Cell Cycle
Stages and division of cell
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ion__how_the_cell_cycle_works.html
1.
Which of the following represents the correct order of the phases of the cell cycle?
A)G1 -> G2 -> S -> M
Quiz
B)G1 -> G2 -> M -> S
C)G1 -> S -> G2 -> M
D)G1 -> S -> M -> G2
E)G1 -> M -> G2 -> S
2. The division of the cytoplasm is called
A)synapsis.B)mitosis.C)meiosis.D)cytokinesis.E)cytogenetics.
3. Which of the following represents the correct order of the phases of mitosis?
A)prophase -> anaphase -> metaphase -> telophase
B)prophase -> metaphase -> anaphase -> telophase
C)prophase -> metaphase -> telophase -> anaphase
D)metaphase -> prophase -> telophase -> anaphase
E)metaphase -> prophase -> anaphase -> telophase
4. DNA replication occurs in mitosis.A)TrueB)False
5. Mitosis and cytoplasmic division result in the formation of two genetically identical
Answers
1. C
 2. D
 3. B
 4. B
 5. A
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The cell cycle is an ordered set of events,
culminating in cell growth and division
into two daughter cells.
Non-dividing cells not considered to be
in the cell cycle.
Sequence of cell cycle is G1-S-G2-M. T
he G1 stage stands for "GAP 1". The S
stage stands for "Synthesis". This is the
stage when DNA replication occurs. The
G2 stage stands for "GAP 2". The M stage
stands for "mitosis", and is when nuclear
(chromosomes separate) and cytoplasmic
(cytokinesis) division occur. Mitosis is
further divided into 4 phases.
Regulation of Cell Cycle
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How cell division (and thus tissue growth) is controlled is very complex. The
following terms are some of the features that are important in regulation, and places
where errors can lead to cancer. Cancer is a disease where regulation of the cell
cycle goes awry and normal cell growth and behavior is lost.
Cdk (cyclin dependent kinase, adds phosphate to a protein), along with cyclins, are
major control switches for the cell cycle, causing the cell to move from G1 to S or
G2 to M.
MPF (Maturation Promoting Factor) includes the CdK and cyclins that triggers
progression through the cell cycle.
p53 is a protein that functions to block the cell cycle if the DNA is damaged. If the
damage is severe this protein can cause apoptosis (cell death).
p53 levels are increased in damaged cells. This allows time to repair DNA by blocking
the cell cycle.
A p53 mutation is the most frequent mutation leading to cancer. An extreme case of
this is Li Fraumeni syndrome, where a genetic a defect in p53 leads to a high
frequency of cancer in affected individuals.
p27 is a protein that binds to cyclin and cdk blocking entry into S phase. Recent
research (Nature Medicine 3, 152 (1997)) suggests that breast cancer prognosis is
determined by p27 levels. Reduced levels of p27 predict a poor outcome for breast
cancer patients.
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In mammalian cells, different Cyclin-CDK
(Cyclin-Dependent Kinases) complexes
are involved in regulating different cell
cycle transitions: Cyclin-D -CDK4/6 for
G1 progression, Cyclin-E -CDK2 for the
G1-S transition, Cyclin-A -CDK2 for Sphase progression, and Cyclin-A/B-CDC2
for entry into M-phase.