Download Cell Cycle Multiples Cells

Section 9.2
 Your genetic material exists as a mass of very long fibers
that are too thin to be seen under a light microscope.
These fibers consist of chromatin, a combination of DNA
and protein molecules.
 When the cell prepares to divide, chromatin fibers
condense, becoming visible as the compact structures
called chromosomes.
 The cell duplicates all of its chromosomes before
cell division. These 2 identical joined copies are
called sister chromatids.
 The region where the two chromatids are joined
tightly together is called the centromere.
 Eukaryotic cells that do
divide undergo an
orderly sequence of
events known as the
cell cycle.
 The cell cycle extends
from the "birth" of a
cell as a result of cell
reproduction to the
time the cell itself
reproduces.
 (Figure 9-5)
 Interphase
 Consists of 3 smaller phases:
 G1
 S
 G2
 Mitotic Phase
 Consists of 2 smaller phases :
 Mitosis
 Cytokinesis
 The cell may spend as much as 90 percent of the cell cycle
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in Interphase.
Interphase is the stage during which a cell carries out its
metabolic processes and performs its functions.
One key event is the duplication of the DNA in the cell's
chromosomes. This period is called the S phase (S stands
for DNA synthesis).
The interphase periods before and after the S phase are
called the G1 and G2 phases (G stands for gap). During the
G2 phase, each duplicated chromosome remains loosely
packed as chromatin fibers.
The cell is now ready to begin mitosis.
 The stage of the cell cycle
when the cell is actually
dividing is called the
mitotic phase (M phase).
 During mitosis, the
nucleus and the duplicated
chromosomes divide and
are evenly distributed,
forming two "daughter"
nuclei.
 Cytokinesis is the process
by which the cytoplasm is
divided in two.
 The combination of mitosis and cytokinesis
produces two genetically identical daughter
cells since the chromosomes were duplicated
precisely in the S phase.
 Each daughter cell has a single nucleus, some
surrounding cytoplasm, and a plasma
membrane.
 Mitosis is a very accurate way of distributing
identical copies of a large amount of genetic
material to two daughter cells.
 Mitosis is unique to eukaryotes.
1.
Describe how the appearance of chromosomes
changes as a cell is about to divide.
2.
Interphase used to be described as a "resting phase."
Why is this description inaccurate?
3.
Summarize the events that occur during mitosis and
cytokinesis.