Download - Mitose+ Meiose.ppt
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La mitose est une division binaire qui permet la multiplication cellulaire enAssurant: -la croissance de l’ organisme -le renouvellement des cellules de l’adulte et - la restauration cellulaire.
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Stade de segmentation
Embryon de deux mois
Croissance de l’organisme.(jusqu’à l‘âge adulte)
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Renouvellement des cellules de l’adulte.
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CDK cyclines G1
MPF
MPF=facteur promoteur de la mitose.
Le cycle cellulaireLe cycle cellulaire.
Cellule intermitotique.
Cellule postmitotique.
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Les caractéristiques des phases de l’interphase:-Phase G1: - G1 =0: cellules embryonnaires. - G1 augmente progressivement:le cas de la différenciation.
-Phase G2: - G2=0 : cellules embryonnaires. - Cellules bloquées en G2 : cellules de l’épiderme.
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Deux familles de protéines clés: - Les protéines kinases cyclines dépendantes(CDK) - les cyclines (protéines activatrices).
CONTRÔLE DU CYCLE CELLULAIRE
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Evolution de la quantité d’ADN au coursEvolution de la quantité d’ADN au coursDu cycle cellulaire.Du cycle cellulaire.
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La mitose est formée de 5 phases successives:
La prophase;La prémétaphase;La métaphase;L’anaphase etLa télophase.
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Prophase
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Matériel centriolaire
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Matériel centriolaireCondensation chromosomique
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Prémétaphase.
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Phase G2Phase G2
Métaphase.
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INTERZONE}
Métaphase.
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METAPHASE
Fuseau achromatiqueKinétochoresMicrotubules du
Chromosomes
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Le déclenchement de l’anaphase a une double origine: la dégradation de la cycline mitotique , l’ augmentation brûtale de la concentration cytosolique des ions Ca+.
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Rôle des kinétochores dans Rôle des kinétochores dans la mobilité des la mobilité des chromosomeschromosomes
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La télophase.
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Prophase
Métaphase
Anaphase
Télophase
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L’ étude des mécanismes d’élaboration et de séparation des chromosomes dans la mitose nous a montré que la mitose répondait à une loi de conservation qualitative et quantitative de l’information génétique , qui est maintenue stable sous une forme diploïde (2n).
La méiose correspond à un mécanisme de réduction de ploïdie( 2n n ) ,et c’est le phénomène indispensable et préalable à la Fécondation qui permet le retour à la diploïdie( n’ +n’’ 2n ).
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La méiose correspond à l’enchaînement de deux divisions binaires successives : _la mitose réductionnelle précédée d’une phase S , _la mitose équationnelle qui succède immédiatement à la première sans interphase (G1+ S + G2 ).
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Anaph.I
Anaph.II
( gamètes )
(G1)
(S)
(G2)
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(G1)
(S)
(G2)
Gamètes
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LES ETAPES DE LA MEIOSE.La mitoseréductionnelle: précédée d’une phase S
Prophase I: 6 stades:
LEPTOTENE ;SYNAPTENE;ZYGOTENE;PACHYTENE;DIPLOTENE;DIACINESE.
Métaphase IAnaphase I Télophase ILa mitose équationnelle: sans phase S.
Prophase IIMétaphase IIAnaphase IITélophase II
I-
II-
Mitose réductionnelle = 1e mitose de maturation.Mitose équationnelle = 2e mitose de maturation.
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Stade leptotène( leptos=mince)
Plaques D’ adhérence
M O = chrom.Non dupliqués.
M E =Dupliqués S.
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Stade synaptène:Début de formation du complexe synaptonémal
2 chrom.homologues
Rapprochement
( synapsis = lien)
( pour toutesLes paires )
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}Stade Leptotène.
}Stade synapténe
Elément centralDevient latéral.
AppaChrom.homol.
_1e~300nm
_2e~ 100nm
( maternelles)
( paternelles)
riement
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Le complexe synaptonémal.
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Le complexe synaptonémal.Le complexe synaptonémal.
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Stade zygotène:
Achèvement de la formation du complexe synaptonémal.
centromères
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Stade pachytène
Chromosomes courts et épais ; brassage interchromosomique.
Nodules de recombinaisons
( pachy=épais)
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Brassage interchromosomique.
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Stade diplotèneDissociation du C.S. à partir des centromères (chromatides liées
par les chiasmas.
( diplos =double)
•Ovocytes I Ovocytes I Bloqués à Bloqués à Ce stade .Ce stade .
Ecartementdes Centromères.
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Stade de diacinèse:Dissociation de l’enveloppe nucléaire.
_Chromatides recombinées unies par les centromères. Chromatides homologues liées par les chiasmas.
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TELOPHASE I:_Chaque cellule hérite N diades (N = 23 )
_Fuseau achromatique disparaît.
_Enveloppe nucléaire se reforme.
_Cytodiérèse ( selon les lignées ).
LA MITOSE EQUATIONNELLE:
_Elle succède à la précédente (débit variable gamètes mâles ou femelles).
_Elle se déroule comme une mitose normale mais sans phase S.
PROPHASE II
_Elle est très courte car les diades sont déjà condensées._ Elle se confond avec la télophase I.
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La télophase II avec cytodièrèse:
On obtient 4 gamètes c a d : _ 4 spermatozoïdes chez l’ homme et _ 1 ovocyte II + 2 ou 3 globules polaires chez la femme.
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Synapsis des chromosomes sexuels au niveau des régions pseudo-
Autosomique. : environ 1/10 de l’ Y. ( Un seul chiasma peut se former)
Conséquences
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La diversification de l’ espèce humaine s’explique par la diversification des gamètes mâles et femelles grâce au crossing over et à La ségrégation aléatoire .
( Métaph.I et métaph.II)
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Rôle des phosphatases et des Rôle des phosphatases et des kinases pour le développement kinases pour le développement harmonieux des microtubules.harmonieux des microtubules.
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Diplosome
Microtubules astériens
Microtubules
hémipolaires
Asters
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Le complexe Cycline / Cdk agit en phosphorylant une protéine
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Metaphase
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SY
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Pendant que l'être humain se développe pour atteindre l'âge Pendant que l'être humain se développe pour atteindre l'âge adulte, les adulte, les
Croissance de l’organisme.
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