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10-2 Cell Division
Photo Credit: © CAMR/A.B. Dowsett/Science Photo Library/Photo Researchers, Inc.
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Cell Division
In eukaryotes, cell division occurs in two major stages. The first stage, division of the cell nucleus, is called mitosis. The second stage, division of the cell cytoplasm, is called cytokinesis.
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3. Chromosomes
Chromosomes
Genetic information is passed from one generation to the next on chromosomes.
Before cell division, each chromosome is duplicated, or copied.

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Chromosomes
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Chromosomes
Each chromosome consists of two identical “sister” chromatids. Each pair of chromatids is attached at an area called the centromere.
Sister chromatids
Photo Credit: © Gunther F. Bahr/AFIP/Stone
Centromere
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Chromosomes
When the cell divides, the chromatids separate. Each new cell gets one chromatid.
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The Cell Cycle
Cell Cycle
The cell cycle is the series of events that cells go through as they grow and divide.
Interphase is the period of growth that occurs between cell divisions.
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The Cell Cycle
During the cell cycle:
a cell grows
prepares for division
divides to form two daughter cells, each of which begins the cycle again
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The cell cycle consists of four phases:
G1 (First Gap Phase)
S Phase
G2 (Second Gap Phase)
M Phase
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10. Events of the Cell Cycle
During G1, the cell
increases in size
synthesizes new proteins and organelles
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11. Events of the Cell Cycle
During the S phase,
chromosomes are replicated
DNA synthesis takes place
Once a cell enters the S phase, it usually completes the rest of the cell cycle.
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12. Events of the Cell Cycle
The G2 Phase (Second Gap Phase)
organelles and molecules required for cell division are produced
Once G2 is complete, the cell is ready to start the M phase—Mitosis
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13. Events of the Cell Cycle
During the cell cycle, the cell grows, replicates its DNA, and divides into two daughter cells. DNA synthesis takes place during the S phase. Cell division takes place during the M phase. G1 and G2 are gap phases.
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Mitosis
Mitosis
Biologists divide the events of mitosis into four phases: (PMAT)
Prophase
Metaphase
Anaphase
Telophase
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Mitosis
Most eukaryotic cells go through a regular cycle of interphase, mitosis and cytokinesis. Mitosis has four phases: Prophase, Metaphase, Anaphase and Telophase. The events shown here are typical of animal cells.
Mitosis
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16. Chromosomes (paired chromatids)
Mitosis
Section 10-2
Spindle forming
Prophase
Prophase
Chromosomes (paired chromatids)
Centromere
Most eukaryotic cells go through a regular cycle of interphase, mitosis and cytokinesis. Mitosis has four phases: Prophase, Metaphase, Anaphase and Telophase. The events shown here are typical of animal cells.
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Mitosis
Spindle
forming
Prophase
Prophase is the first and longest phase of mitosis.
The centrioles separate and take up positions on opposite sides of the nucleus.
Centromere
Chromosomes
(paired chromatids)
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Mitosis
Spindle
forming
The centrioles lie in a region called the centrosome. The centrosome helps to organize the spindle, a fanlike microtubule structure that helps separate the chromosomes.
Centromere
Chromosomes
(paired chromatids)
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Mitosis
Spindle
forming
Chromatin condenses into chromosomes. The centrioles separate and a spindle begins to form. The nuclear envelope breaks down.
Centromere
Chromosomes
(paired chromatids)
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Mitosis
Metaphase
Centriole
Spindle
Centriole
Metaphase
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Mitosis
Centriole
Metaphase
The second phase of mitosis is metaphase.
The chromosomes line up across the center of the cell.
Microtubules connect the centromere of each chromosome to the poles of the spindle.
Spindle
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22. Individual chromosomes
Mitosis
Anaphase
Individual chromosomes
Anaphase
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Mitosis
Anaphase
Anaphase is the third phase of mitosis.
The sister chromatids separate into individual chromosomes.
The chromosomes continue to move until they have separated into two groups.
Individual
chromosomes
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24. Nuclear envelope reforming
Mitosis
Telophase
Nuclear envelope reforming
Telophase
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Mitosis
Telophase
Telophase is the fourth and final phase of mitosis.
Chromosomes gather at opposite ends of the cell and lose their distinct shape.
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Mitosis
A new nuclear envelope forms around each cluster of chromosomes.
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Cytokinesis
Cytokinesis
Cytokinesis
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Cytokinesis
During cytokinesis, the cytoplasm pinches in half. Each daughter cell has an identical set of duplicate chromosomes
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Cytokinesis in Plants
In plants, a structure known as the cell plate forms midway between the divided nuclei.
Cell plate
Cell wall
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The series of events that cells go through as they grow and divide is called
the cell cycle.
mitosis.
interphase.
cytokinesis.
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The phase of mitosis during which the chromosomes line up across the center of the cell is
prophase.
metaphase.
anaphase.
telophase.
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Cytokinesis usually occurs
at the same time as telophase.
after telophase.
during interphase.
during anaphase
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DNA replication takes place during the
S phase of the cell cycle.
G1 phase of the cell cycle.
G2 phase of the cell cycle.
M phase of the cell cycle.
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During mitosis, “sister” chromatids separate from one another during
telophase.
interphase.
anaphase.
metaphase.
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35. 10-3 Regulating the Cell Cycle
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36. Controls on Cell Division
Experiments show that normal cells will reproduce until they come into contact with other cells.
When cells come into contact with other cells, they respond by not growing.
This demonstrates that controls on cell growth and division can be turned on and off.
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37. Controls on Cell Division
Contact Inhibition
Cells in a petri dish will continue to grow until they come into contact with other cells.
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Cell Cycle Regulators
How is the cell cycle regulated?
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Cell Cycle Regulators
Cell Cycle Regulators The cell cycle is regulated by a specific protein. The amount of this protein in the cell rises and falls in time with the cell cycle. Scientists called this protein cyclin because it seemed to regulate the cell cycle. Cyclins regulate the timing of the cell cycle in eukaryotic cells.
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Cell Cycle Regulators
Cyclins were discovered during a similar experiment to this one.
The timing of the cell cycle is regulated by cyclins. When cytoplasm from a cell in mitosis is injected into another cell, the second cell enters into mitosis. The reason for this effect is a protein called cyclin, which triggers cell division.
A sample of cytoplasm is removed from a cell in mitosis.
The sample is injected into a second cell in G2 of interphase.
As result, the second cell enters mitosis.
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Cell Cycle Regulators
Internal Regulators 
Internal regulators allow the cell cycle to proceed only when certain processes have happened inside the cell.
Example: p53 Gene that regulates the passage into mitosis
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Cell Cycle Regulators
External Regulators 
Proteins that respond to events outside the cell are called external regulators.
External regulators direct cells to speed up or slow down the cell cycle.
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43. Uncontrolled Cell Growth
Cancer is a disorder in which some of the body's own cells lose the ability to control growth.
How are cancer cells different from other cells?
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44. Uncontrolled Cell Growth
Cancer cells do not respond to the signals that regulate the growth of most cells.
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45. Uncontrolled Cell Growth
Cancer cells divide uncontrollably and form masses of cells called tumors that can damage the surrounding tissues. Cancer cells may break loose from tumors and spread throughout the body, disrupting normal activities and causing serious medical problems or even death.
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The cell cycle is believed to be controlled by proteins called
spindles.
cyclins.
regulators.
centrosomes.
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Proteins that respond to events inside the cell are called
internal regulators.
external regulators.
cyclins.
growth factors.
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10-3
Once a multicellular organism reaches adult size, the cells in its body
stop dividing.
grow and divide at different rates, depending on the type.
have the same life span between cell divisions.
undergo cell division randomly.
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10-3
One effect of an internal regulator is that a cell will not begin mitosis until
it becomes too large.
the cell’s growth is stimulated.
it is in physical contact with other cells.
all its chromosomes have been replicated.
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One factor common to almost all cancer cells is
a lack of cyclin.
a defect in gene p53.
exposure to tobacco smoke.
exposure to radiation.
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