1. Cell Cycle and Mitosis 8.1 to 8.11
In eukaryotes, heritable information is passed to the next generation via processes that include the cell cycle and mitosis or meiosis plus fertilization
Cell Cycle and Mitosis 8.1 to 8.11

2. Genetic information is stored and transmitted through DNA
All the DNA in a cell constitutes the cell’s genome
A genome can consist of a single DNA molecule (common in prokaryotic cells) or a number of DNA molecules (common in eukaryotic cells)
DNA molecules in a cell are packaged into chromosomes
Genetic information is stored and transmitted through DNA

3. Fig. 12-3
Figure 12.3 Eukaryotic chromosomes
20 µm

4. Genetic Information is stored and transmitted through DNA
Every eukaryotic species has a characteristic number of chromosomes in each cell nucleus
Somatic cells (nonreproductive cells) have two sets of chromosomes - DIPLOID
Gametes (reproductive cells: sperm and eggs) have half as many chromosomes as somatic cells - HAPLOID
Eukaryotic chromosomes consist of chromatin, a complex of DNA and protein that condenses during cell division
Genetic Information is stored and transmitted through DNA

5. 0.5 µm Chromosomes DNA molecules Chromo- some arm Chromosome
Fig. 12-4
0.5 µm
Chromosomes
DNA molecules
Chromo-
some arm
Chromosome
duplication
(including DNA
synthesis)
Centromere
Sister
chromatids
Figure 12.4 Chromosome duplication and distribution during cell division
Separation of
sister chromatids
Centromere
Sister chromatids

6. The cell cycle is a complex set of stages that is highly regulated with checkpoints, which determine the ultimate fate of the cell

7. Interphase Majority of the cell cycle
Time when a cell’s metabolic activity is very high and the cell performs various functions
3 stages
G1 – cell growth
S – DNA replication (Synthesis of DNA)
G2 – prepare for mitosis
Interphase

8. M Phase (mitotic phase)
About 10% of the cell cycle
2 stages
Mitosis – nuclear division
Cytokinesis – cytoplasm division
Results in two genetically identical cells
M Phase (mitotic phase)

9. The cell cycle is directed by internal controls or checkpoints.

10. Cell Cycle Checkpoints
For many cells, the G1 checkpoint seems to be the most important one
If a cell receives a go-ahead signal at the G1 checkpoint, it will usually complete the S, G2, and M phases and divide
If the cell does not receive the go-ahead signal, it will exit the cycle, switching into a nondividing state called the G0 phase
Cell Cycle Checkpoints

11. Cell Cycle Checkpoints
Two types of regulatory proteins are involved in cell cycle control: cyclins and cyclin- dependent kinases (Cdks)
The activity of cyclins and Cdks fluctuates during the cell cycle
MPF (maturation-promoting factor) is a cyclin-Cdk complex that triggers a cell’s passage past the G2 checkpoint into the M phase
Cell Cycle Checkpoints

12. M G1 S G2 M G1 S G2 M G1 Fig. 12-17 MPF activity Cyclin concentration
Time
(a) Fluctuation of MPF activity and cyclin concentration during
the cell cycle G1 S
Cdk
Figure Molecular control of the cell cycle at the G2 checkpoint
Cyclin accumulation M
Degraded
cyclin G2 G2
Cdk
Cyclin is
degraded
checkpoint
Cyclin
MPF
(b) Molecular mechanisms that help regulate the cell cycle

13. An example of an internal signal is that kinetochores not attached to spindle microtubules send a molecular signal that delays anaphase
Some external signals are growth factors, proteins released by certain cells that stimulate other cells to divide
For example, platelet-derived growth factor (PDGF) stimulates the division of human fibroblast cells in culture
Internal and External signals provide stop-and-go signs at the checkpoints

14. Scalpels Petri plate Without PDGF cells fail to divide With PDGF
Fig
Scalpels
Petri
plate
Without PDGF
cells fail to divide
Figure The effect of a growth factor on cell division
With PDGF
cells prolifer-
ate
Cultured fibroblasts
10 µm

15. Density-dependent inhibition
Fig
Anchorage dependence
Density-dependent inhibition
Density-dependent inhibition
Figure Density-dependent inhibition and anchorage dependence of cell division
25 µm
25 µm
(a) Normal mammalian cells
(b) Cancer cells

16. Mitosis is conventionally divided into five phases:
Prophase
Prometaphase
Metaphase
Anaphase
Telophase
Cytokinesis is well underway by late telophase
Mitosis passes a complete genome from the parent cell to the daughter cell

17. G2 of Interphase Prophase Prometaphase Centrosomes (with centriole
Fig. 12-6b
G2 of Interphase
Prophase
Prometaphase
Centrosomes
(with centriole
pairs)
Chromatin
(duplicated)
Early mitotic
spindle
Aster
Centromere
Fragments
of nuclear
envelope
Nonkinetochore
microtubules
Figure 12.6 The mitotic division of an animal cell
Nucleolus
Nuclear
envelope
Plasma
membrane
Chromosome, consisting
of two sister chromatids
Kinetochore
Kinetochore
microtubule

18. 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

19. Telophase and Cytokinesis
Fig. 12-6d
Metaphase
Anaphase
Telophase and Cytokinesis
Metaphase
plate
Cleavage
furrow
Nucleolus
forming
Figure 12.6 The mitotic division of an animal cell
Daughter
chromosomes
Nuclear
envelope
forming
Spindle
Centrosome at
one spindle pole

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

21. 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)

22. Summary of Mitosis What must occur before mitosis?
DNA replication
Pass G2 checkpoint
What is “checked” at the ‘M’ checkpoint?
Chromosome attachment to microtubule
What follows mitosis?
Cytokinesis
What are the products of the mitosis?
2 genetically identical cells
Why do we need mitosis?
Growth, repair, asexual reproduction
Summary of Mitosis