1. Mitosis and Cytokinesis
Ch 9 The Cell Cycle
Mitosis and Cytokinesis

2. Cell Division
In unicellular organisms, division of one cell reproduces the entire organism
Multicellular organisms depend on cell division for:
Development from a fertilized cell
Growth
Repair
Cell division is an integral part of the cell cycle, the life of a cell from formation to its own division
Mitosis
Meiosis
Binary Fission

3. Genetic Material Chromosome – coiled DNA – Cell Division
Chromatin – uncoiled DNA
DNA that is being transcribed – converted to mRNA
Chromatid – ½ duplicated chromosome
Sister chromatids – same DNA (copies)
Centromere – holds chromatids together

4. Mitosis vs. Meiosis

5. Mitosis vs. Meiosis Mitosis Meiosis 2 identical daughter cells
Somatic cells – body cells
Diploid (2n) – 46 chromosomes in humans
No variation
Copies DNA once – S phase
Meiosis
4 non-identical cells
Gametes – sex cells
Sperm and egg
Haploid (n) – 23 chromosomes in humans
Variation
Crossing over
Independent assortment
Random fusion of gametes
Copies DNA once – S phase

6. The Cell Cycle Interphase Mitotic Phase: G1: first gap S: growth
growth and normal metabolism
S: growth
metabolism AND chromosome replication
G2: second gap
growth and prep for mitosis
Mitotic Phase:
Mitosis: nuclear division
Cytokinesis: cytoplasmic division
Plant: Cell plate (vesicles from Golgi form new cell wall)
Animal: Cleavage furrow (actin and myosin filaments)12_09Cytokinesis_A.swf

7. Mitosis pgs. 178-179 Prophase Prometaphase Metaphase (longest)
Nucleoli dissappear, mitotic spindle formed, sister chromatids
Prometaphase
Nuclear envel. Fragments, microtubules invade nuclear area, kinetichore microtubules move chromosomes
Metaphase (longest)
Centrosomes at opposite sides, chromosomes on metaphase Anaphase (shortest) 12_06Mitosis.mpg
Cohesion proteins (holding sister chromatids) cleaved, kinetichore microtubules shorten and pull chromosomes toward opposite ends, cell elongates
Telophase
Daughter nuclei form, nucleoli reappear, chromosomes become less condensed

8. Review the structure and function of the cytoskeleton on pgs. 84-86.
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
Review the structure and function of the cytoskeleton on pgs
0.5 µm

9. Concept Check
What role do motor proteins play in mitosis (pg 180)? What would happen to a cell if a microtubule could not interact properly with tubulin during anaphase?

10. Binary Fission Prokaryotes and Archea
Circular DNA of cell begins to elongate
2 Origins of replication
One origin moves to opposite end of cell
Cell elongates
When replication is complete, the cell divides
Yields 2 identical daughter cells

11. Internal Regulation of the cell cycle
Control system
G2 checkpoint
M checkpoint
G1 checkpoint G1 S G2 M

12. Cell Cycle Regulation & Checkpoints
Stop and go signals
G1 “Restriction point”
Seems to be most important, if a cell passes it, cell will go through all phases
If a cell doesn’t pass G1, it will go to G0 a non-dividing stage.
G2 Checkpoint
Cdk’s initiates Mitosis
M Checkpoint
Chromosomes attached to metaphase plate = anaphase happens
G0 Phase
Non dividing, most cells are in this stage

13. (b) Cell does not receive a go-ahead signal
Fig G0
G1 checkpoint
Figure The G1 checkpoint G1 G1
Cell receives a go-ahead
signal
(b) Cell does not receive a
go-ahead signal

14. Cyclin dependent kinases – Cdks Not in text
Cyclin + Cdks = passage through the checkpoint
A kinase that is activated by a cyclin, the Cdk will then phosphorylate an enzyme to cause mitosis to proceed.
MPF – cyclin Cdk that promotes mitosis
If present mitosis happens
If absent mitosis does not happen

15. Protein kinase activity (– )
Fig
RESULTS
Notice how cell division follows protein kinase activity 5 30 4 20 3
% of dividing cells (– )
Protein kinase activity (– ) 2 10 1
Figure How does the activity of a protein kinase essential for mitosis vary during the cell cycle?
100
200
300
400
500
Time (min)

16. External Signals that control Cell Cycle
Density Dependent
Cultured cells normally divide until they form a single layer on the inner surface of the culture container.
If a gap is created, cell will fill the gap.
Growth Factors
proteins released by one group of cells that stimulate other cells to divide. At least 50 different growth factors can trigger specific cells to divide.
Anchorage Dependent
To divide, they must be anchored to a substratum, typically the extracellular matrix (ECM)of a tissue.
Control appears to be mediated by pathways involving plasma membrane proteins and elements of the cytoskeleton linked to them.

17. Cancer Cells Do not respond to signals of the cell cycle, “trick” the immune system, and cause growth of blood vessels to cancer cells for nutrition.
Transformation: a normal cells converts to a cancer cell
Benign: abnormal cells remain in one location (rarely cause disease)
Malignant: abnormal cells impair functions of one or more organs
Metastasis: cancer cells spread to surrounding tissue or throughout body using circulatory system
Abnormal Chromosome #