chapter8_part1
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How Cells Reproduce
Chapter 8
Part 1
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8.1 Impacts/Issues
Henriettas Immortal Cells
Runaway cell divisions killed Henrietta Lacks, but her cells live on in research laboratories
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Fig. 8-1a, p. 136
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Fig. 8-1b, p. 136
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Video: Henrietta's immortal cells
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8.2 Multiplication by Division
A cell reproduces by dividing in two
Each descendant cell receives a full set of chromosomes and some cytoplasm
Nuclear division mechanisms partition chromosomes of a parent cell into new nuclei
The cytoplasm divides by a separate mechanism
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Divisions of a Fertilized Egg
Third division of an early frog embryo
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Two Methods of Nuclear Division: Mitosis
Mitosis
Nuclear division process that maintains the
chromosome number
Basis of body growth, tissue repair and
replacement in multicelled eukaryotes; also
asexual reproduction in some plants, animals,
fungi, and protists
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Two Methods of Nuclear Division: Meiosis
Meiosis
Nuclear division process that halves the
chromosome number
Basis of sexual reproduction in multicelled
eukaryotes; precedes the formation of gametes or
sexual spores
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Comparison of Division Mechanisms
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8.3 The Life of a Cell
A cell cycle starts when a new cell forms, and ends when the cell reproduces
Cell cycle
A series of events from the time a cell forms until
its cytoplasm divides
Includes three phases: interphase, mitosis, and
cytoplasmic division
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Interphase
Most of a cells activities, including DNA replication, occur in interphase
Interphase
In a eukaryotic cell cycle, the interval between
mitotic divisions when a cell grows, roughly
doubles the number of its cytoplasmic
components, and replicates its DNA
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Three Stages of Interphase
G1
1st interval (gap) of growth before DNA replication
S
Interval of synthesis (DNA replication)
G2
2nd interval (gap) when the cell prepares to divide
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Controls of Cell Division
Different types of cells proceed through the cell cycle at different rates
Gene expression controls regulate the cell cycle at different points
Loss of cell cycle controls results in cancer
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Chromosomes During the Cell Cycle
Human body cells have 23 chromosome pairs
Except for male sex chromosomes, the chromosomes of each pair are homologous
Homologous
Two members of a pair of chromosomes with the
same length, shape, and genes
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Chromosomes During the Cell Cycle
Mitosis maintains the chromosome number
Each chromosome is duplicated
Each new cell receives identical chromosomes
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Fig. 8-4, p. 139
A An unduplicated
pair of chromosomes
in a cell in G1.
B By G2, each
chromosome has
been duplicated.
C Mitosis and
cytoplasmic division
package one copy of
each chromosome into
each of two new cells.
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C Mitosis and
cytoplasmic division
package one copy of
each chromosome into
each of two new cells.
Fig. 8-4, p. 139
A An unduplicated
pair of chromosomes
in a cell in G1.
B By G2, each
chromosome has
been duplicated.
Stepped Art
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Eukaryotic Cell Cycle
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Fig. 8-3, p. 138
mitosis ends,
interphase beginsinterphase ends,
mitosis begins
12
3
4
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Animation: The cell cycle
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8.4 Mitosis
At the end of interphase, a cells duplicated chromosomes condense tightly in preparation
for nuclear division (mitosis)
Each chromosome consists of two sister
chromatids
Mitosis has four stages: prophase, metaphase, anaphase, and telophase
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Prophase
Prophase
Chromosomes condense and spindle forms
Nuclear envelope breaks up
Spindle microtubules attach to chromosomes
Spindle
Dynamically assembled and disassembled array
of microtubules that moves chromosomes during
nuclear division
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Metaphase
Metaphase
Duplicated homologous chromosomes line up at
the spindle equator (halfway between spindle
poles)
Sister chromatids begin to move apart toward
opposite spindle poles
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Anaphase
Anaphase
Microtubules separate the sister chromatids of
each chromosome and pull them toward opposite
spindle poles
Each DNA molecule is now a separate
chromosome
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Telophase
Telophase
Two clusters of chromosomes arrive at the
spindle poles and decondense; new nuclei form
End of mitosis
Nuclear envelopes form around the two clusters
of chromosomes, forming two new nuclei with the
parental chromosome number
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Mitosis
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Fig. 8-5a, p. 140
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Fig. 8-5b, p. 141
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Fig. 8-5b (1), p. 141
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Fig. 8-5b (1), p. 141
centrosome
1 Early ProphaseMitosis begins. In
the nucleus, the DNA
begins to appear grainy as
it organizes and condenses.
The centrosome is duplicated.
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Fig. 8-5b (2), p. 141
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Fig. 8-5b (2), p. 141
2 Prophase The chromosomes become
visible as distinct structures
as they condense further.
Microtubules assemble
and move one of the two
centrosomes to the opposite
side of the nucleus, and the
nuclear envelope breaks up.
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Fig. 8-5b (3), p. 141
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Fig. 8-5b (3), p. 141
pole pole3 Transition to Metaphase
The nuclear envelope
is gone, and the
chromosomes are at their
most condensed. Spindle
microtubules assemble and
attach sister chromatids to
opposite spindle poles. microtubule of
spindle
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Fig. 8-5b (4), p. 141
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Fig. 8-5b (4), p. 141
4 Metaphase
All of the chromosomes are
aligned midway between the
spindle poles. Microtubules
attach each chromatid to one
of the spindle poles, and its
sister to the opposite pole.
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Fig. 8-5b (5), p. 141
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Fig. 8-5b (5), p. 141
5 Anaphase
Motor proteins
moving along spindle
microtubules drag the
chromatids toward the spindle
poles, and the sister chromatids
separate. Each sister chromatid
is now a separate chromosome.
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Fig. 8-5b (6), p. 141
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Fig. 8-5b (6), p. 141
6 TelophaseThe chromosomes reach
the spindle poles and
decondense. A nuclear
envelope forms around
each cluster. Mitosis is
over.
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Animation: Mitosis-step-by-step
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Fig. 8-5b (6), p. 141
Stepped Art
6) Telophase
The chromosomes reach the spindle poles and decondense. A
nuclear envelope forms around each cluster. Mitosis is over.
centrosome1) Early Prophase
Mitosis begins. In the nucleus, the DNA
begins to appear grainy as it organizes and
condenses. The centrosome is duplicated.
2) Prophase
The chromosomes become visible as distinct structures
as they condense further. Microtubules assemble
and move one of the two centrosomes to the opposite
side of the nucleus, and the nuclear envelope breaks up.
pole pole3) Transition to Metaphase
The nuclear envelope is gone, and the chromosomes
are at their most condensed. Spindle microtubules
assemble and attach sister chromatids to opposite
spindle poles.
microtubule of
spindle
4) Metaphase
All of the chromosomes are aligned midway between the spindle
poles. Microtubules attach each chromatid to one of the spindle
poles, and its sister to the opposite pole.
5) Anaphase
Motor proteins moving along spindle microtubules drag the
chromatids toward the spindle poles, and the sister chromatids
separate. Each sister chromatid is now a separate chromosome.
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Animation: Spindle apparatus
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Animation: Mechanisms for chromosome
movement
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3D Animation: Mitosis
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Animation: Mitosis
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8.5 Cytoplasmic Division Mechanisms
A cells cytoplasm usually divides after mitosis, forming two cells, each with its own nucleus
Mechanisms of cytoplasmic division differ between animal cells and plant cells
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Cytoplasmic Division in Animal Cells
In animal cells, a contractile ring pinches the cytoplasm in two
Contractile ring
Band of actin and myosin filaments that contracts
to form the cleavage furrow
Cleavage furrow
In a dividing animal cell, the indentation where
cytoplasmic division will occur
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Cytoplasmic Division of an Animal Cell
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Fig. 8-6a, p. 142
A After mitosis is
completed, the spindle
begins to disassemble.
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Fig. 8-6b, p. 142
B At the midpoint of the former spindle, a
ring of actin and myosin filaments attached
to the plasma membrane contracts.
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Fig. 8-6c, p. 142
C This contractile ring pulls the
cell surface inward as it shrinks.
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Fig. 8-6d, p. 142
D The ring contracts until
it pinches the cell in two.
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Animation: Cytoplasmic division
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Cytoplasmic Division in Plant Cells
In plant cells, a cell-plate forms midway between the spindle poles and partitions the cytoplasm
when it connects to the parent cell wall
Cell plate
After nuclear division in a plant cell, a diskshaped
structure that forms a cross-wall between the two
new nuclei
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Cytoplasmic Division of a Plant Cell
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Fig. 8-7a, p. 143
A The plane of
division was
established before
mitosis began.
Vesicles cluster here
when mitosis ends.
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Fig. 8-7b, p. 143
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Fig. 8-7b, p. 143
cell
plate
forming
B As the vesicles
fuse with each other,
they form a cell plate
along the plane of
division.
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Fig. 8-7c, p. 143
C The cell plate expands outward along the
plane of division. When it reaches the plasma
membrane, it attaches to the membrane and
partitions the cytoplasm.
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Fig. 8-7d, p. 143
D The cell plate
matures as two new
cell walls that join
with the parent cell
wall, so each
descendant cell
becomes enclosed
by its own cell wall.