Chapter 9
The
Cell
Cycle
Cell Division: Key Terms






Genome: cell’s genetic
information
Somatic (body cells) cells
Gametes (germ cells):
sperm and egg cells
Chromosomes: DNA
molecules
Diploid (2n): 2 sets of
chromosomes
Haploid (1n): 1 set of
chromosomes
Cell Division: Key Terms






Chromatin: DNA-protein
complex
Chromatids: replicated
strands of a chromosome
Centromere: narrowing
“waist” of sister
chromatids
Mitosis: nuclear division
Cytokinesis: cytoplasm
division
Meiosis: gamete cell
division
Purpose of cell division
 Multicellular
division for
organisms depend on cell
• Development from a fertilized cell
• Growth
200 µm
• Repair
20 µm
(b) Growth and development.
(c) Tissue renewal. These dividing
This micrograph shows a
bone marrow cells (arrow) will
sand dollar embryo shortly
give rise to new blood cells (LM).
after the fertilized egg divided,
forming two cells (LM).
The Cell Cycle
Interphase (90% of
cycle)
 G1 phase~ growth
 S phase~ synthesis
of DNA
 G2 phase~
preparation for
cell division

The Cell Cycle
Mitotic phase
 Mitosis~ nuclear
division
 Cytokinesis~
cytoplasm
division

Mitosis
Prophase
 Prometaphase
 Metaphase
 Anaphase
 Telophase

Mitosis Animation
Spindle microtubules
Aster
Sister
chromatids
Centrosome
Metaphase
Plate
Kinetochores
Overlapping
nonkinetochore
microtubules
Kinetochores
microtubules
Microtubules
Chromosomes
Centrosome
1 µm
Prophase
Chromosomes
visible
 Nucleoli disappear
 Sister chromatids
 Mitotic spindle
forms
 Centrosomes move

Prometaphase
Nuclear membrane
fragments
 Spindle interaction
with chromosomes
 Kinetochore
develops

QuickTime™ and a
Cinepak decompressor
are needed to see this picture.
Metaphase
Centrosomes at
opposite poles
 Centromeres are
aligned
 Kinetochores of
sister chromatids
attached to
microtubules
(spindle)

QuickTime™ and a
Cinepak decompressor
are needed to see this picture.
Anaphase
Paired centromeres
separate; sister
chromatids
liberated
 Chromosomes move
to opposite poles
 Each pole now has a
complete set of
chromosomes

QuickTime™ and a
Cinepak decompressor
are needed to see this picture.
Telophase
Daughter nuclei
form
 Nuclear envelopes
reappear
 Chromatin becomes
less coiled
 Two new nuclei
complete mitosis

QuickTime™ and a
Cinepak decompressor
are needed to see this picture.
Cytokinesis
 Cytoplasmic
division
 Animals~
cleavage furrow
Cleavage furrow
Contractile ring of
microfilaments
100 µm
Daughter cells
(a) Cleavage of an animal cell (SEM)
Cytokinesis
 In
plant cells,
during cytokinesis
• A cell plate forms
Vesicles
forming
cell plate
Wall of
parent cell Cell plate New cell wall
Daughter cells
(b) Cell plate formation in a plant cell (SEM)
Binary Fission
 Prokaryotes
(bacteria)
• Reproduce by a type of cell division
called binary fission
• The bacterial chromosome replicates
• The two daughter chromosomes actively
move apart
Binary Fission
Origin of
replication
Cell wall
E. coli cell
1 Chromosome replication begins.
Soon thereafter, one copy of the
origin moves rapidly toward the
other end of the cell.
2 Replication continues. One copy of
the origin is now at each end of
the cell.
3 Replication finishes. The plasma
membrane grows inward, and
new cell wall is deposited.
4 Two daughter cells result.
Two copies
of origin
Origin
Plasma
Membrane
Bacterial
Chromosome
Origin
The Evolution of Mitosis
 Since
prokaryotes preceded
eukaryotes by billions of years
• It is likely that mitosis evolved from
bacterial cell division
 Certain
protists
• Exhibit types of cell division that seem
intermediate between binary fission and
mitosis carried out by most eukaryotic
cells
Cell Cycle Regulation
Growth factors
 Density-dependent
inhibition
 Anchorage
dependence

The Cell Cycle Control
System
 The
sequential events of the
cell cycle
G checkpoint
1
Control
system
G1
M
G2
M checkpoint
G2 checkpoint
S
The clock has specific checkpoints
Where the cell cycle stops until a go-ahead
signal is received
G0
G1 checkpoint
G1
(a) If a cell receives a go-ahead signal at
the G1 checkpoint, the cell continues
on in the cell cycle.
G1
(b) If a cell does not receive a go-ahead
signal at the G1checkpoint, the cell
exits the cell cycle and goes into G0, a
nondividing state.
The Cell Cycle Clock: Cyclins and
Cyclin-Dependent Kinases
 Two
types of regulatory proteins are
involved in cell cycle control
 Cyclins and cyclin-dependent kinases
(Cdks)
Loss of Cell Cycle Controls in
Cancer Cells
 Cancer
cells
• Do not respond normally to the body’s
control mechanisms
• Form tumors
Cancer
Transformation
 Tumor: benign or malignant
 Metastasis
