Download Inquiry into Life, Eleventh Edition

Chapter 5
Cell Division
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What’s the big idea?
Are ALL cells the same??
Do cells live forever?
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Types of Cells
• Somatic cells  body
cells
– 2n # of chromosomes
– Divide by mitosis
• Gametes  egg &
sperm cells
– 1n # of chromosomes
– Divide by meiosis
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Regulating # of cells
• Cell division
• Increases number of somatic cells
• Mitosis-division of nucleus
• Cytokinesis-division of cytoplasm
• Apoptosis
• Programmed cell death
• Prevents abnormal cells from
proliferating
• Enzyme-mediated
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Learning Target
4. Describe the events that occur in the
cell cycle.
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Cell Cycle
• Life cycle of cell  mitosis to
mitosis
• 3 parts  Interphase,
mitosis, cytokinesis
• Driven by enzymes (cyclins)
 buildup pushes cell past
checkpoints (G1, G2, M) 
cells divide
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Interphase
• Most of cell’s “life”
• Some cells
permanently
“stuck” in
Interphase (nerve,
muscle)
• Cell functions
continue as cell
prepares to divide
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Checkpoints
• Three checkpointsG1,
G2 & M
• Cyclin must be present
for stages to progress
• Govern whether a cell
progresses to next stage
– Default is to stop
unless overridden by
specific go ahead
signal
– Intracellular signals
detected by control
center determine if
key processes have
been completed
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Interphase
• G1 stage
– organelles
double in
number
– accumulates
materials needed
for division
– G1 checkpoint
• p53 stops cycle if
DNA damaged
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Interphase
• S stage
– DNA replication
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Chromosomes
• DNA replicates during “S”
remains connected at
centromere (Sister chromatids)
• Chromatin (DNA) wraps around
histones (protein “balls”)
• * DNA/histone “complex”
(nucleosome) supercoils 
chromosome
• Chromosomes-condensed rodshaped DNA molecules during
division
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Interphase
• G2 stage
– synthesis of
proteins needed for
division,
– double checks
growth &
replication
– G2 checkpoint
• stops cycle if DNA
is not done
replicating or is
damaged
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Learning check
• What would happen to the daughter
cells if the S phase of the Cell cycle
was removed?
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Learning Targets
5. Explain how the cell cycle is
controlled and what occurs when
control of the cycle is lost.
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Factors that affect cell division
• Growth factors
– Secreted by other cells,
stimulate division
– Over 50 different growth
factors
• Density dependent
inhibition
– Crowded cells stop
dividing because of
physical contact of
surface proteins
• Anchorage dependence
– Must be in contact with
solid surface to divide
(ECM)
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Learning Target
6. Recognize the type of daughter cells
formed through mitosis and their
chromosome number as compared to
the parent cell.
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Chromosome Number
• Each species has unique chromosome #
no relationship to complexity
• Diploid--2n  2 copies of each
chromosome (1/Mom & 1/Dad)
(Homologous pairs)
– All somatic cells (body cells) are 2n
• Haploid--1n  1 copy of each
chromosome (either Mom’s or Dad’s)
– Only gametes (sperm/eggs) are 1n
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Mitosis (Animal Cells)
• After “S” phase replicates DNA
• Division of nucleus ONLY !
chromosome # stays constant
• Centromere divides  each
chromatid becomes a daughter
chromosome
• M checkpoint-stops if
chromosomes not aligned
• Prophase
• Metaphase
• Anaphase
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• Telophase
Prophase
• 5 “events”  memorize them!
1. Chromatin coils 
chromosomes appear
2. Nucleolus disappears
3. Nuclear membrane
disappears
4. Centrioles & asters appear 
move to opposite poles of cell
5. Spindle fibers appear
1. Polar fibers  centriole to
centriole
2. Kinetochore fibers 
centriole to centromere
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Metaphase
• Kinetochore fibers
push chromosomes to
middle of cell
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Anaphase
• Kinetochore fibers
separate  break
centromeres  pull
chromatids to
opposite poles of cell
• Characteristic “V”
shape
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Telophase
• Reverse of Prophase
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Mitosis—Plant Cells
• Mitosis in plant cells
– Same phases as animal cells
– Plants don’t have centrioles or asters
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Cytokinesis
• Cytoplasm divides after
mitosis
• Animals  Cleavage
“furrow” (edges in)
• Plants  Cell Plate
(center out)
• Mitosis animation:
•
•
http://www.sumanasinc.com/webcontent/an
isamples/majorsbiology/mitosis.html
http://vcell.ndsu.edu/animations/mitosis/mo
vie-flash.htm
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Image found 11/29/4 on https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcT5zNgamn0R-M0Lufaxzvr5aXdjNYL1fb7lelcyz6w4Wwc7PEsTFQ
Mitosis in Prokaryotes
• Asexual reproduction
(Binary Fission) 
Cloning
• 2 identical daughter
cells
• Single DNA strand
duplicates  cell
elongates, pinches in
half
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Benefits of Mitosis
• Genetically identical
daughter cells
• Take advantage of
good conditions
rapidly
• Algal blooms
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