1. The Mitotic Spindle: A Closer Look
The mitotic spindle is an apparatus of microtubules that controls chromosome movement during mitosis
During prophase, assembly of spindle microtubules begins in the centrosome, the microtubule organizing center
The centrosome replicates, forming two centrosomes that migrate to opposite ends of the cell, as spindle microtubules grow out from them
For the Cell Biology Video Spindle Formation During Mitosis, go to Animation and Video Files.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

2. An aster (a radial array of short microtubules) extends from each centrosome
The spindle includes the centrosomes, the spindle microtubules, and the asters
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

3. During prometaphase, some spindle microtubules attach to the kinetochores of chromosomes and begin to move the chromosomes
At metaphase, the chromosomes are all lined up at the metaphase plate, the midway point between the spindle’s two poles
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

4. Fig. 12-7
Aster
Centrosome
Sister
chromatids
Microtubules
Chromosomes
Metaphase
plate
Kineto-
chores
Centrosome
1 µm
Figure 12.7 The mitotic spindle at metaphase
Overlapping
nonkinetochore
microtubules
Kinetochore
microtubules
0.5 µm

5. The microtubules shorten by depolymerizing at their kinetochore ends
In anaphase, sister chromatids separate and move along the kinetochore microtubules toward opposite ends of the cell
The microtubules shorten by depolymerizing at their kinetochore ends
For the Cell Biology Video Microtubules in Anaphase, go to Animation and Video Files.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

6. EXPERIMENT RESULTS CONCLUSION Kinetochore Spindle pole Mark Chromosome
Fig. 12-8
EXPERIMENT
Kinetochore
Spindle
pole
Mark
RESULTS
Figure 12.8 At which end do kinetochore microtubules shorten during anaphase?
CONCLUSION
Chromosome
movement
Kinetochore
Motor
protein
Tubulin
subunits
Microtubule
Chromosome

7. EXPERIMENT Kinetochore Spindle pole Mark RESULTS Fig. 12-8a
Figure 12.8 At which end do kinetochore microtubules shorten during anaphase?
RESULTS

8. Chromosome movement Kinetochore Tubulin Motor Subunits Microtubule
Fig. 12-8b
CONCLUSION
Chromosome
movement
Kinetochore
Tubulin
Subunits
Motor
protein
Microtubule
Figure 12.8 At which end do kinetochore microtubules shorten during anaphase?
Chromosome

9. Nonkinetochore microtubules from opposite poles overlap and push against each other, elongating the cell
In telophase, genetically identical daughter nuclei form at opposite ends of the cell
For the Cell Biology Video Microtubules in Cell Division, go to Animation and Video Files.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

10. Cytokinesis: A Closer Look
In animal cells, cytokinesis occurs by a process known as cleavage, forming a cleavage furrow
In plant cells, a cell plate forms during cytokinesis
Animation: Cytokinesis
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

11. Video: Sea Urchin (Time Lapse)
Video: Animal Mitosis
Video: Sea Urchin (Time Lapse)
For the Cell Biology Video Nuclear Envelope Formation, go to Animation and Video Files.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

12. Figure 12.9 Cytokinesis in animal and plant cells
Vesicles
forming
cell plate
Wall of
parent cell
1 µm
100 µm
Cleavage furrow
Cell plate
New cell wall
Figure 12.9 Cytokinesis in animal and plant cells
Contractile ring of
microfilaments
Daughter cells
Daughter cells
(a) Cleavage of an animal cell (SEM)
(b) Cell plate formation in a plant cell (TEM)

13. (a) Cleavage of an animal cell (SEM)
Fig. 12-9a
100 µm
Cleavage furrow
Figure 12.9a Cytokinesis in animal and plant cells
Contractile ring of
microfilaments
Daughter cells
(a) Cleavage of an animal cell (SEM)

14. (b) Cell plate formation in a plant cell (TEM)
Fig. 12-9b
Vesicles
forming
cell plate
Wall of
parent cell
1 µm
Cell plate
New cell wall
Figure 12.9b Cytokinesis in animal and plant cells
Daughter cells
(b) Cell plate formation in a plant cell (TEM)

15. 10 µm Fig. 12-10 Nucleus Chromatin condensing Nucleolus Chromosomes
Cell plate
Figure Mitosis in a plant cell 1
Prophase 2
Prometaphase 3
Metaphase 4
Anaphase 5
Telophase

16. Nucleus 1 Prophase Chromatin condensing Nucleolus Fig. 12-10a
Figure Mitosis in a plant cell 1
Prophase

17. Chromosomes 2 Prometaphase Fig. 12-10b
Figure Mitosis in a plant cell 2
Prometaphase

18. Fig c
Figure Mitosis in a plant cell 3
Metaphase

19. Fig d
Figure Mitosis in a plant cell 4
Anaphase

20. 10 µm Cell plate 5 Telophase Fig. 12-10e
Figure Mitosis in a plant cell 5
Telophase

21. Binary Fission
Prokaryotes (bacteria and archaea) reproduce by a type of cell division called binary fission
In binary fission, the chromosome replicates (beginning at the origin of replication), and the two daughter chromosomes actively move apart
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

22. Cell wall Origin of replication Plasma membrane E. coli cell Bacterial
Fig
Cell wall
Origin of
replication
Plasma
membrane
E. coli cell
Bacterial
chromosome
Two copies
of origin
Figure Bacterial cell division by binary fission

23. Cell wall Origin of replication Plasma membrane E. coli cell Bacterial
Fig
Cell wall
Origin of
replication
Plasma
membrane
E. coli cell
Bacterial
chromosome
Two copies
of origin
Origin
Origin
Figure Bacterial cell division by binary fission

24. Cell wall Origin of replication Plasma membrane E. coli cell Bacterial
Fig
Cell wall
Origin of
replication
Plasma
membrane
E. coli cell
Bacterial
chromosome
Two copies
of origin
Origin
Origin
Figure Bacterial cell division by binary fission

25. Cell wall Origin of replication Plasma membrane E. coli cell Bacterial
Fig
Cell wall
Origin of
replication
Plasma
membrane
E. coli cell
Bacterial
chromosome
Two copies
of origin
Origin
Origin
Figure Bacterial cell division by binary fission