Desarrollo y patrones arquitectónicos
Dr. Robert J. Mayer
UPR en Aguadilla
Presentación 2
http://math.uprag.edu/rmayer/zoopres2.ppt
Tareas
Leer hasta la página del libro de Carl Safina
Escribir una biografía corta del autor y entregarla el 1.24.11
Leer los capítulos 8 y 9 del libro de texto “Zoology”
Objetivos
Conocer los conceptos básicos de la biología del desarrollo
Conocer los conceptos básicos de la embriología
Phases of the Cell Cycle• The cell cycle consists of
– The mitotic phase– Interphase INTERPHASE
G1
S(DNA synthesis)
G2Cyto
kines
is
Mito
sis
MITOTIC(M) PHASE
Figure 12.5
• Mitosis consists of five distinct phases– Prophase– Prometaphase
G2 OF INTERPHASE
PROPHASE PROMETAPHASE
Centrosomes(with centriole pairs) Chromatin
(duplicated)
Early mitoticspindle
Aster
CentromereFragmentsof nuclearenvelope
Kinetochore
Nucleolus Nuclearenvelope
Plasmamembrane
Chromosome, consistingof two sister chromatids
Kinetochore microtubule Figure 12.6
Nonkinetochoremicrotubules
G2 of Interphase• A nuclear envelope bounds the nucleus.• The nucleus contains one or more nucleoli (singular, nucleolus).• Two centrosomes have formed by replication of a single centrosome.• In animal cells, each centrosome features two centrioles.• Chromosomes, duplicated during S phase, cannot be seen individually because they have not yet condensed.
The light micrographs show dividing lung cells from a newt, which has 22 chromosomes in its somatic cells (chromosomes appear blue, microtubules green, intermediate filaments red). For simplicity, the drawings show only four chromosomes.
PROPHASE PROMETAPHASE
Chromatin(duplicated)
Early mitoticspindle
Aster
CentromereFragmentsof nuclearenvelope
Kinetochore
Plasmamembrane
Chromosome, consistingof two sister chromatids
Kinetochore microtubule
Nonkinetochoremicrotubules
Prophase• The chromatin fibers become more tightly coiled, condensing into discrete chromosomes observable with a light microscope.• The nucleoli disappear.• Each duplicated chromosome appears as two identical sister chromatids joined together.• The mitotic spindle begins to form. It is composed of the centrosomes and the microtubules that extend from them. The radial arrays of shorter microtubules that extend from the centrosomes are called asters (“stars”).• The centrosomes move away from each other, apparently propelled by the lengthening microtubules between them.
Prometaphase• The nuclear envelope fragments.• The microtubules of the spindle can now invade the nuclear area and interact with the chromosomes, which have become even more condensed.• Microtubules extend from each centrosome toward the middle of the cell.• Each of the two chromatids
of a chromosome now has a kinetochore, a specialized protein structure located at the centromere.• Some of the microtubules attach to the kinetochores, becoming “kinetochore microtubules.” These kinetochore microtubules jerk the chromosomes back
and forth.• Nonkinetochore microtubules interact with those from the opposite pole of the spindle.
PROMETAPHASE
CentromereFragmentsof nuclearenvelope
Kinetochore
Kinetochore microtubule
Nonkinetochoremicrotubules
METAPHASE
Spindle
Metaphaseplate
Centrosome at one spindle pole
Daughter chromosomes
Metaphase• Metaphase is the longest stage of mitosis, lasting about 20 minutes.• The centrosomes are now at opposite ends of the cell. •The chromosomes convene on the metaphase plate, an imaginary plane that is equidistant between the spindle’s two poles. The chromosomes’ centromeres lie on the metaphase plate. • For each chromosome, the kinetochores of the sister chromatids are attached to kinetochore microtubules coming from opposite poles. • The entire apparatus of microtubules is called the spindle because of its shape.
METAPHASE ANAPHASE TELOPHASE AND CYTOKINESIS
Spindle
Metaphaseplate Cleavage
furrow
Nuclear envelopeformingCentrosome at
one spindle poleDaughter chromosomes
Anaphase• Anaphase is the shortest stage of mitosis, lasting only a few minutes.• Anaphase begins when the two sister chromatids of each pair suddenly part. Each chromatid thus becomes a full- fledged chromosome.• The two liberated chromosomes begin moving toward opposite ends of the cell,
as their kinetochore microtubules shorten. Because these microtubules are attached at the centromere region, the chromosomes move centromere first (at about 1 µm/min).• The cell elongates as the nonkinetochore microtubules lengthen.• By the end of anaphase, the two ends of
the cell have equivalent—and complete—collections of chromosomes.
Telophase• Two daughter nuclei begin to form in the cell.• Nuclear envelopes arise from the fragments of the parent cell’s nuclear envelope and other portions of the endomembrane system.• The chromosomes become less condensed.• Mitosis, the division of one nucleus into two genetically identical nuclei, is now complete.
Cytokinesis• The division of the cytoplasm is usually well underway by late telophase, so the two daughter cells appear shortly after the end of mitosis.• In animal cells, cytokinesis involves the formation of a cleavage furrow, which pinches the cell in two.
TELOPHASE AND CYTOKINESIS
Nucleolusforming
Cleavagefurrow
Nuclear envelopeforming
– Metaphase– Anaphase– Telophase
Centrosome at one spindle pole
Daughter chromosomes
METAPHASE ANAPHASE TELOPHASE AND CYTOKINESIS
Spindle
Metaphaseplate Nucleolus
forming
Cleavagefurrow
Nuclear envelopeforming
Figure 12.6
Centrosomes(with centriole pairs)
Sisterchromatids
Chiasmata
Spindle
Tetrad
Nuclearenvelope
Chromatin
Centromere(with kinetochore)
Microtubuleattached tokinetochore
Tertads line up
Metaphaseplate
Homologouschromosomesseparate
Sister chromatidsremain attached
Pairs of homologouschromosomes split up
Chromosomes duplicateHomologous chromosomes
(red and blue) pair and exchangesegments; 2n = 6 in this example
INTERPHASE MEIOSIS I: Separates homologous chromosomes
PROPHASE I METAPHASE I ANAPHASE I
• Interphase and meiosis I
Figure 13.8
TELOPHASE I ANDCYTOKINESIS
PROPHASE II METAPHASE II ANAPHASE II TELOPHASE II ANDCYTOKINESIS
MEIOSIS II: Separates sister chromatids
Cleavagefurrow Sister chromatids
separate
Haploid daughter cellsforming
During another round of cell division, the sister chromatids finally separate;four haploid daughter cells result, containing single chromosomes
Two haploid cellsform; chromosomesare still doubleFigure 13.8
• Telophase I, cytokinesis, and meiosis II
Preformación (siglos 17 y 18)
Coherencia conceptual
1759 Kaspar Friedrich Wolff – epigénesis
Desarrollo – describe cambios progresivosen un individuo desde su concepción hastala madurez..
Organismos multicelulares sexuales -
Rearreglos extensos e interacciones = plan corporal (body plan) y celulasespecializadas.
Las células especializadas surgen gracias a una serie de condicines creadas en etapas anteriores.
En cada paso del desarrollo surgen nuevasestructuras como resultado de interacciones.
Cada interacción es incrementalmente restrictiva.
Determinación – localización citoplásmica - inducción
Durante la ovogénesis el óvulo (huevo) se prepara para la fertilización y para el comienzo del desarrollo.
El espermatozoide es una célula vacía llena de material genético a diferencia del huevo
El huevo se prepara durante la profase de meiosis I – producción de cuerpos polares (exceso decitoplasma)
Fertilización externa
Fertilización interna
Especificidad (quimiotaxis)
Se evita la polispermia
a. “fast block” cambio en el potencial de la membrana
b. “cortical reaction”
Fertilización
Fertilización
Restauración del número diploide
Activación del óvulo (a veces es lo único)
Partenogénesis
Eventos que ocurren durantela fecundación y el desarrollo temprano.
Segmentación (cleavage) en distintos organismos
“Cleavage furrow”
Isolecitos < Mesolecitos < Telolecitos < Centrolecitos
Holoblástico - (tunicados, equinodermos,tunicados, cefalocordados, nemerteos, y la mayor parte de los moluscos, marsupiales ymamíferos placentales)
Meroblástico – aves, reptiles, peces,anfibios, moluscos cefalópodos, y mamíferos Monotremos
Insectos = Centrolecitos
La cantidad de vitelo determina el tipo de desarrollo temprano del organismo
Directo Indirecto
Formación de capas embrionarias (Gastrulación)
Blastulación
Blastocelo
Blástula (Celoblástula – hueca y Stereoblástula – sólida) = 200 – varios miles de células
Se forma en todos los organismos multicelulares
El desarrollo continua mas allá de la blástula y se forman capas embrionarias(excepto en las esponjas)
Invaginación = gastrulación
archenteron
Tres capas embrionarias
EndodermoMesodermo
Ectodermo
Diploblástico
Triploblástico
Dos cavidades (celoma y sistema digestivo)
Celoma – cavidad corporal completamente revestida por mesodermo
Dos tipos de organismostripoblásticos
Los mamíferos son deuterostomados perosu celoma se forma mediante un procesoesquizocélicomodificado
Figure 08.14
Protostomes
Deuterostomes
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