Team
Members:
Lab #5: Cell cycle and the continuity of life – how do cells reproduce?
Read the following information on chemotherapy and answer the questions below.
How Does Chemotherapy Work?
(from the American Cancer Society website www.cancer.org)
Chemotherapy is a distinctively different approach
than surgery and radiation therapy to treat cancer.
Rather than physically removing a tumor or a part of
it, chemotherapy uses chemical agents (anti-cancer
or cytotoxic drugs) to interact with cancer cells to
eradicate or control the growth of cancer. To
understand how chemotherapy works as a treatment,
it is helpful to understand the normal life cycle of a
cell in the body. All living tissue is composed of
cells. Cells grow and reproduce to replace cells lost
during injury or normal "wear and tear." The cell
cycle is a series of steps that both normal cells and
cancer cells go through in order to grow and
reproduce to form new cells. Understanding the cell
cycle can help doctors predict which drugs are likely
to work well together and how to decide how often
doses of each drug should be given.
Vinblastine and taxol are two drugs that inhibit the
correct formation of the mitotic spindle, therefore
inhibiting cell division. These drugs work during
the _______________ phase(s).
There are 5 phases in the cell cycle, designated by
letters and numbers:
G0 phase - Resting stage: Cells have not yet
started to divide. Cells spend much of their lives
in this phase. Depending on the type of cell, it
can last for a few hours to a few years. When the
cell is signaled to reproduce, it moves into the
G1 phase.
G1 phase - RNA and protein synthesis: During this
phase, the cell starts making more proteins to get
ready to divide.
S phase - DNA synthesis: In the S phase, the
chromosomes containing the genetic code
(DNA) are copied so that both of the new cells
formed will have the right amount of DNA.
G2 phase - Construction of mitotic spindle: The G2
phase is just before the cell starts splitting into
two cells.
M phase (mitosis): In this phase, which lasts only
30 to 60 minutes, the cell splits into 2 new cells.
Topoisomerase II inhibitors, such as topotecan and
VP-16, are drugs that interfere with DNA
replication. These drugs work during the
___________________ phase(s).
Antimetabolites (such as 5-fluorouracil,
capecitabine, 6-mercaptopurine, and methotrexate)
are a class of drugs that interfere with DNA and
RNA synthesis. These drugs work during the
________________ phase(s).
Hair follicles, skin, and the cells that line the
gastrointestinal tract are most sensitive to the
effects of chemotherapy. Explain why it is so.
What kind of side effects you might see in a patient
undergoing chemotherapy?
__________________________________
Figure 1. The cell cycle including
Interphase, Mitosis, and G0
_________________________________________
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Case Study. You are hired by a beer brewing company to find a strain of yeast that can ferment grains to ethanol
faster, so you need to find a fast growing yeast strain – the first step is to measure how fast their current yeast grows and
divides. To do this, you remove some of their yeast from the freezer (where they are all in G0) and add them to a warm,
sugary, malty wort. As they start to grow and divide, you remove a sample every two hours and count the number of
cells, and measure the amount of DNA and protein in each sample. Plot the data below. Be sure to label the axis.
You could make two separate graphs, one for DNA and one for protein, but to save space, plot them both on the same
grid (but use the left hand Y-axis for the DNA concentration and the right hand Y-axis for the protein concentration.
Time
(hours)
0
2
4
6
8
10
12
14
16
18
20
DNA
(picograms/cell)
0.90
1.04
1.20
1.19
1.20
0.60
0.61
0.59
0.62
0.74
0.89
Protein
(picograms/cell)
28.5
29.0
29.9
30.4
30.4
15.2
20.0
24.8
27.5
28.0
29.1
Time
(hours)
22
24
26
28
30
32
34
36
38
40
42
DNA
(picograms/cell)
1.06
1.2.0
1.21
1.2
0.6.0
0.61
0.58
0.62
0.74
0.90
1.06
Protein
(picograms/cell)
29.0
29.9
30.4
30.4
15.2
20.0
25.0
27.4
28.2
29.2
29.1
During which time period do you observe the most rapid increase in DNA? ________________
What phase of the cell cycle does this correspond to? Circle one: G1, S, G2, Mitosis, Cytokinesis
During which time period do you observe the most rapid increase in protein ______________
What phase of the cell cycle does this correspond to? Circle one: G1, S, G2, Mitosis, Cytokinesis
When did cytokinesis occur? _____ When did G2 occur? _____ When did Mitosis occur _____?
Use your answers to label on the graph when each phase occurred: G1, S, G2, Mitosis, Cytokinesis
How long did it take the cells to complete one cycle?
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Figure 3: Meiosis
Figure 2: Mitosis
Examine the onion root slide at 400X magnification – compare the cells from the tip of the
onion to the cells at the base of the onion root.
Do the various stages of interphase (G1 vs S vs G2) look different?
Yes or no?
Do the various stages of mitosis (prophase, metaphase, etc) look different?
Yes or no?
The onion root tip / base (circle one) has more cells undergoing mitosis. Explain why:
Which phase of the cell cycle is most frequent in the onion root tip?
interphase
prophase
metaphase
anaphase
telophase
cytokinesis
Which phase of the cell cycle is least frequent in the onion root tip?
interphase
prophase
metaphase
anaphase
telophase
cytokinesis
Explain why some mitotic phases are more frequently observed than other phases.
Observe the various stages of meiosis in the prepared slides of testes & ovaries from animals.
Compare Figure 2 and Figure 3:
How many daughter cells result when one cell completes mitosis? ________________
How many daughter cells result after one cell completes meiosis?
________________
What is the difference between a somatic cell and a germ cell: Give two examples of each
within humans. How many chromosomes are in each of your examples?
Germ cells
example
# of
chromosomes
Somatic cells
example
# of
chromosomes
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Why is it necessary for gametes (also known as ‘germ cells’) to be haploid?
Explain “crossing over” in the context of meiosis. Describe how crossing over during the
creation of germ cells can benefit the organism.
At what time in your life will your body be undergoing the most cell division, and hence the time
when good nutrition is most important and when toxins have the greatest impact?
What is the general term for when the controls for mitosis fail and cells divide more often than
they are supposed to?
What causes the regulation of mitosis to fail in some cells, but not others?
List three things that increase the risk of a genetic change that leads to the misregulation of mitosis.
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