Download G 2 of Interphase

Desarrollo y patrones
arquitectónicos
Presentación 2
Dr. Robert J. Mayer
UPR en Aguadilla
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)
G2
Figure 12.5
• Mitosis consists of five distinct phases
– Prophase
– Prometaphase
G2 OF
INTERPHASE
Centrosomes
Chromatin
(with centriole pairs)
(duplicated)
Figure 12.6
Nucleolus
Nuclear Plasma
envelope membrane
PROPHASE
Early mitotic
spindle
Aster
Centromere
Chromosome, consisting
of two sister chromatids
PROMETAPHASE
Fragments
Kinetochore
of nuclear
envelope
Nonkinetochore
microtubules
Kinetochore
microtubule
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.
e
PROPHASE
Early mitotic
spindle
Aster
Centromere
Chromosome, consisting
of two sister chromatids
Prophase
• The chromatin fibers become
more tightly coiled, condensing
into discrete chromosomes
observable with a light
microscope.
• The nucleoli disappear.
PROMETAPHASE
• Each duplicated chromosome
appears as two identical sister
Fragments
Kinetochore
chromatids joined together.
of nuclear
• The mitotic spindle begins to form.
envelope
Nonkinetochore
It is composed
of the centrosomes
microtubules
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.
Kinetochore
microtubule
ere
PROMETAPHASE
Fragments
of nuclear
envelope
Kinetochore
Nonkinetochore
microtubules
Kinetochore
microtubule
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.
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
Metaphase
plate
Spindle
Centrosome at D
one spindle pole c
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 fullMETAPHASE
fledged chromosome.
• The two liberated chromosomes begin
Metaphase
moving toward opposite ends of the cell,
plate
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.
Spindle
ANAPHASE
Centrosome at Daughter
one spindle pole chromosomes
Cl
fur
Nuc
env
form
TELOPHASE AND CYTOKINESIS
Cleavage
furrow
Nuclear
envelope
forming
Nucleolus
forming
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.
– Metaphase
– Anaphase
– Telophase
METAPHASE
ANAPHASE
Metaphase
plate
Figure 12.6
Spindle
Centrosome at Daughter
one spindle pole chromosomes
TELOPHASE AND CYTOKINESIS
Cleavage
furrow
Nuclear
envelope
forming
Nucleolus
forming
• Interphase and meiosis I
MEIOSIS I: Separates homologous chromosomes
INTERPHASE
PROPHASE I
METAPHASE I
ANAPHASE I
Sister chromatids
remain attached
Centromere
(with kinetochore)
Centrosomes
(with centriole pairs)
Sister
chromatids
Nuclear
envelope
Chiasmata
Spindle
Metaphase
plate
Homologous
Microtubule
chromosomes
Tetrad
attached to
Chromatin
separate
kinetochore
Pairs of homologous
Chromosomes duplicate
Tertads line up
chromosomes split up
Homologous chromosomes
(red and blue) pair and exchange
Figure 13.8
segments; 2n = 6 in this example
• Telophase I, cytokinesis, and meiosis II
MEIOSIS II: Separates sister chromatids
TELOPHASE I AND
CYTOKINESIS
PROPHASE II
Cleavage
furrow
Figure 13.8
Two haploid cells
form; chromosomes
are still double
METAPHASE II
ANAPHASE II
Sister chromatids
separate
TELOPHASE II AND
CYTOKINESIS
Haploid daughter cells
forming
During another round of cell division, the sister chromatids finally separate;
four haploid daughter cells result, containing single chromosomes
Preformación (siglos 17 y 18)
Coherencia conceptual
1759 Kaspar Friedrich Wolff – epigénesis
Desarrollo – describe cambios progresivos
en un individuo desde su concepción hasta
la madurez..
Organismos multicelulares sexuales Rearreglos extensos e interacciones =
plan corporal (body plan) y celulas
especializadas.
Las células especializadas surgen gracias
a una serie de condicines creadas en
etapas anteriores.
En cada paso del desarrollo surgen nuevas
estructuras 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 de
citoplasma)
Fertilización
Fertilización externa
Fertilización interna
Especificidad (quimiotaxis)
Se evita la polispermia
a. “fast block” cambio en el potencial de
la membrana
b. “cortical reaction”
Fertilización
Restauración del número diploide
Activación del óvulo (a veces es lo único)
Partenogénesis
Eventos que ocurren durante
la 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 y
mamíferos 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)
archenteron
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
Tres capas embrionarias
Endodermo
Mesodermo
Ectodermo
Diploblástico
Triploblástico
Dos cavidades (celoma y sistema digestivo)
Celoma – cavidad corporal completamente revestida por mesodermo
Dos tipos de
organismos
tripoblásticos
Los mamíferos son
deuterostomados pero
su celoma se forma
mediante un proceso
esquizocélico
modificado
Figure 08.14
Protostomes
Deuterostomes