cell division and reproduction © 2012 pearson education, inc
TRANSCRIPT
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CELL DIVISION AND REPRODUCTION
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Cell division plays many important roles in the lives of organisms
Organisms reproduce their own kind, a key characteristic of life.
Cell division
– is reproduction at the cellular level,
– requires the duplication of chromosomes, and
– sorts new sets of chromosomes into the resulting pair of daughter cells.
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Cell division is used
– for reproduction of single-celled organisms,
– growth of multicellular organisms from a fertilized egg into an adult,
– repair and replacement of cells, and
– sperm and egg production.
Cell division plays many important roles in the lives of organisms
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Cell division plays many important roles in the lives of organisms
Living organisms reproduce by two methods.
– Asexual reproduction
– produces offspring that are identical to the original cell or organism and
– involves inheritance of all genes from one parent.
– Sexual reproduction
– produces offspring that are similar to the parents, but show variations in traits and
– involves inheritance of unique sets of genes from two parents.
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Figure 8.1A
Asexual Reproduction
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Figure 8.1D
Sexual reproduction produces offsprings with unique combination of genes
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Figure 8.1E
Dividing cells in an human embryo A human kidney
cell dividing
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Prokaryotes (bacteria) reproduce by binary fission (“dividing in half”).
The chromosome of a prokaryote is
– a singular circular DNA molecule associated with proteins and
– much smaller than those of eukaryotes.
Prokaryotes reproduce by binary fission
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Binary fission of a prokaryote occurs in three stages:
1. duplication of the chromosome and separation of the copies,
2. continued elongation of the cell and movement of the copies, and
3. division into two daughter cells.
Prokaryotes reproduce by binary fission
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Figure 8.2A_s3
Plasmamembrane
Cell wall
Duplication of the chromosomeand separation of the copies
Continued elongation of thecell and movement of the copies
Prokaryoticchromosome
1
2
3Division into
two daughter cells
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Figure 8.2B
Prokaryotic chromosomes
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THE EUKARYOTIC CELL CYCLE AND MITOSIS
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Eukaryotic cells
– are more complex and larger than prokaryotic cells,
– have more genes, and
– store most of their genes on multiple chromosomes within the nucleus.
The large, complex chromosomes of eukaryotes duplicate with each cell division
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Eukaryotic chromosomes are composed of chromatin consisting of
– one long DNA molecule and
– proteins that help maintain the chromosome structure and control the activity of its genes.
To prepare for division, the chromatin becomes
– highly compact and
– visible with a microscope.
The large, complex chromosomes of eukaryotes duplicate with each cell division
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Figure 8.3A
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Figure 8.3B
Sisterchromatids
Chromosomes
Centromere
Chromosomeduplication
Sisterchromatids
Chromosomedistribution
to thedaughter
cells
DNA molecules
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Before a eukaryotic cell begins to divide, it duplicates all of its chromosomes, resulting in
– two copies called sister chromatids
– joined together by centromere.
When a cell divides, the sister chromatids
– separate from each other, now called chromosomes, and
– sort into separate daughter cells.
The large, complex chromosomes of eukaryotes duplicate with each cell division
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The cell cycle is an ordered sequence of events that extends
– from the time a cell is first formed from a dividing parent cell
– until its own division.
The cell cycle multiplies cells
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The cell cycle consists of two stages, characterized as follows:
1. Interphase: duplication of cell contents
– G1—growth, increase in cytoplasm
– S—duplication of chromosomes
– G2—growth, preparation for division
2. Mitotic phase: division
– Mitosis—division of the nucleus
– Cytokinesis—division of cytoplasm
The cell cycle multiplies cells
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Figure 8.4
G1
(first gap)S
(DNA synthesis)
G2
(second gap)
M
CytokinesisM
itosi
s
I N T E R P H A S E
PHASE
TT
MI
OIC
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Mitosis progresses through a series of stages:
– prophase,
– prometaphase,
– metaphase,
– anaphase, and
– telophase.
Cytokinesis often overlaps telophase.
Cell division is a continuum of dynamic changes
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A mitotic spindle is
– required to divide the chromosomes,
– composed of microtubules, and
– produced by centrosomes, structures in the cytoplasm that
– organize microtubule arrangement and
– contain a pair of centrioles in animal cells.
Cell division is a continuum of dynamic changes
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Video: Sea Urchin (time lapse)
Video: Animal Mitosis
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Figure 8.5_1
INTERPHASEMITOSIS
Prophase Prometaphase
Centrosome
Early mitoticspindle
Chromatin
Fragments ofthe nuclearenvelope
Kinetochore
Centrosomes(with centriole pairs)
Centrioles
Nuclearenvelope
Plasmamembrane
Chromosome,consisting of twosister chromatids
CentromereSpindlemicrotubules
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Interphase
– The cytoplasmic contents double,
– two centrosomes form,
– chromosomes duplicate in the nucleus during the S phase, and
– nucleoli, sites of ribosome assembly, are visible.
Cell division is a continuum of dynamic changes
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Figure 8.5_left
INTERPHASEMITOSIS
Prophase Prometaphase
CentrosomeEarly mitoticspindle
Chromatin
Fragments ofthe nuclear envelope
Kinetochore
Centrosomes(with centriole pairs)
Centrioles
Nuclearenvelope
Plasmamembrane
Chromosome,consisting of twosister chromatids
Centromere Spindlemicrotubules
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Prophase
– In the cytoplasm microtubules begin to emerge from centrosomes, forming the spindle.
– In the nucleus
– chromosomes coil and become compact and
– nucleoli disappear.
Cell division is a continuum of dynamic changes
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Prometaphase
– Spindle microtubules reach chromosomes, where they
– attach at kinetochores on the centromeres of sister chromatids and
– move chromosomes to the center of the cell through associated protein “motors.”
– Other microtubules meet those from the opposite poles.
– The nuclear envelope disappears.
Cell division is a continuum of dynamic changes
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Figure 8.5_5
MITOSIS
AnaphaseMetaphase Telophase and Cytokinesis
Metaphaseplate Cleavage
furrow
NuclearenvelopeformingDaughter
chromosomesMitoticspindle
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Figure 8.5_right
MITOSIS
AnaphaseMetaphase Telophase and Cytokinesis
Metaphaseplate
Cleavagefurrow
Nuclearenvelopeforming
Daughterchromosomes
Mitoticspindle
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Metaphase
– The mitotic spindle is fully formed.
– Chromosomes align at the cell equator.
– Kinetochores of sister chromatids are facing the opposite poles of the spindle.
Cell division is a continuum of dynamic changes
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Anaphase – Sister chromatids separate at the centromeres.
– Daughter chromosomes are moved to opposite poles of the cell as
– motor proteins move the chromosomes along the spindle microtubules and
– kinetochore microtubules shorten.
– The cell elongates due to lengthening of nonkinetochore microtubules.
Cell division is a continuum of dynamic changes
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Telophase– The cell continues to elongate.
– The nuclear envelope forms around chromosomes at each pole, establishing daughter nuclei.
– Chromatin uncoils and nucleoli reappear.
– The spindle disappears.
Cell division is a continuum of dynamic changes
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During cytokinesis, the cytoplasm is divided into separate cells.
The process of cytokinesis differs in animal and plant cells.
Cell division is a continuum of dynamic changes
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In animal cells, cytokinesis occurs as
1. a cleavage furrow forms from a contracting ring of microfilaments, interacting with myosin, and
2. the cleavage furrow deepens to separate the contents into two cells.
Cytokinesis differs for plant and animal cells
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Figure 8.6A
CytokinesisCleavage
furrow Contracting ring ofmicrofilaments
Daughtercells
Cleavagefurrow
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Figure 8.6A_1
Cleavagefurrow
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Figure 8.6A_2
Cleavagefurrow Contracting ring of
microfilaments
Daughtercells
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In plant cells, cytokinesis occurs as1. a cell plate forms in the middle, from vesicles
containing cell wall material,
2. the cell plate grows outward to reach the edges, dividing the contents into two cells,
3. each cell now possesses a plasma membrane and cell wall.
Cytokinesis differs for plant and animal cells
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Animation: Cytokinesis
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Figure 8.6B
Cytokinesis
Cell wallof theparent cell
Daughternucleus
Cell wall
Plasmamembrane
Vesiclescontainingcell wallmaterial
Cell plateforming
Newcell wall
Cell plate Daughtercells
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Figure 8.6B_1
Cell wallof theparent cell
Daughternucleus
Cell plateforming
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Figure 8.6B_2
Cell wall
Plasmamembrane
Vesiclescontainingcell wallmaterial
Newcell wall
Cell plate Daughtercells
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When the cell cycle operates normally, mitosis produces genetically identical cells for
– growth,
– replacement of damaged and lost cells, and
– asexual reproduction.
Review: Mitosis provides for growth, cell replacement, and asexual reproduction
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Video: Hydra Budding
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Figure 8.10A
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Figure 8.10B
Cell replacement (in bone marrow)
Asexual reproduction (of a hydra)
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Cancer cells
– start out as normal body cells,
– undergo genetic mutations,
– lose the ability to control the tempo of their own division, and
– causing disease.
Introduction
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Figure 8.0_3