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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
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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10-2
- or -
(must have QuickTake software installed on the computer you are using for this presentation)
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10-2
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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10-2
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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10-2
Cytokinesis usually occurs
at the same time as telophase.
after telophase.
during interphase.
during anaphase
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10-2
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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10-2
During mitosis, “sister” chromatids separate from one another during
telophase.
interphase.
anaphase.
metaphase.
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36. Chapter 10 Regulation of the Cell Cycle

37. Interest Grabber Answers
Knowing When to Stop
Suppose you had a paper cut on your finger. Although the cut may have bled and stung a little, after a few days, it will have disappeared, and your finger would be as good as new.
1. How do you think the body repairs an injury, such as a cut on a finger?
The cut is repaired by the production of new cells through cell division.
2. How long do you think this repair process continues?
Cell division continues until the cut is repaired.
3. What do you think causes the cells to stop the repair process?
Students will likely say that when the cut is filled in, there is no room for more cells to grow.

38. Control of Cell Division
Section 10-3
If center cells are removed, cells near the space will start to grow again.
SHOWS: Cell division
genes can be turned on
and off
Cells grow until they touch other cells

39. CELL DIVISION GENES Cells near injury are stimulated to divide
to heal and replace damaged/missing cells
and shut off when the
repair has been made.

40. CELL DIVISION GENES Some cells divide frequently
(some human skin cells divide once/hour)
Some cells divide occasionally
(liver cells divide about once/year)
Some cells don’t divide once they form
(nerve cells)

41. CELL CYCLE REGULATORS
In early 1980’s scientists discovered a protein in dividing cells that caused a
______________to form in
_______________ cells
Mitotic spindle
NON-dividing
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42. CELL CYCLE REGULATORS Levels of this protein rose and fell with
the cell cycle so it was named
__________ because it seemed to control the cell cycle.
A whole family of CYCLINS have since been discovered that regulate the _____________________
in EUKARYOTIC CELLS
CYCLIN
TIMING of CELL CYCLE
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43. OTHER REGULATORS INTERNAL
______________ REGULATORS Proteins that respond to events inside
the cell.
Allow cell cycle to proceed only if
certain processes have happened
EX: Cell can’t enter mitosis until all the
chromosomes have been copied

44. OTHER REGULATORS EXTERNAL
______________ REGULATORS Proteins that respond to events outside
the cell.
Signals tell cell to speed up or slow
down the cell cycle
EX:
Growth factors stimulate cells to divide Especially important during wound healing and
embryo development

45. EXTERNAL REGULATORS Molecules on the surface of neighboring
cells act as signals to slow down
or stop the
cell’s cycle.
These signals prevent
excessive growth and
keep tissues from
disrupting each other.
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46. Cancer cells have lost control of their cell division genes
SEM Image by: Riedell
CHO (Chinese Hamster Ovary) cells in culture

47. NO CONTACT INHIBITION Cancer cells don’t stop when they touch nearby
they just keep growing!
That’s what makes
a tumor.
See a video

48. Cancer cells Don’t stop dividing Like a “car with no brakes”
Can spread to new places (METASTASIS)
Carcinogens/Mutagens are substances that can damage DNA and cause cancer
Ex: Cigarette smoke (OR CHEW), Radiation, chemicals in environment, even viruses,