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Cell Cycle and Mitosis
Watch
how
the
cells
divide
in
the following
video
4.
3. For
To2.keep
the
reproduction
cell
sizes
small
of
unicellular
for
increased
organisms
efficiency
(like
To
heal/repair
tissue
For1.
multicellular
organisms
to grow in size
Why
do
cells
divide?
clip. What do you notice happening?
bacteria)
How many stages of cell division
do you see in this image?
Cell Cycle
The cell cycle
is the life
cycle of a cell
First, we
will look at
Interphase…
)
Interphase
•
•
•
Longest stage of cell
division (90% of cell cycle)
Nucleus is visible
3 sub-phases:
G1: Cell growth
S: DNA is copied (DNA
Replication)
G2: Organelles
copied/duplicated to
prepare for division.
)
How do you know these cells are in
Most of interphase?
these cells are
Intact Nucleus
in Interphase
How is DNA packaged
into chromosomes?
DNA coils around set of 4
histone proteins, creating
a “bead on a string” called
a nucleosome
The nucleosome coils
into structures called
chromatin
Chromatin supercoils =
chromosome!
Key Vocabulary
• DNA molecules are packaged
into chromosomes
.
– Human somatic cells (body
cells) have 46 chromosomes.
– Human gametes (sperm or eggs)
have 23 chromosomes.
• Chromosomes are made of a
material called chromatin
.
Key Vocabulary
DNA
• Chromatin is composed of proteins and _____
• It is supercoiled around proteins, called
histones
.
• Together the DNA and histone molecules
form bead-like structures called nucleosome
Key Vocabulary
• The chromosome is
duplicated (during S)
• Each duplicated
chromosome consists
of two sister
chromatids
.
• These are connected
by a centromere .
Preparing for Division
(G2 of interphase)
Late Interphase: G2
Centrosomes (with centriole pairs)
Nuclear membrane still visible
Nucleolus
Chromatin has been replicated
Mitosis (M Phase)
The M Phase consists of:
• Mitosis and Cytokinesis
Mitosis: the division of the nucleus
Cytokinesis: the division of the cytoplasm
Four Stages of Mitosis:
• Prophase
• Metaphase
• Anaphase
• Telophase
Preparing for Division
Late Interphase: G2
Early Spindle Apparatus
Prophase
Centromere
Nuclear
membrane
disappears
Chromosome consisting of two sister chromatids
becomes visible
Metaphase
Chromosomes line up at an
imaginary line between the
centrosomes at opposite ends
of the cell.
The spindle attaches to
the centromeres.
Anaphase
Spindles pull the
“daughter”
chromosomes appart
Telophase
Two nuclei become visible
In animal cells, a Cleavage
Furrow is visible
In plant cells, a cell plate is
now visible
Cytokinesis
The cytoplasm and
organelles divide.
Telophase & Cytokinesis
What’s the end product?
• Two identical daughter cells ready to start
the cycle again… or not.
• Some cells (like your nerve and muscle
cells) do not undergo division.
• For those that do (your skin and the lining
of your intestinal tract) how would you
know how quickly division takes place?
http://www.biology.arizona.edu/cell_bio/activities/cell
_cycle/01.html