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Chapter 12 The Cell Cycle –Study Guide ANSWERS
12.1 Cell division basics____________________________________________________
1. True or False: Chromosomes are made of DNA only. If false, correct the statement
False, chromosomes are made of DNA and associated proteins. DNA is wrapped around
these proteins. The DNA is packaged in the nucleus by wrapping it around proteins.
2. Each chromosome contains many ____Genes__________, which are segments of the
chromosome that codes for a certain polypeptide (protein).
3A. In what stages of the cell cycle are chromosomes visible under the microscope?
The chromosomes become visible during prophase and remain visible through mitosis
(prophase metaphase anaphase telophase) and begin to de-condense during
telophase of mitosis.
B. Why are they visible during these stages?
Chromosomes duplicate and condense during prophase of mitosis making them visible
under a microscope. They condense in order to more easily distribute the correct amount
of DNA into each daughter cell.
4. Explain the basic differences between Mitosis and Meiosis. Name a cell type that
undergoes Mitosis. Name a cell type that undergoes Meiosis.
Mitosis = results in two identical daughter cells ex: skin cell
Meiosis = results in four non-identical haploid cells ex: cells in gonads
5. Starting with a fertilized egg (zygote), a series of four mitotic cell divisions would
produce an early embryo with how many cells?
1 cell  2 cells  4 cells 8 cells 16 cells
Each arrow represents a mitotic cell division
6A.What is the name given to the duplicated chromatids of a chromosome when they are
still attached to one another during the first half of mitosis?
sister chromatids
6B. What are these chromatids called after they split during anaphase of mitosis?
Chromosomes
12.2 Mitotic phases________________________________________________________
7. Specific events occur during interphase to prepare the cell for Mitosis. Interphase is
divided into 3 sub-phases. Name each sub-phase and describe the events that occur
during each sub-phase.
G (Growth) 1= growth, manufacture organelles and proteins
S (synthesis) phase= Chromosome duplicate
G (Growth) 2 = growth, manufacture organelles and proteins
8. List (in order) starting with Interphase, the 5 phases of the cell cycle and give a brief
description of the major events that occur in each phase. (Use the powerpoint slides as a
guide for the amount of detail you need to know about each stage)
InterphaseG (Growth) 1= growth, manufacture organelles and proteins
S (synthesis) phase= Chromosome duplicate
G (Growth) 2 = growth, manufacture organelles and proteins
Prophase
-Duplicated Chromosomes appear as 2 sister chromatids connected at the centromere
-Mitotic spindle forms in cytoplasm from centrosomes
Metaphase
-Mitotic spindle fully formed
-Duplicated Chromosomes line up on metaphase plate located in middle of the cell
-Each sister chromatid is attached to a spindle fiber
Anaphase
-Sister chromatids are pulled apart and taken to opposite poles of the cell by the
spindle fibers
-Cell elongates
Telophase
-Roughly opposite prophase:
-Nuclear envelopes begin to reform around chromosomes
-Chromosomes begin to uncoil
-Mitotic spindle disappears
-Mitosis complete!
9. The average human cell can complete the cell cycle in approximately 24hrs. The cell
spends most of its time in one phase of the cell cycle. Identify this phase and explain why
so much time is spent in this phase.
Interphase- Much needs to be accomplished before a cell can divide. The cell spends
nearly the entire cell cycle in interphase for this reason.
Interphase events:
G (Growth) 1= growth, manufacture organelles and proteins
S (synthesis) phase= Chromosome duplicate
G (Growth) 2 = growth, manufacture organelles and proteins
10. Identify the function of centrosomes in mitosis.
Located outside nucleus, microtubules extend from centrosomes to form the spindle
11. A spindle is considered complete when…? (i.e. What major events must
occur/structures form?)
Spindle microtubules are attached to sister chromatids, asters extend from centrosomes
attaching to cell membrane
12. We discussed an experiment that explained how the chromosomes move to opposite
poles of the dividing cell during anaphase. Two hypothesis were made:
Hypothesis #1:chromosomes are pulled to the poles: spindle fibers shorten at their
spindle pole (centrosome) ends. The spindle fiber pulls the chromosome to the spindle
pole, like a horse (chromosome) being lassoed by a rope (spindle fiber).
Hypothesis #2: chromosomes walk to the spindle poles: spindle fibers shorten at their
kinetochore (part of chromosome that is attached to the spindle fiber) ends. The
chromosome “walks down” the spindle fiber and the spindle fiber dismantles behind the
chromosome.
A. Describe this experimental design and the experimental results.
Experimental Design: The spindle was tagged with a fluorecent marker. Florecence was
then removed from a specific region of the splindle at time A. (the spindle fibers in this
region were still present, only the fluorecent tag was removed). Mitosis proceeded and
another picture was taken at a later time B. The two pictures were then compared. The
region of the spindle where the fluorescence had been removed had not moved, but the
chromosome attached to the spindle fiber had moved closer to the spindle pole. This tells
us that the spindle fiber was shortening (dismantling) at the kinetichore (chromosome)
end and not the spindle pole (centrosome) end. If the region of the spindle where the
fluorescence had been removed had moved closer to the spindle pole at time B compared
to time A, then we would have concluded that the spindle fiber was shortening
(dismantling) at the spindle pole (centrosome) end
B. Which hypothesis was accepted? #2
13A. Define: Cytokinesis (Hint: break this word down into “cyto” and “kinesis”…what
do these words mean?)
Cyto- as in “Cytoplasm”
Kinesis- means “ to cut”
Cytoplasm cutting!
13B. How do the processes of Mitosis and Cytokinesis differ?
Mitosis = duplicate chromosomes
Cytokinesis = divide cell into two daughter cells
13C. How does cytokinesis in animal cells and plants cells differ?
Animal- microfilaments form ring around center of dividing cell and contract to form two
new cells
Plant- golgi vesicles containing cell wall material migrate to center of dividing cell to
form cell plate
14A. Prokaryotes reproduce by a process called ____binary fission___________.
14B. Describe the process of prokaryote cell division using the following terms:
origin of replication, genome replication, cell elongation, cell division (cytokinesis)
1. Origin of replication is duplicated
2. One copy of origin of replication moves to opposite end of cell
3. Genome Replication
4. Cell elongates
5. Cell divides
15. List at least 1 structural similarity and at least 2 structural differences between
bacterial (prokaryotic) chromosomes and eukaryotic chromosomes
Structural Similarities:
Both are made of DNA and associated proteins
Structural Differences:
Eukaryotic chromosomes are linear, many chromosome are present in a nucleus.
Prokaryotic chromosome circular, single chromosome NOT surrounded by nucleus
16. List at least 1 functional similarity and at least 1 functional difference between
bacterial (prokaryotic) chromosome and eukaryotic chromosome behavior during cell
division.
Functional Similarities:
Both duplicate their DNA before the cell divides
Both divide into two cells
Functional Differences:
Eukaryotic chromosomes move to opposite poles of cell by spindle fibers
Prokaryotic chromosome do not use spindle to move to opposite poles of the cell
12.3 Cell Cycle Regulation__________________________________________________
17. Name the three checkpoints in the cell cycle. How do they function (in general) to
control the cell cycle?
G1, G2, M
The cell must have certain molecules available in certain quantities in order to pass the
checkpoint and proceed to the next stage of the cell cycle.
18. What molecules control the G2 Checkpoint?
Cyclin dependent kinase (cdk) and cyclin. When the two molecules join it is called MPFMaturation Promoting Factor
19. How do cyclins and Cdk’s interact to control the G2 checkpoint?
Cdk’s are present throughout the cell cycle, whereas cyclins accumulate just before the
G2 checkpoint. Cdk’s are inactive without cyclins. If MPF (the cdk-cyclin complex) is
not present before the G2 checkpoint, the cell cycle will not proceed. The cell will be
held in Interphase and not permitted to enter the Mitotic phases of the cell cycle.
20A. According to the graph in the figure below, MPF activity reaches its highest
concentration at what stage in the cell cycle?
MPF concentration sharply increases just before the mitotic phases of the cell cycle and
reaches its highest point during the mitotic phases.
20B. How does this correlate with MPF’s functions during that stage in the cell cycle?
MPF phsophorylates (activates) proteins/molecules that have a role in the events of
mitosis. As a result, it is found in highest concentration during this phase of the cell
cycle!
Some events of Mitosis that MPF facilitates: dismantling the nuclear membrane, building
the spindle, sister chromatids walking down the spindle fiber to the cell pole, etc.
21A. Describe how Platelet Derived Growth Factor (PDGF) controls the cell cycle of
fibro.
PDGF is released from Platelets in the area of an injury. (Platelets are a type of blood cell
present in the blood stream. They also have a role in blood clotting.) PDGF binds to
fibroblast cells (connective tissue cells) at the site of the injury, which causes these cells
to divide. This will allow the injured tissue to eventually heal.
21B. Is this control present in cancer cells? Why/Why not?
No. Cancer cells do not respond to normal cell cycle signals
22. Distinguish among benign, malignant and metastatic tumors.
Benign = cancer cells localized to one part of an organ or tissue. The cells are tightly
bound to one another. Due to its structure, this type of tumor is more easily removed
compared to the other tumor types
Malignant = cancer cells that have spread throughout the tissues of an organ. The tumor
cells are no longer tightly bound to one another. The cancer cells can and usually impair
organ function.
Metastatic = cancer cells break-off from malignant tumor and flow through blood to
another area of the body. This can and usually does lead to the formation of secondary
tumors in other parts of the body.