membranele celulare
TRANSCRIPT
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Membrana plasmatica
Definitie: Separa mediul intracelular de mediul extracelular
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Rolul membranei celulare Bariera-permeabilitate selectiva Transferul de informatie Analiza informatiei Inhibitie de contact Recunoasterea celulara Metabolismul celular Fixarea de virusuri sau toxine
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Compozitia biochimica: Membrane cu rol de bariera L P
(mielina)
Membrana cu rol de bariera si functie enzimatica L=P Membrana plasmatica
Membrane cu functie metabolica P (75%) L (25%)
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Tipuri de membranelor
6-10 nm6 nm
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Fosfolipidele
C
C
C
H
H2
H2
HO
HO
HO
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Fosfolipidele
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Sfingomielina
1. Derivat de un alcool aminat (sfingozina)2. Acid gras
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Fosfogliceride(PC) / Sfingolipide (SM)
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Glicolipidele
Regiune hidrofoba ce contine doua cozi lungi hidrocarbonate
O regiune polara ce contine una sau mai multe rezidii glucidice fara fosfat
Glucidele: glucoza, fructoza, glucosamina.
Prezinta sarcini negative datorita licacidului sialic
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Colesterol
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Colesterolul
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Localizarea proteinelor in membrana
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Modelul de membrana Gorter şi Grendel .
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Modelul de membrana Danielli Davson modificat de Robertson
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Mozaicul fluid lipidoproteic - Zinger
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Asimetria fosfolipidelor
fosfatidilcolina sfingomielina fosfatidilserina
fosfatidilinozitol fosfatidiletanolamina
e
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Mobilitatea fosfolipidelor
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virus Sendai
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Suprafata celulara
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Glicocalixul sau glicolema
Caracterizat prin prezenta pe suprafata celulara de glicoproteine si glicolipide
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Funcţiile glicocalixului adezivitatea intercelulară depozit de cationi legaţi de acidul sialic Asigura identitatea celulei prin antigenele celulare
(antigenele de grup sanguin din membrana hematiei) recunoaşterea celulară; procesele de semnalizare celulară; procesele de apărare ale organismului, în imunitate.
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Joncţiunile celulare
Joncţiuni de adezivitate: desmosomii
Joncţiuni impermeabile: joncţiunile strânse.
Joncţiunile de comunicare: joncţiunile permeabile şi sinapsele
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Desmosomii în centură
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Desmosomii în „pată”
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Desmosomii în „pată”
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Hemidezmosomi
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Joncţiuni impermeabile: joncţiunile
strânse
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Joncţiuni impermeabile: joncţiunile strânse
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Joncţiunile de comunicare
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Joncţiunile de comunicare
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1.Receptorii - definitie proteine cu funcţii de legare specifică şi cu
afinitate mare pentru liganzi.
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Localizarea receptorilor
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Liganzii molecule cu rol de semnal exogene :
Virusuri Bacterii toxine bacteriene medicamente
endogene: mediatori chimici locali hormoni neurotransmiţători.
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ligant + receptor raspuns celular
Redistribuirea receptorilor din membrana
Activarea unor enzime din plasmalema
Captarea lor in vezicule de endocitoza
Modificari de permeabilitate membranara
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cAMP AMPfosfodiesteraza
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Conditii patologice
Toxina vibrionului holeric
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Na + traverseaza mucoasa
transport de apa
ireversibil
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cAMP
protein kinaze
diferite enzime
Mesager de ordinul 2
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Sinteza de glucoza
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Hormonii hidrosolubili
Mitogen Activated Protein
gene regulatory protein
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In celulele specializate
• AMPc determina sinteza de: – glucocorticoizilor în medulosuprarenală sub
acţiunea ACTH – progesteronului în corpul galben sub acţiunea
hormonului luteal (LH) – activarea transportului calciului în corticala
rinichiului sub acţiunea parathormonului
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Hormonii liposolubili
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Creşterea concentraţiei intracelulare a Ca2+
deschiderea unor canale din
plasmalemă
deschiderea unor canale din : muşchi din reticulul
sarcoplasmic
Ca2+ - calmodulina
+ calmodulina
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Ca2+ - calmoduline
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Ca2+ - calmoduline
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Ca2+ - calmodulina
fosfodiesteraza fosfodiesteraza *
adenilatciclaza adenilatciclaza *
kinaza kinaza *
Ca2+- ATPase Ca2+- ATPase*
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Transportul
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Difuziunea simplasubstanţele liposolubile trec prin membrană cu o viteză proporţională cu coeficientul lor de partiţie între lipide şi apă
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Transportul ionilor prin ionofori
Na
K
Filipina
Nistatina
Amfotericina B
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Difuziunea facilitata
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Difuziunea mediată de proteinele canal
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Difuziunea mediată de proteinele canal
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Transportul apei prin membrane
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Transportul activENERGIE
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Pompe ionice
Pompa de protoni in membrana
lisosomi bacteri
Pompa Na+ K+ membrana citoplasmatica a celulei eucariote
Pompa H+ K+ Membrana celulelor gastrice regiunea apicala
Pompa de Ca+
membrana celulelor eucariote Membrana reticulului sarcoplasmic
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Pompa de H+
Pompa din clasa V are doua regiuni:
V1 – hidrofila si V0 – transmebranara
ATP se ataseaza de subunitatea B localizata in V1
Canalul de protoni este format din subunitatea C si A localizata in V0
V1
V0
ATP
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Pompa de protoni H+
mecanism
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K
Na
K
Na+ 50 mM
K+ 400mM
Na+ 440 mM
K+ 20 mM
_
_++ +++_
_+ Potential de membrana –20 mV şi –200 mV
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Pompa Na+ K+
Structura:
Patru polipeptide transmembranare.
Doua polipeptide mari formeaza subunitatea .
doua polipeptide mici formeaza subunitatea .
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Pompa Na+ K+ mecanism
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Transportul activ cuplat cu gradiente ionice
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Concentraia de Ca in celula
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Ca2+
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Ca2+-ATPPompa din clasa P are doua
regiuni: Transmebranara formata din
10 α hélix ce contine un sit de fixare a Ca2+
Un segment citosolic cu trei locuri de
legare a nucleotidului fosforilare activare
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Transportul de Ca2+
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Ca2+-ATP mecanism
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P 170 MDRP (Multiple Drug Rezistance Protein)
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Transportul prin vezicule
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Fagocitoza
• la protozoare - modalitate de hrănire.• la mamifere şi la om - rol important în
procesele de apărare ale organismului • celulele capabile de fagocitoză – fagocite
– In sange• macrofage - monocite• leucocitele - polimorfonucleare cu granulaţii
neutrofile
– macrofagele – in tesut se numesc histiocite
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Funcţia fagocitelor
• îndepărtare a celulelor bătrâne
• distrugere a microbilor
• îndepărtează şi celulele:– moarte– maligne
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1. Etapele fagocitozei Chemotactismul - mişcarea dirijată a fagocitelor
spre locul infecţiei componente bacteriene (proteine sau lipide) componente din organism:
proteine serice kalicreina componentele sistemului numit complement
produse de limfocite limfokine
de neutrofile componente din celulele moarte
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2. Etapele fagocitozei Recunoaşterea şi ataşarea fagocitelor de particule se
face prin receptori din plasmalema fagocitului ce recunosc liganzi de pe suprafaţa particulei.
Indepartarea acidul sialic de pe membrana eritrocitelor determina fagocitarea acestora in splină
Celulele maligne au foarte puţin acid sialic pe suprafaţa lor şi de aceea sunt distruse
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3. Etapele fagocitozei Înglobarea: se face prin emiterea de către
fagocit a unor prelungiri numite pseudopode
Omorârea celulelor fagocitate şi digerarea lor: se face după fuziunea fagosomului cu endosomii tardivi şi cu lisosomii
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Distrugerea celulelor fagcitate
oxidaza din plasmalemă
2O2 + NADPH → 2O2- + NADP- + H+
Din recţia O2- + H2O2
hidroxil (OH) oxigenul singlet (1O2)
specii foarte reactive şi toxice care omoară microbii
catalizeaza
convertit
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Endocitoza
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LDL- “Low-density lipoproteins”
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Endocitoza dependenta de receptori
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CH
+ Lp
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Exocitoza
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Exocitoza - exemple evacuarea produşilor de secreţie celulară evacuarea neurotransmiţătorilor în spaţiul sinaptic; evacuarea granulelor de melanină din melanocitele
din piele Evacuarea resturilor nedigerabile din veziculele
lisosomale - defecare celulară evacuarea enzimelor lisosomale în condiţii:
fiziologice - de pildă din osteoclaste Patologice:
regurgitare celulară starea de şoc
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1.Implicaţiile membranelor în patologie
Boli genetice datorate defecte de membrană localizate la un singur tip de
celulă anemii microcitare
sferocitoza eliptocitoza
defecte de membrană cu caracter generalizat distrofiile musculare
distrofina
canalopatiile, în care sunt modificate ca structură unul dintre canalele ionice epilepsi genetice
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2. Implicaţiile membranelor în patologie Boli genetice ale organitelor celulare
lipsa unei proteine modificarea structurii unei proteine de membrană
Implicarea membranelor în bolile autoimune Cauzate de modificarea structurii proteinelor sau a
lipidelor din membrane Rezultatul este că celulele sunt recunoscute ca străine de către
organism - rezultand anticorpi.
Anticorpi atacă toate celulele de un anumit tip, rezultând boli autoimune: anemii, hepatite
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3. Implicaţiile membranelor în patologie In bolile cardiovasculare
In hipertensiunea arterială - canalelor ionice In ateromatoză
implicaţii ale membranelor defectul receptorilor pentru LDL
Membranelor în cancer modificări ale:
plasmalemei unor membrane intracelulare (de pildă ale aparatului Golgi)