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The Cell Cycle, or Cell Division
The regular sequence of growth and division that eukaryotic somatic cells undergo is
known as the cell cycle. Somatic cells multiply by dividing. This process allows living
organisms to grow & replace worn out or injured cells. However, cell division doesn’t happen at
the same rate in different types of tissue. The rate of cell division depends on the function of the
tissue and how often the cells need to be replaced.
Stage One of the Cell Cycle: Interphase
During interphase, the cell:
1. Grows to full size and produces all the structures it needs
2. Produces structures to use during cell division into two cells
3. Makes an exact copy of DNA in the nucleus, known as replication. At the end of DNA
replication, the cell contains two identical sets of DNA.
Stage Two of the Cell Cycle: Mitosis
Mitosis occurs once interphase is complete. It is the stage during which the cell’s nucleus
divides into two new nuclei. During mitosis, one copy of the DNA is distributed into
each of two daughter cells. Scientists divide mitosis into four parts, or phases:
1. Prophase (pro- “first” & -phase “stage”) occurs as the nucleus prepares for cell division.
a. Chromatin condenses to form chromosomes. Chromosomes can be seen with a
microscope, and are held together at their centers by centromeres, giving the
chromosomes a configuration of an X. Each identical rod in a chromosome is called
a chromatid.
b. Centrioles replicate and pairs of centrioles, or centrosomes, move to opposite
sides of the nucleus.
c. Spindle fibers form a bridge between the ends of the cell.
d. The nuclear envelope begins to break down, and the nucleolus disappears.
2. Prometaphase (pro- “first,” meta- “change” & -phase “stage”)
a. The nuclear envelope dissolves.
b. Centrosomes have moved to the opposite poles of the cell.
c. Spindle fibers attach to the chromosomes at the centromeres.
3. Metaphase (meta- “change” & -phase “stage”)
a. Spindle fibers attach to the chromosomes at the centromere and align them along
the center of the cell, or metaphase plate. This alignment ensures each new
nucleus will have one correct set of chromosomes.
4. Anaphase (ana- “up” & -phase “stage”)
a. The spindle fibers separate the paired chromosomes at each centromere.
b. Each chromatid becomes a new chromosome.
c. Spindle fibers pull the new chromosomes to opposite sides of the cell.
5. Telophase (telo- “end” & -phase “stage”), is the final stage of cell division.
a. Chromatids are located at opposite ends of the cell.
b. Chromosomes begin to uncoil and lose their rod shaped appearance
c. Spindle fibers disperse.
d. A new nuclear membrane forms around each set of sister chromosomes, and the
nucleolus reforms.
e. The cytoplasm begins to pinch in at the center of the cell.
Stage Three of the Cell Cycle: Cytokinesis
Cytokinesis (cyto- “cell” & -kinesis “motion”) completes the process of cell division.
1. The cytoplasm divides.
2. The cell membrane encloses each, dividing the original cell in two.
3. The organelles are distributed into each of the new cells.
4. Each cell is referred to as a daughter cell. Each daughter cell should be genetically
identical.
5. At the end of cytokinesis, each cell enters interphase, and the cycle begins again.
Plant cell walls cannot squeeze together like an animal cell. A cell plate forms across the
middle of the cell. A new membrane forms between the new daughter cells, and then a new cell
wall forms around the cell membrane.
Cytokinesis in an animal cell:
Cytokinesis in a plant cell:
Mitosis
source: http://www.shmoop.com/dna/dna-replication.html
Mitosis
Name:_______________
_________
The Cell Cycle
1. Why does cell division need to happen?
2. Does cell division happen at the same rate in all cells?
Explain.
3. What are the three stages of the cell cycle (in order)?
a.
b.
c.
4. True/False: The cell cycle and cell division are the same thing. Justify your answer.
5. The process in which the DNA of a cell is copied in preparation for cell division is known
as _______________. This process occurs in ______________, the first
stage of cell division.
6. What are the five stages of mitosis?
a.
b.
c.
d.
e.
7. Genetic material can exist in the nucleus of the cell in two forms. _______________
is the de-condensed form of the genetic material. When the cell is preparing to divide, this
material condenses to form _______________. This occurs in
_______________, the first stage of mitosis.
8. In what stage of mitosis do chromosomes align at the center of the cell?
9. In what stage of mitosis does the nuclear envelope dissolve?
10. In what stage of mitosis does the mitotic spindle pull sister chromatids to opposite poles?
11. In what stage of mitosis does the nuclear envelope reform and cell division begins?
12. Two identical cells, known as ______________ cells, are formed in
_______________, the third and final stage of cell division.
13. The process of cytokinesis occurs when the ______________ begins to divide. It
starts to occur during _______________, the final stage of mitosis.
14. The _______________ forms across the middle of plant cells undergoing
cytokinesis.
Investigation: Mitosis in Cancer Cells
Purpose
1. To observe the stages and appearance of mitosis in healthy cells.
2. To compare mitosis in healthy cells vs. mitosis in cancer cells.
3. To determine what types of plants are most effective as cancer drugs.
Materials
• Photographs of whitefish blastula cells
• Information on cancer cells and mitosis in cancer cells
• Information on tropical plants an their affects
Pre-lab Questions:
(Please answer these questions before moving onto the procedure sections of the lab.)
1. Why is mitosis important for human body cells?
2. What would happen if mitosis didn’t occur at all in the human body?
3. In your own words, define cancer.
4. How do you think mitosis is involved in cancer?
5. How could medicines that change the rate of mitosis affect patients with cancer?
Procedure: Healthy Cell Mitosis
Obtain images of the whitefish blastula cells. Each image is magnified so that the cellular
structures can be observed.
1. Record your observations of the cell processes occurring in each of the following stages.
a. Interphase:
b. Prophase:
c. Metaphase:
d. Anaphase:
e. Telophase:
2. Prophase lasts significantly longer than the other stages of mitosis. What cell processes go
on in prophase that makes it last so much longer?
Procedure: Cancer Cell Mitosis
Cancer is a disease where mitosis does not occur properly. Mutations in the sequence of
DNA cause cell cycle genes to behave improperly. These cell cycle genes are no longer able to
control the rate of mitosis, and the mutated cancer cells undergo rapid mitosis—they divide out
of control, forming abnormal growths called tumors. While some types of tumors are harmless,
other types of tumors can cause serious health problems.
1. Does mitosis in cancer cells occur at a faster or slower rate than in normal cells?
2. If cancer cells continue to undergo mitosis without stopping, are they skipping any steps
in the cell cycle?
3. What would happen if abnormal mitosis continued in the body without being treated?
Procedure: Determining Natural Sources for Cancer Drugs
The information in the chart below shows types of plants and bacteria that are used in
medicine and science. Read about the characteristics and medicinal properties of these
organisms, and think about which of the three would be the best to treat cancer with. (Hint:
which of the organisms affects cell division in a way that reduces the number of cancer cells?)
Plant or Bacteria Type
Characteristics & Medicinal Properties
This type of bacteria is found worldwide and produces
Crown Gall Bacteria
proteins that affect cell replication. The crown gall
(Agrobacterium tumefaciens)
bacterium increases cell division in plant cells.
The rosy periwinkle is a plant that grows in Mexico &
Rosy periwinkle
Australia and produces pink flowers with five petals. It
(Catharanthus roseus)
prevents chromosomes from replicating by binding with
important proteins in the cells.
The foxglove is a plant that grows throughout North
Foxglove
America and produces bell-shaped purple flowers. It
(Digitalis purpurea)
reduces swellings in the arms, legs, and abdomen.
Conclusion
1. Which type of plant or bacteria do you think would make the best cancer medicine?
2. Why do you think that the drug made from this organism would work?
3. Will your cancer drug speed up or slow down mitosis in the cancer cells?
Name:_____________
Science Starters—Mitosis & the Cell Cycle
Day One
1. How many cells do you think there are in the human body?
2. Does on person have the same number of cells in his or her body at the same time? Why
or why not?
Day Two
1. Which of the following statements is true? (circle the correct answer)
a. The cell cycle consists of six stages.
b. The cell cycle consists of three stages.
c. The cell cycle consists of nine stages.
d. The cell cycle consists of twelve stages.
Day Three
List the five stages of mitosis:
1.
2.
3.
4.
5.
Day Four
1. What change to the cell occurs in anaphase? (circle the correct answer)
a. The cytoplasm begins to pinch at the center of the cell.
b. The mitotic spindle pulls sister chromatids to opposite poles.
c. The nuclear envelope dissolves.
d. The nuclear envelope re-forms.
Day Five
This is your Friday quiz. Please think carefully through your answers! (20 points total)
1. How is mitosis in cancer cells different than mitosis in healthy cells? (4 points)
2. List the three stages of the cell cycle (3 points) and briefly describe what happens in each
stage (9 points)
Stage of the Cell Cycle
Changes to the Cell at this Stage
3. What is the difference between chromatin and chromosomes? (4 points)
Prior Knowledge Assessment
Pre-Lesson PKA
1. Do you always have the same number of cells in your body?
2. Are those cells the same ones you were born with?
3. How do you think the body would make new cells?
4. If one cell could divide to form two cells, would those two cells be the same or different
from the original cell? Why?
5. What do you think cell division looks like?
6. What do you think this process is called?
7. How many steps do you think are in this process?
8. Do you think this process happens all the time? Does it happen at the same rate in all cells?
Other Notes:
Prior Knowledge Assessment
Post-Lesson PKA
1. Do you always have the same number of cells in your body?
2. Are those cells the same ones you were born with?
3. How do you think the body would make new cells?
4. If one cell could divide to form two cells, would those two cells be the same or different
from the original cell? Why?
5. What do you think cell division looks like?
6. What do you think this process is called?
7. How many steps do you think are in this process?
8. Do you think this process happen all the time? Does it happen at the same rate in all cells?
9. How do you think your ideas changed since learning about the cell cycle and mitosis in
class?
10. Do you think that the lesson was helpful in understanding how the cell cycle and mitosis
works?
Other Notes: