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7
The Cell Cycle
and Cell
Division
Chapter 7 The Cell Cycle and Cell Division
Key Concepts
• 7.2 Binary Fission and Mitosis
• 7.3 Cell Reproduction Control
Two types of Reproduction
Asexual Reproduction
•Faster
•Creates genetically
identical cells (clones)
•Common in nature
•Only 1 parent is involved
•Examples: binary fission in
prokaryotes and mitosis in
eukaryotes
Sexual Reproduction
•Creates gametes (sex cells
– sperm and egg cells)
•Product has genetic
diversity
•2 parents are involved
•Examples - meiosis
Asexual Reproduction on a Large Scale
Sexual Reproduction on a big scale
Basic Term - Chromosome
• Consist of DNA and protein
• 3 forms
• Chromatin – 1 long strand, wrapped around
histones
• Chromatid – half of a chromosome
• Chromosome – full X, 2 sister chromatids held
together by a centromere
• Contain specialized proteins called
kinetochores
• Homologous Chromosomes – in pairs, similar in
shape, size and information (1 from Mom and 1
from Dad) - TETRAD
Basic Term - Chromosome
Figure 7.5 The Phases of the Eukaryotic Cell Cycle (Part 1)
Two kinds of Cells
Diploid Cells
•Chromosomes are in pairs
•Abbreviated 2n
•Example – Somatic (body)
cells, zygote
•Humans diploid # = 46
Haploid Cells
•Chromosomes are not in
pairs
•Abbreviated 1n
•Example – Gametes/Sex
Cells/Sperm/Egg/Spores
•Human haploid # = 23
Karyotype of Homo sapiens
Mitotic (doubled)
chromosomes taken from
a white blood cell at
metaphase
23 chromosome pairs, 46
total
Stained with Giemsa stain
to reveal differences in the
DNA/protein associations.
 Banding distinctive to
each chromosome
What was the sex of this
individual?
For any cell to divide
Four events must occur for cell division:
• Reproductive signal—to initiate cell division
• Replication of DNA
• Segregation—distribution of the DNA into the
two new cells
• Cytokinesis—division of the cytoplasm and
separation of the two new cells
Concept 7.2 Both Binary Fission and Mitosis Produce Genetically
Identical Cells
In prokaryotes, cell division results
in reproduction of the entire
organism.
The cell:
• Grows in size
• Replicates its DNA
• Separates the DNA and
cytoplasm into two cells through
binary fission
Cell Cycle
•5 parts
1.G1 - growth
2.S – DNA Synthesis
3.G2 – prepare for
mitosis
4.M – mitosis (PMAT)
5.C – Cytokinesis –
division of the
cytoplasm
Interphase
Interphase
• 3 parts – G1,S,G2
• Nucleolus and Nuclear
Membrane is Visible
• Longest phase of the
cell cycle
• Chromatin is visible
Figure 7.5 The Phases of the Eukaryotic Cell Cycle (Part 2)
Prophase
• 1st stage of mitosis
• Chromatin  chromosomes
• Centrosome and spindle
fibers are visible and start to
organize and move to
opposite poles
• Pair of centrioles
• Nuclear Membrane and
Nucleolus disappear
Metaphase
• 2nd stage of mitosis
• Chromosomes are
lined up at the
equator of the cell,
connected to the
spindle fibers by their
centromere
Anaphase
• 3rd phase in mitosis
• Chromosomes 
chromatids
• Spindle fibers pull
the chromosomes
apart and move
them towards
opposite poles
Telophase
• Last phase of
mitosis
• Chromatids 
chromatin (less
compact)
• Nuclear membrane
and nucleolus return
• Overlaps with
Cytokinesis
Cytokinesis
• After Interphase
• Division of the
cytoplasm (cleavage
furrow vs. cell plate)
• Each daughter cell
contains an exact
copy of DNA and are
identical in every
way
Figure 7.6 The Phases of Mitosis (1)
Figure 7.6 The Phases of Mitosis (2)
Concept 7.3 Cell Reproduction Is Under Precise Control
• The reproductive rates of most prokaryotes
respond to environmental conditions.
• In eukaryotes, cell division is related to the
needs of the entire organism.
• Cells divide in response to extracellular signals,
like growth factors.
Concept 7.3 Cell Reproduction Is Under Precise Control
• Progression is
tightly regulated—
the G1-S
transition is called
R, the restriction
point.
• Passing this point
usually means the
cell will proceed
with the cell cycle
and divide.
Concept 7.3 Cell Reproduction Is Under Precise Control
• Specific signals trigger the transition from one
phase to another.
• Transitions also depend on activation of cyclindependent kinases (Cdk’s).
• A protein kinase is an enzyme that catalyzes
phosphorylation from ATP to a protein.
• Phosphorylation changes the shape and
function of a protein by changing its charges.
Concept 7.3 Cell Reproduction Is Under Precise Control
Cdk is activated by binding to cyclin (by
allosteric regulation); this alters its shape and
exposes its active site.
The G1-S cyclin-Cdk complex acts as a protein
kinase and triggers transition from G1 to S.
Other cyclin-Cdk’s act at different stages of the
cell cycle, called cell cycle checkpoints.
Figure 7.10 Cyclins Are Transient in the Cell Cycle
Concept 7.3 Cell Reproduction Is Under Precise Control
Example of G1-S cyclin-Cdk regulation:
Progress past the restriction point in G1 depends
on retinoblastoma protein (RB).
RB normally inhibits the cell cycle, but when
phosphorylated by G1-S cyclin-Cdk, RB
becomes inactive and no longer blocks the cell
cycle.
RB + ATP  RB-P + ADP
Active – blocks cell cycle
Inactive – allows cell cycle to go forward