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Cell Division
Introduction
Just like a butterfly passes through different phases (such as caterpillar, chrysalis, and adult butterfly)
there are a series of phases in a cell's life as it gets ready to divide. The sequence of phases leading up to cell
division, ending with cell division itself, is called the cell cycle. Each new cell must be identical to the original
with a complete copy of the organism’s DNA. The process of cell division in eukaryotic cells is carefully
controlled because it allows organisms to grow, repair injuries, and reproduce. If the cell cycle is not carefully
controlled, it can cause a disease called cancer in which the cells divide out of control. A tumor can result from
this kind of growth.
Chromatin, Chromosomes, and Chromatids, Oh My!
Throughout the cell cycle, DNA takes on different shapes and each of those shapes has another name.
In the beginning of the cell cycle, the DNA looks like a pile of string, which is called chromatin. At the
beginning of the cell cycle, the chromatin is copied, so that the new cell will have an identical copy of the
original DNA. Before the nucleus divides, the DNA in the nucleus wraps around proteins to form
chromosomes, which look like worms and arrange themselves into an “X” shape. Each half of the “X” is
identical to the other and are called sister chromatids. Each organism has a unique number of chromosomes.
In human cells, our DNA is divided up into 23 pairs of chromatids, or 46 chromosomes.
The Cell Cycle
Like a human life cycle, which is made up of
different phases (childhood, adolescence,
adulthood) the cell cycle also occurs in a series of
phases. These steps can be divided into three main
components: interphase, mitosis, and cytokinesis.
Interphase is the stage when the cell mostly
performs its “everyday” functions. For example, it is
when a kidney cell does what a kidney cell is
supposed to do. The cell also gets ready to divide
during this time. The nucleus divides during mitosis,
and then the cell splits in half during cytokinesis. A
summary of all of the phases is pictured to the right.
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Interphase
Most of the cell cycle consists of interphase, the time between cell divisions. Interphase can be divided
into three stages:
1. The first growth phase (G1): During the G1 stage, the cell doubles in size and doubles the number of
organelles.
2. The synthesis phase (S): The DNA is replicated during this phase. In other words, an identical copy of
the cell’s DNA is made. This ensures that each new cell has a set of genetic material identical to that of
the parental cell.
3. The second growth phase (G2): Proteins are synthesized that will help the cell divide. At the end of
interphase, the cell is ready to enter mitosis.
Mitosis
During mitosis, the nucleus divides. One nucleus becomes two nuclei, each with an identical set of DNA.
Mitosis consists of four separate phases:
1. Prophase: The DNA coils into chromosomes, the membrane around the nucleus begins to disappear,
cylindrical organelles (called centrioles) move to opposite ends of the cell, and thread-like structures
(called spindle fibers) sprout from the centrioles.
2. Metaphase: The nuclear membrane has disappeared completely, the chromosomes line up in the
middle of the cell, and spindle fibers attach to the chromosomes at the center (an area called the
centromere).
3. Anaphase: The spindle fibers pull the chromosomes apart at the centromere and pull them to opposite
ends of the cell.
4. Telophase: A nuclear membrane forms around each group of chromatids, the chromatids unwind, and
cytokinesis begins.
Cytokinesis
Mitosis is followed by
cytokinesis, when the cytoplasm
divides, resulting in two cells. After
cytokinesis, cell division is
complete. The one parent cell (the
dividing cell) forms two genetically
identical daughter cells (the cells
that divide from the parent cell).
The term "genetically identical"
means that each cell has an
identical set of DNA, and this DNA
is also identical to that of the
parent cell.
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Review of “Cell Division” Reading
1. What do chromatin, chromosomes, and chromatids have in common? How are they different?
2. What are the three parts of the cell cycle?
3. What happens during mitosis?
4. What are the four phases of mitosis, in the correct order?
5. What is cytokinesis, and when does it occur?
6. How do daughter cells compare to the parent cell?
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Cell Division Notes
The cell cycle is the process by which cells replicate and divide. There are three parts: interphase
(preparation), mitosis (nuclear division), and cytokinesis (splitting).
Why do cells divide?
How do cells know how to divide?
1.
2.
The ________ has the ____________________ for
3.
all the cell’s activities.
How long does it take in embryonic (offspring) cells?
How long does it take for body cells (adult human)?
1. Interphase – “COPYING”
 Cell ____________________ in size.
 ________ (looks like a pile of string) replicates.
 ______________________ double in number.
2. Prophase – “PAIRING”
 DNA ____________ into chromosomes, which pair with their copy
 Centrioles move toward __________________ poles.
 Spindle fibers __________.
 Nuclear membrane begins to __________________.
3. Metaphase – “MIDDLE”
 Nucleus has ____________________ completely.
 Chromosomes line up in the _______________ of the cell.
 Spindle fibers ______________ to centromeres.
4. Anaphase – “APART”
 Centromeres __________________.
 Chromatids ________________ and move toward opposite poles.
5. Telophase – “TWO”
 Nuclear membrane _____________ around each group of chromosomes.
 Chromosomes _____________.
 Cytokinesis ____________.
6. Cytokinesis – “CYTOPLASM SPLITS”
 Cytoplasm ______________.
 ________ cell becomes _________ cells.
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Cell Cycle Labeling
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Formative Assessment: Cell Division
DIRECTIONS: Match each phase with its “theme.”
_____ 1. Interphase
A. Apart
_____ 2. Prophase
B. Copying
DIDIRECTIONS: Match each term with its definition.
_____ 7. Centriole
A. Half an “X” shape.
_____ 8. Centromere
B. The “X” shapes.
_____ 9. Chromatid
C. Cylindrical organelle.
_____ 3. Metaphase
C. Cytoplasm Splits
_____ 4. Anaphase
D. Middle
_____ 5. Telophase
E. Pairing
_____ 10. Chromosome
D. Thread-like structures.
_____ 6. Cytokinesis
F. Two
_____ 11. Spindle Fibers
E. Center of the “X.”
DIRECTIONS: Number the pictures to show the correct order of the phases of cell division.
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Lab: Cell Division
Objectives:

Use models to study cell division.

Learn that cell division is the process by which cells pass on their genetic information.
What will happen to the number of chromosomes during cell division?
Hypothesis:
If a cell goes through cell division, then the number of chromosomes will ______________________________
__________________________________________________________________________________________
.
Warm-Up Questions:
1. Why do cells divide?
______________________________________________________________________.
2. During cell division, one cell becomes ________.
3. How many chromosomes do humans have? ________.
4. How does the DNA of a daughter cell compare to the parent cell? _________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
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Data Table:
Drawing
Before
Interphase
End of
Interphase/
Beginning of
Prophase
End of
Prophase/
Beginning of
Metaphase
End of
Metaphase/
Beginning of
Anaphase
End of
Anaphase/
Beginning of
Telophase
End of
Telophase/
Beginning of
Cytokinesis
End of
Cytokinesis/Be
ginning of
Interphase
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Number
of Cells
# of Nuclei
(per cell)
# of
Chromatids
(per cell)
Cell
Membrane
Present?
Nuclear
Membrane
Present?
Formative Assessment #2: Cell Division
DIRECTIONS: Match the event(s) to the phase in which they happen.
_____ 1. Anaphase
A. Everything in the cell doubles.
_____ 2. Cytokinesis
B. The cytoplasm splits.
_____ 3. Interphase
C. Nuclear membranes form around each set of chromosomes, which unwind.
_____ 4. Metaphase
D. Centromeres divide and chromatids move to opposite ends.
_____ 5. Prophase
E. Chromosomes line up in the middle of the cell.
_____ 6. Telophase
F. DNA coils into chromosomes and nuclear membrane begins to disappear.
DIRECTIONS: Match each term with its definition.
_____ 7. Centriole
F. Centers of chromosomes.
_____ 8. Centromere
G. Thread-like structures that attach to centromeres.
_____ 9. Chromatid
H. Cylindrical organelle that sprouts spindle fibers.
_____ 10. Chromosome
I. Half of a chromosome.
_____ 11. Spindle Fibers
J. Coiled structures of DNA.
DIRECTIONS: Number the pictures to show the correct order of the phases of cell division.
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