Exocitosis. Figure 13-66a Molecular Biology of the Cell (© Garland Science 2008)
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Transcript of Exocitosis. Figure 13-66a Molecular Biology of the Cell (© Garland Science 2008)
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Exocitosis
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Figure 13-66a Molecular Biology of the Cell (© Garland Science 2008)
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Page 799 Molecular Biology of the Cell (© Garland Science 2008)
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Vías de secreción:
• Vía constitutiva: contínua, todas las células.
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Figure 13-64 Molecular Biology of the Cell (© Garland Science 2008)
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Figure 13-63 Molecular Biology of the Cell (© Garland Science 2008)
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Figure 13-65a Molecular Biology of the Cell (© Garland Science 2008)
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Figure 13-65b Molecular Biology of the Cell (© Garland Science 2008)
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Figure 13-66b Molecular Biology of the Cell (© Garland Science 2008)
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Figure 13-67 Molecular Biology of the Cell (© Garland Science 2008)
Procesamiento Proteolítico: pre-pro-proteínas
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Vesículas de secreción:
requieren señal de membrana (unión mensajero-receptor, potencial eléctrico) para liberar contenido al exterior.
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Exocitosis en las células nerviosas
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Figure 13-68 Molecular Biology of the Cell (© Garland Science 2008)
Exocitosis puede ser un proceso global…
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Figure 13-69 Molecular Biology of the Cell (© Garland Science 2008)
… o localizado.
Exocitosis de un mastocitoen una región limitada.
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Figure 13-1 Molecular Biology of the Cell (© Garland Science 2008)
El ciclo exocitosis-endocitosis mantiene el área de membrana constante
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Figure 13-70 Molecular Biology of the Cell (© Garland Science 2008)
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Figure 13-71 Molecular Biology of the Cell (© Garland Science 2008)
Ejemplos de células polarizadas
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Figure 12-56 Molecular Biology of the Cell (© Garland Science 2008)
Anclaje glicosilfosfatidilinositol (GPI)
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Balsas lipídicas (lipid rafts)
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Figure 13-72a Molecular Biology of the Cell (© Garland Science 2008)
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Figure 13-72b Molecular Biology of the Cell (© Garland Science 2008)
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Figure 13-73 Molecular Biology of the Cell (© Garland Science 2008)
Vesículas sinápticas en la neurona
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Citoesqueleto
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Figure 16-1 Molecular Biology of the Cell (© Garland Science 2008)
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• Determina la forma y proporciona soporte estructural.
• Permite las funciones mecánicas de la célula(crecimiento, movimiento, división).
• Determina la posición de orgánulos y dirige el transporte intracelular.
• Proporciona resistencia frente a estrés mecánico.
El citoesqueleto:
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Figure 16-2 Molecular Biology of the Cell (© Garland Science 2008)
Cambios de conformaciónasociados a la división celular
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Componentes del citoesqueleto:
• Microfilamentos (actina)
• Microtúbulos
• Filamentos intermedios
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MICROFILAMENTOS(filamentos de actina)
• Polímeros de actina en trenza.
• Se concentran bajo la membrana (córtex).
• Determinan la forma celular yson esenciales para la locomoción.
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MICROTÚBULOS
• Cilindro hueco de tubulina.
• Un extremo se une al centrosomao recorre célula de una lado a otro.
• Posición orgánulos y transporteintracelular.
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FILAMENTOSINTERMEDIOS
• “Cuerdas” de fibras heterogéneas.
• Anclaje entre células, lámina nuclear...
• Fuerza y resistencia al estrés mecánico.
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Figure 16-5 Molecular Biology of the Cell (© Garland Science 2008)
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Cómo son las uniones en el citoesqueleto?
Se trata de uniones NO COVALENTES que permiten
el ensamblaje y desensamblaje RAPIDOS.
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Polimerización de componentes del citoesqueleto
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Figure 16-7 Molecular Biology of the Cell (© Garland Science 2008)
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CONCEPTOS (I)
NUCLEACIÓN. Etapa inicial en la formación de un filamento:
Oligómero corto (inestable) – Estabilización(*) – Rápida polimerización
(*) estabilización a partir de un determinado tamaño.
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CONCEPTOS (II)
POLARIDAD D FILAMENTOS. Los dos extremos de unmicrotúbulo o un filamento de actina son distintos:
Extremo de crecimiento rápido (+) – crecimiento lento (– )
+-
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CONCEPTOS (III)
ACTIVIDAD ATPasa/GTPasa:
• Filamentos de ACTINA: ATPasa
• MICROTÚBULOS: GTPasa
Los monómeros libres también tienen esta actividad, aunque menor.
Hidrólisis de ATP/GTP
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CONCEPTOS (IV)
ENSAMBLAJE Y DESENSAMBLAJE:
Los filamentos de actina y los microtúbulos unen y pierdenunidades por sus extremos.
El extremo + crece más rápidamente que el extremo –.
+-
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CONCEPTOS (V)
RECAMBIO ROTATORIO (TREADMILLING):
La adición de subunidades tiene lugar más rápidamente que la hidrólisis de ATP/GTP.
Ensamblaje en extremo + y desensamblaje en extremo –.
+-
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CONCEPTOS (VI)
INESTABILIDAD DINÁMICA (microtúbulos):
Etapas alternantes de crecimiento y rotura en un extremo.
(la despolimerización tiene lugar más rápidamente en un extremo GDP que en un extremo GTP).
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Conservación evolutiva de los filamentos:
• Actina, tubulina: gran conservación evolutiva.
• Filamentos intermedios: hay variedad…
Ej: filamentos queratina (céls epiteliales)neurofilamentos (fibras nerviosas)filamentos de desmina (fibras musculares)
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Sustancias que alteran la polimerización
(toxinas naturales producidas por plantas, hongos y esponjas como mecanismo de defensa)
• Latrunculina (esponja): despolimeriza actina
• Faloidina (hongo): estabiliza y polimeriza actina
• Colchicina (del azafrán): despolimeriza microtúbulos
• Taxol (corteza de un árbol): polimeriza microtúbulos
Todas son substancias CITOTÓXICAS(el taxol se usa para destruir células tumorales)