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