vo cc trnh t nucleotide khc nhau cua tRNA. Ty l sai st trong qu trnh gn amino acid vi tRNA tng ng l kh thp.

2.2.3.4. Phn loai aminoacyl - tRNA synthetaseC hai loai tRNA synthetase.

Loai I bao gm cc synthetase gn cc amino acid nh Glu, Gln, Arg, Cys, Met, Val, Ile, Leu, Tyr, Trp vo nhm 2'-OH.

Loai II gm cc synthetase gn cc amino acid nh Gly, Ala, Pro, Ser, Thr, His, Asp, Asn, Lys, Phe vo nhm 3'-OH.

2.2.4. Cc giai oan cua qu trnh dich mQu trnh dich m c bt u bng s gn cua mRNA v mt tRNA khi u vi tiu n vi nho t do cua ribosome. Phc hp tiu n vi nho-mRNA thu ht tiu n vi ln n tao nn ribosome nguyn ven vi mRNA c kep gia hai tiu n vi. S tng hp protein c bt u tai codon khi u u 5' cua mRNA v tin dn v pha 3'. Khi ribosome dich m t codon ny sang codon khc, mt tRNA gn amino acid k tip c a vo trung tm giai m v trung tm peptidyl transferase cua ribosome. Khi ribosome gp codon kt thc th qu trnh tng hp chui polypeptide kt thc. Chui ny c giai phng, hai tiu n vi cua ribosome ri nhau ra v sn sng n gp mRNA mi thc hin mt chu trnh tng hp protein mi. Qu trnh dich m c chia thnh ba giai oan l khi u, ko di v kt thc.2.2.4.1. Giai oan khi u2.2.4.1.1. prokaryote* Cc yu t khi u (IF: initiation factor)

C cc yu t khi u xc tc cho tiu n vi nho trong vic hnh thnh phc hp khi u. l IF1, IF2, IF3. Mi yu t khi u c tc dung nh sau:

IF1 gip tiu n vi nho gn vo mRNA v ngn can cc tRNA gn vo vng thuc vi tr A trn tiu n vi nho.

IF2 l mt protein gn v thuy phn GTP. IF2 thc y s lin kt gia fMet- tRNAifMet v tiu n vi nho, ngn can nhng aminoacyl-tRNA khc n gn vo tiu n vi nho.

IF3 ngn can tiu n vi nho ti lin kt vi tiu n vi ln v gn vi cc tRNA mang amino acid. IF3 gn vo tiu n vi nho vo cui vng dich m trc, n gip tch ribosome 70S thnh tiu n vi ln v tiu n vi nho.

Khi tiu n vi nho c gn ba yu t khi u, n se gn tRNA khi u v mRNA. S gn hai RNA ny l hon ton c lp vi nhau.

* Bc 1: Tiu n vi nho gn vo codon khi u

S lin kt gia tiu n vi nho vi mRNA c thc hin thng qua s bt cp base b sung gia vi tr gn ribosome v rRNA 16S. Cc mRNA cua vi khun c mt trnh t nucleotide c hiu goi l trnh t Shine-Dalgarno (SD) gm 5-10 nucleotide trc codon khi u. Trnh t ny b sung vi mt trnh t nucleotide gn u 3' cua rRNA 16S. Tiu n vi nho c t trn mRNA sao cho codon khi u c t ng vo vi tr P mt khi tiu n vi ln gn vo phc hp.

* Bc 2: tRNA u tin c mang methionine bin i n gn trc tip vi tiu n vi nho

Mt tRNA c bit c goi tRNA khi u n gn trc tip vi vi tr P (khng qua vi tr A). tRNA c anticodon (b ba i m) c th bt cp vi AUG hoc GUG. Tuy nhin tRNA ny khng mang methionine cung nh valine m mang mt dang bin i cua methionine goi l N-formyl methionine. tRNA khi u ny c goi l fMet-tRNAifMet.

Trong hoc sau qu trnh tng hp polypeptide, gc formyl c loai bo bi enzyme deformylase. Ngoi ra, aminopeptidase se loai bo methionine cung nh mt hoc hai amino acid k tip u chui polypeptide.

* Bc 3: Hnh thnh phc hp khi u 70S

Bc gn thm tiu n vi ln tao thnh phc hp khi u 70S din ra nh sau: khi codon khi u v fMet-tRNAifMet bt cp vi nhau, tiu n vi nho thay i hnh dang lm giai phng IF3. S vng mt IF3 cho php tiu n vi ln gn vo tiu n vi nho ang mang cc thnh phn trn. Nh c tiu n vi ln gn vo, hoat tnh GTPase cua IF2-GTP c kch thch thuy phn GTP. IF2-GDP tao thnh c i lc thp i vi ribosome v tRNA khi u dn n s giai phng IF2- GDP cung nh IF1. Nh vy phc hp khi u cui cng c tao thnh bao gm ribosome 70S c gn tai codon khi u cua mRNA, vi fMet-tRNAifMet tai vi tr P, cn vi tr A ang trng. Phc hp ny sn sng tip nhn mt tRNA mang amino acid vo vi tr A bt u tng hp polypeptide.

Hnh 2.2. Khi u dich m prokaryote.

2.2.4.1.2. Eukaryote* Bc 1: S hnh thnh phc hp tin khi u 43SGiai oan khi u i hoi s h tr cua hn 30 protein khc nhau, mc d eukaryote cung c nhng yu t khi u tng ng vi prokaryote. Cc yu t khi u ny c k hiu l eIF.

Hnh 2.3. Khi u dich m eukaryote.Khi ribosome cua eukaryote hon thnh mt chu trnh dich m, n tch ri ra thnh tiu n vi ln v tiu n vi nho t do thng qua tc ng cua cc yu t eIF3 v eIF1A (tng t vi IF3 prokaryote). Hai protein gn GTP l eIF2 v eIF5B lm trung gian thu ht tRNA khi u gn methionine (ch khng phai N-formyl methionine nh prokaryote) n tiu n vi nho. Chnh yu t eIF5B-GTP l tng ng vi IF2-GTP cua prokaryote. Yu t ny lin kt vi tiu n vi nho theo phng thc phu thuc eIF1A. Ri eIF5B-GTP gip thu ht phc hp eIF2-GTP v Met-tRNAiMet n tiu n vi nho. Hai protein gn GTP ny cng nhau a Met-tRNAiMet vo vng thuc vi tr P cua tiu n vi nho. Kt qua, hnh thnh phc hp tin khi u 43S.

* Bc 2: S nhn dang mu 5' cua mRNA

Qu trnh ny c thc hin thng qua eIF4F. Yu t ny c ba tiu n vi, mt tiu n vi gn vo mu 5', hai tiu n vi khc gn vi RNA. Phc hp ny lai c gn vi eIF4B lm hoat ha mt enzyme RNA helicase cua mt trong nhng tiu n vi cua eIF4F. Helicase ny tho xon tt ca cc cu trc bc hai c hnh thnh u tn cng cua mRNA. Phc hp eIF4F/B v mRNA lai thu ht phc hp tin khi u 43S n thng qua tng tc gia eIF4F v eIF3.

* Bc 3: Tiu n vi nho tm thy codon khi u bng cch qut xui dng t u 5' cua mRNA v s hnh thnh phc hp khi u 80S

Mt khi c gn vo u 5' cua mRNA, tiu n vi nho v cc yu t lin kt vi n di chuyn doc theo mRNA theo hng 5' 3' cho n khi gp trnh t 5'-AUG-3' u tin m n nhn dang l codon khi u. Codon c nhn dang bng s bt cp base b sung gia anticodon (b ba i m) cua tRNA khi u v codon khi u. S bt cp ny thc y phng thch eIF2 v eIF3 cho php tiu n vi ln gn c vo tiu n vi nho. S gn ny dn n phng thch cc yu t khi u cn lai thng qua s thuy phn GTP di tc dung cua eIF5B. Cui cng, Met-tRNAiMet c a vo vi tr P cua phc hp khi u 80S. Lc ny, ribosome trong t th sn sng tip nhn aminoacyl-tRNA vo vi tr A.* Nhng yu t khi u dich m gi mRNA eukaryote dang vng

Ngoi vic gn vo u 5' cua mRNA, cc yu t khi u cn lin kt cht che vi u 3' thng qua ui poly (A). iu ny c thc hin bi s tng tc gia eIF4F v protein gn poly (A) boc bn ngoi ui poly (A). Vic tm thy cc yu t khi u dich m c vai tr "vng ha" mRNA theo phng thc phu thuc ui poly (A) giai thch c quan st trc y l mt khi ribosome kt thc s dich m mt mRNA m c vng ha thng qua ui poly (A) th ribosome mi c phng thch ny l ribosome l tng ti khi u dich m trn cng mRNA.2.2.4.2. Giai oan ko di2.2.4.2.1. Bc 1: Aminoacyl - tRNA c a n vi tr A nh yu t ko di EF - TuMt khi tRNA gn amino acid th EF - Tu n gn vo u 3' cua aminoacyl - tRNA. EF - Tu chi c th gn vi aminoacyl - tRNA khi n lin kt vi GTP. EF Tu - GTP a aminoacyl - tRNA vo vi tr A cua ribosome. Chi phc hp aminoacyl tRNA EF Tu - GTP no c anticodon b sung vi codon cua mRNA tai vi tr A th mi c gi lai trn ribosome. Sau , EF - Tu tng tc vi trung tm gn yu t cua ribosome nm trn tiu n vi ln v thuy phn GTP, ri EF-Tu c phng thch khoi tRNA v ribosome, aminoacyl - tRNA nm lai tai vi tr A.

Hnh 2.4. Ko di dich m.

2.2.4.2.2. Bc 2: Hnh thnh cu ni peptideAminoacyl - tRNA tai vi tr A c quay vo trung tm peptidyl transferase v cu ni peptide c hnh thnh. Phan ng ny c xc tc bi peptidyl transferase, ngy nay n c xc inh l rRNA, c bit l rRNA 23S cua tiu n vi ln. V vy, peptidyl transferase cn c goi l ribozyme.

Trong qu trnh hnh thnh cu ni peptide, cu ni gia amino acid v tRNA vi tr A khng bi ph v. u 3' cua ca hai tRNA c a n gn nhau v nhm amine cua amino acid vi tr A tn cng nhm carboxyl cua amino acid vi tr P. Kt qua l tRNA vi tr A mang mt dipeptide, trong khi tRNA vi tr P bi kh acyl.

Sau xay ra s chuyn dich (xem bc 3): peptidyl - tRNA (ang mang dipeptide) chuyn sang vi tr P, v vi tr A sn sng tip nhn mt aminoacyl - tRNA mi. Cu ni peptide tip theo c hnh thnh theo cch ging ht trn, trong nhm amine cua amino acid mi lin kt vi nhm carboxyl u C tn cng cua chui polypeptide ang tng hp. Thc cht, y l qu trnh chuyn chui polypeptide ang tng hp t peptidyl - tRNA vi tr P sang aminoacyl - tRNA vi tr A. V vy, phan ng tao cu ni peptide c goi l phan ng peptidyl transferase.

Nh vy, chui polypeptide c tng hp theo chiu t u N n u C.

Trong qu trnh ny, khng c s thuy phn nucleoside triphosphate. Nng lng c cung cp t s ph v cu ni acyl giu nng lng gia chui polypeptide ang tng hp v tRNA.

2.2.4.2.3. Bc 3: S chuyn dich (translocation)Mt khi phan ng peptidyl transferase xay ra th tRNA trong vi tr P khng gn vi amino acid na, v chui polypeptide ang hnh thnh c lin kt vi tRNA trong vi tr A. mt vng ko di polypeptide mi xay ra, tRNA vi tr P phai chuyn n vi tr E v tRNA vi tr A chuyn n vi tr P. ng thi, mRNA phai di chuyn qua 3 nucleotide ribosome tip xc vi codon tip theo. Nhng s di chuyn ny c goi l s chuyn dich.

Bc u tin trong chuyn dich c song hnh vi phan ng peptidyl transferase. Khi chui peptide c chuyn sang tRNA vi tr A, u 3' cua tRNA ny hng n vng vi tr P cua tiu n vi ln, trong khi u anticodon vn cn nm vi tr A. Tng t, tRNA vi tr P (m khng cn gn chui polypeptide na) nm vi tr E cua tiu n vi ln v vi tr P cua tiu n vi nho.

hon thnh s chuyn dich phai c s tc ng cua mt yu t ko di goi l EF - G. EF - G chi gn vo ribosome khi c lin kt vi GTP. Sau khi phan ng peptidyl transferase xay ra, s thay i vi tr cua tRNA vi tr A l vi tr gn cho EF - G. Khi EF G - GTP gn vo vi tr ny, n tip xc vi trung tm gn yu t v kch thch thuy phn GTP. S thuy phn ny lm thay i hnh dang cua EF G - GDP v cho php n vi ti tiu n vi nho thc y s chuyn dich cua tRNA vi tr A. Khi s chuyn dich c hon thnh, cu trc cua ribosome giam ng k i lc vi EF G - GDP, iu ny cho php yu t ko di c phng thch khoi ribosome. Cng vi vic tRNA vi tr A chuyn n vi tr P, tRNA vi tr P chuyn n vi tr E v mRNA dich chuyn ba nucleotide. T vi tr E, tRNA c phng thch khoi ribosome.

2.2.4.2.4. Cc yu t ko di c gn GDP (EF Tu - GDP v EF G - GDP) c i GDP thnh GTP trc khi tham gia vo vng ko di miEF - Tu v EF G l nhng protein xc tc m chi c s dung mt ln i vi mt vng ko di bao gm a tRNA vo ribosome, hnh thnh cu ni peptide, v chuyn dich. Sau khi GTP c thuy phn, hai protein trn phai giai phng GDP v gn vi mt GTP mi. i vi EF - G, do GDP c i lc thp vi EF - G hn GTP nn GDP nhanh chng c giai phng v GTP mi c gn vo.

i vi EF - Tu, cn c s tham gia cua yu t hon i GTP goi l EF - Ts. Sau khi EF Tu - GDP c phng thch khoi ribosome, EF - Ts c gn vo EF - Tu v th ch cua GDP. Sau GTP n gn vo phc hp EF Tu EF - Ts. Phc hp sau cng c tch thnh EF - Ts t do v EF Tu - GTP.

2.2.4.3. Giai oan kt thc2.2.4.3.1. Cc yu t giai phng kt thc dich mChu ky gn aminoacyl - tRNA cua ribosome, s hnh thnh cu ni peptide, v s chuyn dich xay ra lin tuc cho n khi mt trong ba codon kt thc vo vi tr A. Cc codon ny c nhn din bi cc yu t giai phng (RF: release factor).

C hai loai yu t giai phng:

Cc yu t giai phng loai I nhn din codon kt thc v thc y s thuy phn tch chui polypeptide ra khoi peptidyl - tRNA tai vi tr P. Prokaryote c hai yu t giai phng loai I l RF1 v RF2, trong RF1 nhn din codon kt thc UAG v RF2 nhn din UGA, cn UAA c nhn din bi ca RF1 v RF2. Eukaryote chi c mt yu t giai phng goi l eRF1 nhn din c ca ba loai codon kt thc.

Cc yu t giai phng loai II kch thch s tch yu t giai phng loai I ra khoi ribosome sau khi chui polypeptide c giai phng. Chi c mt yu t giai phng loai II, c goi l RF3 prokaryote v eRF3 eukaryote. Yu t giai phng loai II c iu ha bi GTP.

Hnh 2.5. Kt thc dich m2.2.4.3.2. S hon i GDP/GTP v thuy phn GTP iu khin hoat ng cua yu t giai phng loai IIYu t giai phng loai II l mt protein gn GTP nhng c i lc vi GDP cao hn GTP. V vy, phn ln RF3 c gn vi GDP. RF3 - GDP gn vi ribosome theo mt phng thc phu thuc s hin din cua yu t giai phng loai I. Sau khi yu t giai phng loai I kch thch s phng thch chui polypeptide, xay ra mt s thay i hnh dang ribosome, v yu t giai phng loai I kch thch RF3 hon i GDP thnh GTP. S gn GTP vo RF3 dn n s hnh thnh tng tc i lc cao vi ribosome v y yu t giai phng loai I ra khoi ribosome. S thay i ny cho php RF3 lin kt vi trung tm gn yu t cua tiu n vi ln. S tng tc ny kch thch thuy phn GTP. V khng cn yu t loai I na nn RF3 - GDP c i lc thp vi ribosome v bi phng thch ra ngoi.

2.2.4.3.3. S ti tun hon cua ribosomeSau khi phng thch chui polypeptide v cc yu t giai phng, ribosome vn cn gn vi mRNA cng vi hai tRNA tai vi tr P v vi tr E. ribosome tham gia vo qu trnh tng hp polypeptide mi, tRNA v mRNA phai i khoi ribosome v hai tiu n vi cua ribosome phai ri nhau ra. Tp hp nhng s kin nh vy goi l s ti tun hon ribosome (ribosome recycling).

prokaryote, c mt yu t goi l yu t ti tun hon ribosome (RRF: ribosome recycling factor). RRF gn vo vi tr A, n bt chc tRNA. RRF li ko EF - G n ribosome v EF - G kch thch giai phng nhng tRNA tai vi tr P v E. Sau , EF - G v RRF c phng thch khoi ribosome cng vi mRNA. IF3 c th tham gia vo s giai phng mRNA ng thi n cung cn cho s tch ri hai tiu n vi cua ribosome. Kt qua tao ra tiu n vi nho gn IF3 v tiu n vi ln t do. Ribosome by gi c th tham gia vo vng dich m mi.

2.3. Hu dch m (Post - Translation)iu ha hot tnh protein bng cc bin i sau dch m

Cc phc hp protein hnh thnh sau dch m:

Proteinlipidlipoprotein

Proteingc carbonhydrateglycoprotein

Proteinion kim loimetalloprotein

S bin i ca amino acid gm: s methyl ha, acetyl ha, ubiquitin ha, phosphoryl ha (enzyme kinase)

S phosphoryl ha c th lm protein thay i hnh dng, hnh thnh phn ly cc phc hp.

iu ho d lp th (allostericregulation). S gn vo protein ca mt ligand (thng l mt phn t nh ng/amino acid) dn n s thay i cu hnh ca protein .

S hot ho kinase ph thuc cyclin (CDKs) l mt v d in hnh v iu ho sau dch m. Hot ng CDK c iu khin bi qu trnh phosporyl ho v iu ho d lp th thng qua tng tc gia enzyme v mt protein iu ho gi l cyclin.

Hnh 2.6. Cc mc iu chnh hot ng ca protein

Hnh 2.7. S phosphoryl ha protein

CHNG 3: T BIN

I. t bin gene

t bin gene l nhng bin i xy ra bn trong cu trc gene. Mi t bin gene dn n s thay i trnh t nucleotide to ra cc allele khc nhau. t bin gene c th xy ra do bin i ca trnh t nucleotide trong gene. t bin gene khng pht hin c khi quan st t bo hc.

Trong t nhin, tt c cc gene u c t bin c gi l t bin t nhin hay ngu pht (spontaneous mutation). Cc t bin t nhin thng xut hin rt t.

1. Cc kiu t bin gene

t bin gene hay t bin im: l cc bin i rt nh trn mt on DNA, thng lin quan n mt cp base n ca DNA hoc mt s t cp base k nhau. t bin im lm thay i gene kiu di (wild-type gene),. Thc t t bin im hu nh lm gim hoc lm mt chc nng ca gene hn l lm tng cng chc nng ca gene.

V ngun gc, t bin im c phn ra lm t bin ngu nhin (spontaneous) v t bin cm ng (induced).

t bin cm ng: l dng t bin xut hin vi tn s t bin tng ln khi x l c mc ch bng tc nhn t bin hoc tc nhn mi trng c bit. t bin ngu nhin l t bin xut hin khi khng c s x l ca tc nhn t bin. t bin ngu nhin c tnh l t l c s ca t bin v c dng c chng ngun bin d di truyn t nhin trong qun th. Tn s t bin ngu nhin thp nm trong khong 10-5 - 10-8, v vy t bin cm ng l ngun t bin quan trng cho phn tch di truyn.

Tc nhn t bin c s dng ph bin l ngun chiu x nng lng cao (high-energy radiation) hoc cc ha cht c bit.

Cc dng t bin im: c hai dng t bin im chnh trong phn t DNA:

+ t bin thay th cp base (base substitution)

+ t bin thm bt cp base (base insertion - base delection)

Cc t bin ny c th pht sinh do nh hng ca mi trng nh nh hng ca cc tc nhn gy t bin.

1.1. t bin thay th cp base

Kiu t bin n gin nht l thay th mt base, trong mt cp nucleotide trong gene c thay th bng mt cp nucleotide khc.

V d: A c thay th bng G trong si DNA. S thay th ny to ra s cp base G- T. ln sao chp tip theo to ra cp G-C trong mt phn t DNA con v cp A-T phn t DNA con kia.

Tng t, t bin thay th A bng T trn mt si, to ra s kt cp tm thi T-T. Kt qu sao chp to ra T-A trn mt phn t DNA con v A-T trn phn t DNA con kia. Trong trng hp hp ny, cp base T-A l t bin v cp A-T khng t bin. Nu si gc DNA khng t bin c trnh t 5'-GAC-3', trn si t bin c trnh t 5'-GTC-3' v si kia khng t bin c trnh t 5'-GAC-3'.

t bin thay th cp base c chia lm hai loi:

+ t bin ng hon (transition mutations): Nu mt t bin m baz pyrimidine c thay th bng mt pyrimidine v mt purine thay bng mt purine.

t bin ng hon c th l:

TC hoc CT

(Pyrimidinepyrimidine)

AG hoc GA

(purinepurine)

t bin o hon (Transversion): t bin lm thay mt pyrimidine thnh mt purine hay mt purine c thay th bng mt pyrimidine. Cc t bin o hon:

TA, TG, CA hoc CG

(Pyrimidinepurine)

AT, AC. GT hoc GC

(Purinepyrimidine)

Nh vy c th c 4 thay th kiu t bin ng hon v c n 8 thay th kiu t bin o hon. Nu cc thay th ny xy ra vi ngu nhin xc sut nh nhau, s c t l t bin: 1 ng hon : 2 o hon. Tuy nhin trong thc t, t bin thay th base c xu hng nghing v t bin ng hon, cho nn trong s cc t bin thay th base t pht th t l xy ra t bin l: 2 ng hon : 1 o hon

1.2. t bin thm hoc bt base (base-pair addition/deletion), cn gi l indel mutation (insertion-deletion). Trng hp n gin nht ca t bin ny l thm hoc mt mt cp base n. i khi t bin lm thm hoc mt ng thi nhiu cp base.

Hu qu ca t bin im n cu trc v s biu hin ca gene.

t bin im xut hin trong vng m ha chui polypeptide ca gene (a polypetide- coding part of a gene), chng hn t bin thay th base n c th gy nhiu hu qu, nhng tt c u c tc ng ln m di truyn theo 2 hng: lm thoi ha m di truyn hoc xut hin m kt thc qu trnh dch m. C cc dng:

t bin ng ngha (synonymous mutations): t bin thay i mt codon m ha acid amine thnh codon mi m ha cho cng acid amin . t bin ng ngha cng c th xem l t bin im lng (silent mutations) .t bin nhm ngha (missense mutations), i khi cn gi l t bin khng ng ngha (nonsynonymous mutations): codon m ha cho mt acid amin ny b thay i thnh codon m ha cho mt acid amin khc.t bin v ngha (nonsense mutations): codon m ha cho mt acid amin b thay i thnh codon kt thc dch m (translation termination/stop codon).

Mc nh hng ca t bin nhm ngha v v ngha ln chui polypeptide khc nhau ty trng hp.

Nu t bin nhm ngha thay th mt acid amin ny bng mt acid amin khc tng t v mt ha hc, c xem l t bin thay th bo th (conservative substitution). S thay i ny hu nh t nh hng n cu trc v chc nng protein. Ngc li, nu thay th bng mt acid amin khc v phng din ha hc gi l nonconservative substitution, hu ht u gy ra s thay i ln cu trc v chc nng protein.

t bin v ngha s dn n s kt thc dch m sm. V vy chng gy ra hu qu tng ng trn chc nng protein. Nu t bin v ngha xy ra cng gn u 3' ca khung c m, kt qu t nh hng n protein. Tuy nhin nhiu t bin v ngha vng ny vn to ra cc sn phm hon ton b mt hot tnh.Kiu t binKt qu v v d

mc DNA

ng honPurine c thay th bng mt purine khc,

pyrimidine c thay th bng mt pyrimidine

khc: AT GC, GC AT, CG TA,

TA CG

TAGC, TA AT, CG AT, CGGC

Thm/Mt

(Insertion-deletion)Thm vo hoc mt i mt hoc mt s cp base

ca DNA (thm/mt base c gch di)

AAGACTCCT AAGAGCTCCT

AAGACTCCT AAACTCCT

mc protein

t bin ng nghaCodon c bit m ho cho cng mt acid amin:

AGG CGG

Arg Arg

Loi khng bo th

Codon to thnh m ho cho amino acid khc

M ho cho acid amin c cng bn cht ho hc:

AAA AGA

Lys Arg

(kim) (kim)

M ho cho amino acid khc v bn cht ho

hc: UUU UCU

Phenylalanin Serine

K nc Phn cc

t bin v nghaCodon kt thc chui: CAG UAG

Gln Stop

t bin dch khungThm vo mt cp base:

AAG ACT CCT AAG AGC TCC T...

Mt mt cp base:

AAG ACT CCT AAA CTC CT...

Ging vi t bin v ngha, t bin thm bt base gy hu qu trn trnh t polypetide k t im b t bin (hnh 8.1). Trnh t trn mRNA c c theo tng khung gm ba base (codon) mt lc. Mt hoc thm base s lm thay i khung c trong qu trnh dch m t im b t bin cho n kt thc theo khung mi. V vy loi t bin ny c gi l t bin dch khung (frameshift mutations). t bin ny to ra trnh t acid amin k t im b t bin cho n kt thc khc vi trnh t acid amin gc. t bin dch khung gy ra s mt hon ton cu trc v chc nng ca protein bnh thng.

Trng hp t bin xy ra trnh t iu ha v cc trnh t khng m ha khc. hng phn ca gene khng trc tip m ha cho protein m cha nhiu im bm DNA ch yu cho protein xen vo, l nhng trnh t khng nhy cm cho s biu hin ca gene hoc cho hot tnh ca gene.

mc DNA, nhng im mt i (docking) gm nhng im m RNA polymerase v nhng nhn t gn kt ca n bm vo, cng nh nhng im m protein iu ha phin m c trng gn vo. mc RNA, nhng docking quan trng thm vo gm im bm ca ribosom (ribosome-binding site) trn mRNA vi khun, nhng im ni u 5' v 3' gn cc exon eukaryote v cc im c vai tr cho iu ha dch m v nh v mRNA n vng c bit trong t bo. Nhn chung hu qu chc nng ca bt k t bin im no vng nh th u ph thuc vo vic lm gin on (hoc to ra) mt im bm. t bin lm gin on nhng im c kh nng lm thay i phn biu hin ca gene da vo s thay i s lng sn phm c biu hin mt thi im nht nh hoc mt m nht nh. hay bng s thay i phn ng vi nhng tn hiu (cue) ca mi trng nht nh. Ngc li, t bin

mt vi im bm c th hon ton ph hy mt giai on cn cho s biu hin bnh thng ca gene, nh im bm ca mRNA polymerase hoc l nhn t splicing. V vy n lm bt hot sn phm ca gene hoc ngn cn s hnh thnh sn phm.

Cn phn bit gia nhng thay i xy ra ca mt t bin gene l s thay i trnh t DNA ca gene vi s thay i mc kiu hnh. Nhiu t bin im trong trinh t khng m ha lm t thay i hoc khng thay i trn kiu hnh nh t bin gia im bm DNA cho protein iu ha hoc thay i nhng im khc trong gene lm thay i chc nng ca chng.

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