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The Cell Cycle
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Unicellular organisms
– Reproduce by cell division
100 µm
(a) Reproduction. An amoeba,
a single-celled eukaryote, is
dividing into two cells. Each
new cell will be an individual
organism (LM).
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Multicellular organisms use cell division for
– Development from a fertilized cell
– Growth
– Repair
200 µm
(b) Growth and development.
This micrograph shows a
sand dollar embryo shortly
after the fertilized egg divided,
forming two cells (LM).
Figure 12.2 B, C
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
20 µm
(c) Tissue renewal. These dividing
bone marrow cells (arrow) will
give rise to new blood cells (LM).
• Cell division genetically identical daughter
cells
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• DNA molecules packaged into chromosomes
Figure 12.3
50 µm
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Cell cycle consists of
– Mitotic phase
– Interphase
INTERPHASE
G1
S
(DNA synthesis)
G2
Figure 12.5
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Mitotic phase
– Mitosis + cytokinesis
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Mitosis 5 phases
– Prophase
– Prometaphase
G2 OF
INTERPHASE
Centrosomes
Chromatin
(with centriole pairs)
(duplicated)
Figure 12.6
Nucleolus
Nuclear
Plasma
envelope membrane
PROPHASE
Early mitotic
spindle
Aster
Centromere
Chromosome, consisting
of two sister chromatids
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
PROMETAPHASE
Fragments
Kinetochore
of nuclear
envelope
Nonkinetochore
microtubules
Kinetochore
microtubule
– Metaphase
– Anaphase
– Telophase
METAPHASE
ANAPHASE
Metaphase
plate
Figure 12.6
Spindle
Centrosome at Daughter
one spindle pole chromosomes
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
TELOPHASE AND CYTOKINESIS
Cleavage
furrow
Nuclear
envelope
forming
Nucleolus
forming
Cytokinesis
Cleavage furrow
100 µm
Vesicles
forming
cell plate
Contractile ring of
microfilaments
Figure 12.9 A
1 µm
Wall of
patent cell Cell plate New cell wall
Daughter cells
(a) Cleavage of an animal cell (SEM)
Daughter cells
Figure 12.9 B (b) Cell plate formation in a plant cell (SEM)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Bacterial cell division
• 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.
Figure 12.11 4 Two daughter cells result.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Two copies
of origin
Origin
Plasma
Membrane
Bacterial
Chromosome
Origin