AP Biology
Unit 2 – Cells AP Lab 7
One of the characteristics of living things is the ability to replicate and pass
on genetic information to the next generation. Cell division in individual bacteria
and archaea usually occurs by binary fission. Mitochondria and chloroplasts also
replicate by binary fission, which is evidence of the evolutionary relationship
between these organelles and prokaryotes.
Cell division in eukaryotes is more complex. It requires the cell to manage a
complicated process of duplicating the nucleus, other organelles, and multiple
chromosomes. This process, called the cell cycle, is divided into three parts:
interphase, mitosis, and cytokinesis. In the first growth phase (G1), the cell grows
and prepares to duplicate its DNA. In the synthesis phase (S), the chromosomes
are replicated. In the second growth phase (G2), the cell prepares to divide. In
mitosis, the duplicated chromosomes are separated into two nuclei. In most cases,
mitosis is followed by cytokinesis, when the cytoplasm divides and organelles
separate into daughter cells. This type
of cell division is asexual and is
important for growth, renewal, and
repair of multicellular organisms.
Cell division is tightly controlled by
complexes made of several specific
proteins.
These complexes contain enzymes
called cyclin-dependent kinases
(CDKs), which turn on or off the
various processes that take place in
cell division. CDK partners with a
family of proteins called cyclins. One
such complex is mitosis-promoting
factor (MPF), sometimes called
maturation-promoting factor, which
contains cyclin A or B and cyclindependent kinase (CDK). (See Figure
1a.) CDK is activated when it is bound
to cyclin, interacting with various
other proteins that, in this case, allow
the cell to proceed from G2 into
mitosis. The levels of cyclin change
during the cell cycle (Figure 1b). In most cases, cytokinesis follows mitosis.
AP Lab 7 Mitosis.docx (portions adapted from API Lab 7)
Greg Ballog 2015
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As shown in Figure 2, different CDKs are produced during the phases. The cyclins
determine which processes in cell division are turned on or off and in what order
by CDK. As each cyclin is turned on or off, CDK causes the cell to progress
through the stages in the cell cycle.
Cyclins and CDKs do not allow the cell to progress through its cycle
automatically. There are three checkpoints a cell must pass through: the G1
checkpoint, G2 checkpoint, and the M-spindle checkpoint. At each of the
checkpoints, the cell checks that it has completed all of the tasks needed and is
ready to proceed to the next step in its cycle. Cells pass the G1 checkpoint when
they are stimulated by appropriate external growth factors; for example, plateletderived growth factor (PDGF) stimulates cells near a wound to divide so that they
can repair the injury. The G2 checkpoint checks for damage after DNA is
replicated, and if there is damage, it prevents the cell from going into mitosis. The
M-spindle (metaphase) checkpoint assures that the mitotic spindles or
microtubules are properly attached to the kinetochores (anchor sites on the
chromosomes). If the spindles are not anchored properly, the cell does not
continue on through mitosis. The cell cycle is regulated very precisely.
Mutations in cell cycle genes that interfere with proper cell cycle control are found
very often in cancer cells.
Figure 3
illustrates how the
chromosomes
move during
mitosis. It is
important to
model how the
duplicated
chromosomes
align, separate,
and move into
new cells.
AP Lab 7 Mitosis.docx (portions adapted from API Lab 7)
Greg Ballog 2015
Page 2 of 6
Protocol
A
ctivity 1 - Cell Cycle
Step 1 ) In this step you will explore the different phases of the cell cycle. Use the
web site: http://www.biology.arizona.edu/cell_bio/tutorials/cell_cycle/cells2.html to
help you complete the diagram of the cell cycle. Label all components and provide a
description of each.
Cell Cycle
G0
G1
S
G2
A
ctivity 2 Phases of Mitosis
Step 2) In this step you will explore the different phases of mitosis. Use the web site:
http://www.biology.arizona.edu/cell_bio/tutorials/cell_cycle/cells3.html. Complete this
before going on to step 3.
Drawing
Phase Name
Description
InterPhase
ProPhase
AP Lab 7 Mitosis.docx (portions adapted from API Lab 7)
Greg Ballog 2015
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MetaPhase
AnaPhase
TeloPhase
Step 3) In this step you will observe mitosis in onion root tips. The web site:
www.biology.arizona.edu/cell_bio/activities/cell_cycle/assignment.html is essential to
completion of this step. You will notice that the cells are small and a bit unclear, this is to
mimic what you will actually see under the microscope. Complete this before going on to
step 4.
Step 4) In this step you will be looking at slides of onion root tips for the various phases
of the cell cycle. Each slide will have all stages of mitosis present because the cells
replicate at different times. Make a drawing in your lab journal of each phase as you
locate them. Have Mr. Ballog verify your identification and stamp each drawing .
Lab Questions
1) What is the collective name for G0, G1, S, and G2 phases?
2) What is the overall purpose of mitosis?
3) How many cells are there at the end of the mitosis of one cell?
AP Lab 7 Mitosis.docx (portions adapted from API Lab 7)
Greg Ballog 2015
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4) Why weren’t the drawings on the practice web site larger and clearer?
5) Why are all of the stages present in each root section?
6) What are chromosomes made of?
7) Why is the prepared slide from an onion root tip?
8) What is the best magnification for observation of mitosis?
9) Cancer is associated with rapid cell division. Which stage, if any, would you expect
might be missing in a slide of cancerous cells? Explain.
Step 5) In this step you will take data from several microscope fields of root tip slides.
Observe every cell in one high power field of view and determine which phase of the
cell cycle it is in. This is best done in pairs. The partner observing the slide calls out the
phase of each cell while the other partner records. Then switch so the recorder becomes
the observer and vice versa. Count at least two full fields of view. If you have not
counted at least 200 cells, then count a third field of view.
Number of Cells
Field 1
Field 2
Percent TIme In
of
Each Stage
Total
Cells
Counted
Field 3
Total
lnterphase
Prophase
Metaphase
Anaphase
Telophase
Total Cells Counted
Calculate the percentage of cells in each phase.
Consider that it takes, on average, 24 hours (or 1,440 minutes) for onion root-tip cells to
complete the cell cycle. You can calculate the amount of time spent in each phase of the
cell cycle from the percent of cells in that stage.
Percent of cells in stage X 1,440 minutes = __________ minutes of cell cycle spent in stage
Step 6) In this step you will analyze data taken from plants induced to divide abnormally.
Scientists reported that a fungal pathogen may affect the growth of soybeans. The
soybean growth was decreased during three years of high rainfall. The soybean roots
were poorly developed. Close relatives of R. anaerobisare plant pathogens grow in the
soil. A lectin-like protein, which may be secreted by the fungus, was also found in soil
surrounding the soybean roots. Lectins accelerate mitosis in some root apical meristems.
In many instances, rapid cell division weakens plant tissues causing reduced overall
survival and production.
The following data was obtained by observing a control group of normal root cells and an
experimental group of cells exposed to lectin.
AP Lab 7 Mitosis.docx (portions adapted from API Lab 7)
Greg Ballog 2015
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Perform a chi-square analysis to determine if there is support for the hypothesis that
lectin is the causal agent for the soybean parthenogenesis. Record all calculations in your
lab journal.
Step 7) In this step you will briefly research the abnormal cell cycle disease commonly
known as cancer. Cancer is a disease that is triggered by abnormal cell division. In order
for a tumor to develop a number of changes must occur to the DNA in the cell. Go to the
website;
http://www.insidecancer.org/
then watch all parts of the Hallmarks of Cancer tutorial. Use the information from the
website to describe, in your journal, each of the ‘Hallmarks of Cancer’ listed below.
Uncontrolled growth –
Evading death –
Processing nutrients –
Becoming immortalInvading tissues –
Avoiding detection –
Promoting mutations The following site has a good overview of the in-vitro cell line most used to study cancer.
http://berkeleysciencereview.com/article/good-bad-hela/. Compare the normal karyotype
with the HeLa karyoptype. Discuss what may have happened during the cell cycle to
allow the observed abnormalities. If available we will perform a “cell splat” of HeLa
cells. Draw a representative set of chromosomes if you are able to perform the HeLa cell
splat.
Normal karyoptype
AP Lab 7 Mitosis.docx (portions adapted from API Lab 7)
HeLa karyotype
Greg Ballog 2015
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