The Cell Cycle 11 October, 2002 Text Chapter 12

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The Cell Cycle11 October, 2002Text Chapter 12
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Cell division functions in reproduction, growth,
and repair
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Important Terms (part one)
genome all of a cells DNA
chromosome individual DNA molecule
chromatin chromosomal DNA and its protein
scaffold
sister chromatids the two identical copies of
a duplicated chromosome
centromere the point of attachment for two
sister chromatids
somatic cells (most cells) have two copies of
each chromosome (diploid)
gametes (reproductive cells sperm and eggs)
have one copy of each chromosome (haploid)
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More Important Terms
cell cycle the process of cell division
mitosis (M phase) nuclear division
interphase the main part of the cell
cycle
G1 phase - cell prepares for DNA synthesis,
usually grows in size
S phase - DNA is duplicated
G2 phase - cell checks fidelity of DNA
replication, prepares for nuclear division
mitosis subphases - prophase, prometaphase,
metaphase, anaphase, telophase
cytokinesis
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Mitosis (1)
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Mitosis (2)
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The Mitotic Spindle
The mitotic spindle is composed of microtubules,
and directs the alignment of chromosomes on the
metaphase plate.
During anaphase, the microtubules attached to
each centromere guide the movement of chromosomes
toward spindle poles.
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Polar Depolymerization of Microtubules
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Cytoplasmic Division
Microfilaments contract to divide the cytoplasm.
Plant cells are less flexible, because of the
cell wall, and deposit cell wall material between
the two daughter cells.
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Mitosis (differential staining)
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Mitosis in Growing Tissue
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Binary Fission in Bacteria
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Evolution of Mitosis
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Cell Cycle Control
The cells place in the cell cycle is signaled by
the presence or absence of cell cycle kinases.
A growth signal leads to passage through the G0
restriction point into G1. (See Fig 11.11)
The cell then executes a programmed series of
steps that culminate in mitosis and cytokinesis.
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MPF
is an example of kinase control of the
cell cycle. It is like a license that allows the
cell to begin M phase of the cell cycle.
MPF is a two-subunit enzyme. One subunit is Cdk
(present during the whole cell cycle). The other
subunit is a cyclin protein that builds up as M
phase approaches.
When the cyclin concentration is high enough,
cyclin binds to Cdk, forming the MPF enzyme. MPF
activity signals the start of mitosis.
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Cancer
Normal cells are transformed to tumor cells when
cell division is not controlled.
Cancer cells are growth-factor independent.
Cancer cells have escaped density-dependent
inhibition.
Most cancerous cells are destroyed by the immune
system, but some cells progress from benign to
malignant, and possibly to metastatic.
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Cell Culture and Growth Factors
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Density-dependent Inhibition
Density-dependent inhibition is a property of
normal cells.
Cancer cells lack this inhibition.
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Metastatic Cancer
Metastatic cancer cells spread throughout the
body.
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