Biocel Curs Nucleul
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Transcript of Biocel Curs Nucleul
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NUCLEUL II
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CROMATINA
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CROMATINA/clasificare
• EUCROMATINA• Palid colorata, cu
cromozomi decondensati,
• fibra cromatidiana despiralizata/nespiralizata.
• activa genetic, AND in replicare , transciere
• HETEROCROMATINA• Intens colorata,
segmente de cromozomi ramin condesati
• AND inactiv- nu transcriptie
• CONSTITUTIVA, FACULTATIVA
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EUCROMATINA Funcţie: TRANSCRIPŢIE (ARNm,ARNt,ARNr5s) Enzime
implicate:ARN polimeraze II, III Produs: ARNm,t,r 5s
Exoni = fragmente nucleotide ADN trancrise pe ARN Introni = secvenţe ce separă exonii Maturare ARNm- excizia introni-exoni uniţi cap la cap maturare transcript primar( ARNpre m, ARNheterogen m) (metilare,acetilare,fosforilare, complexare cu proteine) →POR Informozomi = ARNm + Proteine ME: granule inter / pericromatidiene
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Clasificarea eucromatina /heterocromatina, apartine germanului Heitz inca din 1927. Poate fi transpusa si prin faptul ca eucromatina este accesibila ARN polimerazei II, iar heterocromatina nu permite acest acces.
Raportul eucromatina /heterocromatina , care functional se traduce pin raportul transcriptibil/netranscriptibil, perimite elucidarea dilemei citogenetice genotip//fenotip!!
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Genotipul - totalitatea materialului genetic reprezentat de cromatina interfazica( eucromatina si heterocromatina)
Fenotipul , ca expresie a genotipului este complexul de trasaturi exprimate din genotip, respectiv ceea ce se transcrie din eucromatina.
Numai transcriptibilitatea materialului genetic activ ( eucromatina)este supusa reglarii ; nu si structura .
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HETEROCROMATINA CONSTITUTIVA
Permanent condensată Inactivă genetic (niciodată transcrisa)
Mai ales la nivelul cromozomilor 1,9,16,YFormată din ADN (1/3 inalt-, 2/3 mediu- repetitiv)
pericentromeric (ADN satelit),constricţii secundare
Cantitate variabilă funcţie de specieReplicată tardiv in S Explică paradoxul valorii C
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• Valoarea C = cantitatea de ADN(picograme) din nucleul haploid al unei specii (C)
• Cel.diploide au 2C• Ar trebui sa crească cu complexitatea organisme
• Dar animale inferioare au C > mamifere *salamandra-168pg *om - 6pg
• Au mai mult ADN neinformaţional !
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• Cantitatea ADN – Număr cromozomi → EVOLUŢIA SPECIILOR ?
• SALAMANDRA: 168 pg ADN si detine recordul lungimii moleculei de ADN de :2,5m!.
• CROMOZOMI• Albina 32, Feriga 1262, Găina 78, Câine 78,
Cal 64 • Om 46 !!!!!
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HETROCROMATINA FACULTATIVA AUTOSOMALA
• Segmente hipercondensate cromozomi autosomi mărimea si distribuţia heterocromatinei se modifică funcţie de ce segmente urmează să fie transcrise
• Are sens genetic – gene au fost / urmează transcrise• Gene inactive / represate• Cantitatea / distribuţia →activitatea / specializarea cel.• Se poate converti in eucromatină• Celule degenerate→picnoză
(eucromatina→heterocromatina)• Diferenţiere celulară- genele represate diferă
de la un tip de celulă la altul
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HETEROCROMATINA FACULTATIVA GONOZOMALA
• Inactivă pe toata durata ciclului celular• Cromatina SEXUALĂ• CORPUSCUL BARR (Cromatina X)
(inactivarea aleatorie a un Cr. X – z 14 embrion) Mary Lion (lionizare)
sferic/oval ataşat de MNI, de nucleol, “drum stick” marker citologic genetic de sex feminin la mamifere femeia “mozaic genetic”→celule cu X(tata),X(mama)
• CORPUSCUL F (Cromatina Y) braţul Cr.Y inactiv genetic, bogat in A-T Fluorescenţa cu Quinacrină marker genetic de sex masculin (om, gorila)
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HETEROCROMATINA
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DOGMA CENTRALA A BIOLOGIEI MOLECULARE
• ADN- singurul depozitar al informatiei genetice
• ADN- se autoreplica • ADN- constituie matrita pentru sinteza ARNm• ARNm – constituie matrita pentru sinteza
lantului polipeptidic specific
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DOGMA – FLUXUL INFORMATIEI GENETICE
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• Au descifrat structura AND-lui dublu spiralat, dublu catenar, aducind lumina in descifrarea singurului detinator al informatiei genetice
• O celua somatica diploida contine cca. 6,5 ngr de AND. Cantitatea de AND din nucleu este proportionala cu necesarul de informatie genetica si este specifica fiecarei specii.
• Cantitatea de 6,5pg de AND, din celulele somatice diploide este constanta si se dubleaza prin autoreplicare inainte de perioada S , respectiv in faza G1
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Gradele de condensare ale cromatinei , caracteristice pentru cromozomi in metafaza
• Str elicoidala a mol de AND
• Asocierea AND-lui cu histone si formarea nucleozomilor
• Cresterea gradului de condensare
• Cromozom in metafaza
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BANDARE CROMOZOMIALA SI IMPORTANTA EI
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• Bandarea cromozomilor prin tehnici diverse, are o importanta deosebita in practica medicala:
• Diagnosticul bolilor congenitale la nou-nascuti
• Sfatul genetic si prognoza genetica• Aprecierea statusului fetal pentru familiile cu
risc genetic mare• Diagnosticul diferential al anomaliilor
sexuale, a un unor boli de singe, al tumorilor benigne si maligne
• Expertiza medico-legala
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NUCLEOLUL
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NUCLEOLUL• Corpuscul intranuclear, interfazic, vital • Rol: biogeneza ribozomi • Control ciclu celular / diviziune celulară • In absenţa lui nu se sintetizează proteine/nu diviziune • Dimensiuni: 0,5 – 2 μm (> celule sinteză ↑ proteine)• Forma: rotund – oval Nu inveliş (Nucleolonema)
• Localizare: central / excentric (poate varia funcţional) • Număr: 1 – 10 (medie 2 – unul /set haploid) in toate celulele! • Vizibil / nu – frecvent in afara planului de secţiune• Compoziţie chimică (dupa digestie enzimatică):
ADN 3% (ADNaza) ARN 7% (ARNaza) Proteine 90% (proteaze)
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BAZOFIL/ nucleu eucromatic( heterocromatic greu)
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ARN/ col Brachet ( verde metil pironina)
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AND asociat / coloratie Feulgen-AND rosu-violet
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ME : Structura nucleolPars FIBROSA – reţea filamente ARN Pars GRANULOSA (dominantă) granule preribozomiPars CROMOSOMA – periferie/ interior ADN Pars AMORPHA – omogenă proteine
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• Corelaţie STRUCTURĂ – FUNCŢIE
studierea incorporării Uridinei marcată radioactiv
Pars Chromosoma → Fibrosa → Granulosa → →ribozomi citoplasmatici
Concluzie: Biogeneza ribozomilor
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BIOGENEZA RIBOZOMILOR• Nucleolul conţine bucle de ADN
– 5 perechi Cromozomi (13, 14, 15, 21, 22) x 2 = NOR 2 NOR (Nucleolar Organizing Center)
• ADNr transcripţie (ARNpolimeraza I)→ ARNr 45s Maturare: ARNr 45s→ 41s→32s→28s + 5,8s + 5s + 45
proteine →Particula 60s (1oră) ( ARNr5s -Cr 1 extranucleolar, ARNpolimeraza III )
ARNr 45s→ 41s→21s→18s + 38 proteine
→Particula 40s (30 min)
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• In momentul declanşării diviziunii celulare,(profaza) – Nucleolul se micşorează→dispare
• in mitoză sinteza ARN stopată ARNpolim/ADNpolimeraza – asociate NOR (telofaza) – reconstrucţie prin interacţiunea 10 corpi prenucleolari (proteine specifice) cu NOR → fuzionează → 2 nucleoli
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3 REGIUNI NUCLEOLARE
• Centrul Fibrilar (mai clar) conţine proteine implicate in transcriere -ARN polimeraza I, ADN polimeraza I factori de transcriere. nucleolina-navetă Nucleu-Citoplasmă transcriere ADNr→ARNr45s fosforilată- eliberează histonele H1→transcriere defosforilată- leagă H1→ inhibă transcrierea
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• Component Fibrilar Dens (densă in jur centru fibrilar) conţine proteine implicate in clivajul preARNr si asamblarea post-transcripţie a preribozomi
• Componenta Granulară
(inconjoară precedenta) conţine preribozomi
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MATRICEA CELULARA
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• Ordoneaza enzimele de replicare,transcriere ARNpolimerazele - fixate de reţeaua fibrilară (rămân imobile – molec. ADN se deplasează)
• Schelet de fixare a cromozomilor in locuri bine definite
• ADN – centromerele-contact cu nucleolul telomerele – inseră pe lamina nucleara,MNI bucle-extremitatea se asociază cu reţeaua
• Organizează nucleolul• Rol in mitoză – reconstrucţia nucleară
(proteine Nu MA -aparat mitotic nuclear)
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• Materialul insolubil care persistă in urma: extragere proteine + lipide (detergenţi) digestie enzimatică (ADNaza, ARNaza) extragere proteine (soluţii saline)
• Reţea de fibre de 3-5nm in care sunt inglobate granule >25nm
• Compoziţie chimică: proteine 85-95% ADN,ARN ~15%, lipide ~ 1%
• 30 tipuri proteine : lamine , actina, etc.
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DIVIZIUNE CELULARA
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• REPREZINTA FORMAREA DINTR-O CELULA A DOUA CELULE FICE , PRIN DIVIZIUNE DIRECTA ( CA MITOZA) SI PRIN DIVIZIUNE INDIRECTA ( MITOZA SI MEIOZA)
• MITOZA• Profaza, metafaza , anafaza,si telofaza
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FAZE ALE MITOZEI
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CICLUL CELULAR
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MULTUMESCDr. Alina Draghia