MITOSIS LAB
AP BIOLOGY
DR WEINER
I. Mitosis
Background
All living things have the ability to reproduce and pass on their genetic information to offspring.
In prokaryotes, the reproduction occurs by a process called binary fission. In binary fission, the cell
grows, DNA is replicated, and the cell divides producing two identical cells.
In most eukaryotic cells, cell division involves a more complex process due to the fact that
eukaryotic cells have a nucleus and often multiple chromosomes. As in prokaryotes, eukaryotic cells
must grow to the maximal size before initiating cell division, and the DNA must be replicated. But in
order to ensure that the daughter cells produced are identical, a more complex series of steps must occur.
The cell must first carefully and precisely divide the nucleus into two identical nuclei, each with
identical copies of the chromosomes, before the cell itself can divide. The division of the nucleus is
called mitosis and involves several stages that ensure the chromosomes are equally distributed to the two
daughter cells. The actual splitting of the cell is called cytokinesis.
Cell division by mitosis usually results in the production of somatic (nonsex) cells. It is used for
growth, regeneration of body parts in lower vertebrates, and repair of damaged cells in multicelled
organisms. It is critical that the cells produced by mitosis are identical, therefore any mistakes must be
either corrected or mitosis must be aborted.
In order for mitosis to occur in a normal cell, the cell must pass through several checkpoints.
G1 checkpoint: check for cell size, proper environment, presence of growth factors, damaged DNA. If
this checkpoint fails then cell will enter Go arrest till conditions are optimal.
G2 checkpoint: check for precise DNA replication, DNA damage. If this checkpoint fails cell undergoes
apoptosis
M checkpoint: check for correct attachment of spindle s to chromosomes. If this checkpoint fails the cell
undergoes apoptosis
In order for each checkpoint to pass there has to be a specific cyclin/cyclin dependent kinase
(Cdk) complex that stimulates passage through that checkpoint. For example, growth factors bind to
cell surface receptors on cells. This binding initiates a cascade of events inside the cell that leads to the
transcription and translation of the cyclin present in the G1 phase. As the concentration of these
particular cyclins increase, they bind to their Cdks forming a complex that allows the cell to exit Go and
return to G1 to prepare for mitosis. These cyclin Cdk complexes will cause the release of tumor
suppressor proteins from specific transcription factors allowing the transcription of genes needed for cell
division to be produced.
Part I. Modeling Mitosis
Using the chromosome bead set, walk through the process of mitosis from interphase through
cytokinesis.
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Interphase: copy the chromosomes
Prophase: attach the spindles to both centromeres
Metaphase: align the chromosomes in the center of the cell
Anaphase: separate the sisters by pulling on the spindles
Telophase and cytokinesis: divide the cell
Circle the mitotic cells in both pictures:
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What is the main difference between the two pictures?
Which one is the phenoxy herbicide treated sample? Explain
Part II. Effect of phenoxy herbicides on mitosis
Hypothesis on the effect of phenoxy herbicides on mitosis:
Scientists obtained the following data on the effects of phenoxy herbicides on mitosis
Table I: Normal root tips
Interphase
cells
Mitotic cells
Total cells
SAMPLE 1
SAMPLE 2
SAMPLE 3
35
375
39
422
38
357
MEAN
STANDARD
DEVIATION
PERCENT
Table 2: phenoxy herbicide treated root tips
SAMPLE 1
Interphase cells
Mitotic cells
75
Total cells
427
SAMPLE 2
SAMPLE 3
93
419
70
373
MEAN
Complete the tables
Statistical analysis on the effect of phenoxy herbicides
What is your null hypothesis?
Complete the table
o
e
interphase
mitosis
Χ2 =
Degrees of freedom =
Critical value at p = 0.05 =
Do you accept or reject null hypothesis? Explain
(o-e)2/e
STANDARD
DEVIATION
Part III. Cancer and the Cell cycle
Cell division is regulated by two basic mechanisms, stimulation of cell division and inhibition.
Cell cycle inhibitory genes are called tumor suppressor genes and code for proteins that inhibit cell
division. They prevent the cell from progressing through the cell cycle. Two examples of tumor
suppressor genes are p53 and Rb. Cell cycle stimulatory genes are called proto-oncogenes and they
code for proteins such as transcription factors that are needed to transcribe genes involved in cell
division. Mutations in both genes can result in cancer. The genes involved in monitoring DNA damage
can also be mutated such that DNA damage is not repaired.
1. Examine the normal cell and the HeLa cells and determine the differences. Write it next to the
karyotypes
Normal cell:
HeLa cell:
1. Examine the normal and CML karyotype to determine where the differences are. Write it next to the
karyotypes
Karyotype of a female with chronic myelogenous leukemia
Karyotype of a normal female
Mitosis Lab Questions
1. How is the cell cycle controlled in normal cells?
2. What goes wrong with the cell cycle in cancer?
3. What happens to a normal cell if the DNA is damaged?
4. What is aneuploidy? HeLa cells are aneuploid. How might this lead to cancer?
5. What are Philadelphia chromosomes and how can they lead to cancer?
6. Why might the increased mitotic rate have caused the phenoxy treated plants to die?