1. AP Biology
Mitosis

2. Mitosis vs. Meiosis
Mitosis: Cell Division that produces two diploid cells that are identical to each other and to the parent cell.
This produces body cells (somatic cells) so the organism can grow or replace dead/damaged cells.
Meiosis: Cell division that produces four haploid cells that are not identical genetically.
This produces sex cells (gametes) that are used in sexual reproduction.

3. “C” Words:
Chromatin-Strands of DNA in a cell that is not dividing—unwound and indistinct.
Chromosomes-Strands of DNA in a cell that is dividing—wound up and distinct.
Chromatin is unwound and indistinct in the nucleus of the cell.

4. More “C” Words:
Chromatids—one of 2 identical strands of DNA in a chromosome (called sister chromatids)
Centromere—the structure that holds together the 2 sister chromatids.
Histones-protein “beads” that keep the strand of DNA from tangling up.

5. More “C” Words
Centrosome/Centriole-Structure found in animal cells that anchors the spindle fibers; made of bundles of microtubules.
Cytokinesis—the division of the cytoplasm following mitosis (the dividing of the nucleus)

6. Chromosome Structure
When cells begin to divide, the first thing that happens is that the chromatin in the nucleus begins to wind up, separating the strands from each other.
This forms individual chromosomes, each with two identical chromatids.
Each chromosome consists of 2 identical strands of DNA (called sister chromatids) held together with a centromere.

7. Cell Cycle

8. Interphase DNA is in the form of chromatin here: Interphase
A cell in Interphase is not actively dividing. It is working very hard, however—growth, replicating DNA and preparing to divide.

9. Prophase
Prophase
Centrioles migrate to the poles. Nuclear Membrane disappears.
Chromatin winds up to form chromosomes.
Spindle forms.

10. Metaphase Metaphase Metaphase
Chromosomes move to the equator of the cell.

11. Anaphase Chromosomes split in half at centromere.
Each chromatid moves to opposite poles.

12. Chromosome Structure At Anaphase
Chromosomes prior to Anaphase
Centromere splits and chromatids go to opposite poles of cell

13. Kinetochores
Kinetochores are structures that are part of the spindle fiber system.
They attach to chromosomes at the centromere.
During Anaphase, they shorten and move toward the poles, pulling apart the chromatids.

14. Telophase Telophase Chromosomes unwind to form chromatin again.
New nuclear membranes form.
Spindle disappears

15. Cytokinesis
Cytokinesis in a Plant Cell: A cell plate forms between the 2 new nuclei—eventually dividing the cell into 2 cells. The cell plate becomes the new cell wall.
Cytokinesis in an Animal Cell: A cleavage furrow forms, eventually pinching in the cell membrane to form 2 cells.

16. Cytokinesis in Animal Cells (on left) and Plant Cells (on right)

17. Regulation of Mitosis
How often cells divide depends on many factors. For example, the age of the organism and type of cell greatly affects how often it divides.
Example: skin cells divide frequently; mature nerve cells and muscles cells never divide.
What determines when a cell divides? Signals!

18. Signal Transduction
Transduction = the relaying of a message from one molecule to another
When a cell has a receptor for a particular molecule on its surface, it will send a “signal” into the cell when that molecule arrives.
This “signal” is usually relayed
to other molecules and
activates a certain response
inside the cell.

19. The Cell Cycle Control System
The sequential events of the cell cycle are directed by a distinct cell cycle control system, which is similar to a clock
The cell cycle control system is regulated by both internal and external controls
The clock has specific checkpoints where the cell cycle stops until a go-ahead signal is received
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

20. G1 checkpoint Control system S G1 G2 M M checkpoint G2 checkpoint
Fig
G1 checkpoint
Control
system S G1 G2 M
Figure Mechanical analogy for the cell cycle control system
M checkpoint
G2 checkpoint

21. 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
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

22. (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

23. 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)
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
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

24. (a) Fluctuation of MPF activity and cyclin concentration during
Fig a M G1 S G2 M G1 S G2 M G1
MPF activity
Cyclin
concentration
Figure Molecular control of the cell cycle at the G2 checkpoint
Time
(a) Fluctuation of MPF activity and cyclin concentration during
the cell cycle

25. (b) Molecular mechanisms that help regulate the cell cycle
Fig b G1 S
Cdk
Cyclin accumulation M
Degraded
cyclin G2 G2
checkpoint
Cdk
Figure Molecular control of the cell cycle at the G2 checkpoint
Cyclin is
degraded
Cyclin
MPF
(b) Molecular mechanisms that help regulate the cell cycle

26. Stop and Go Signs: Internal and External Signals at the Checkpoints
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
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

27. 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

28. Another example of external signals is density-dependent inhibition, in which crowded cells stop dividing
Most animal cells also exhibit anchorage dependence, in which they must be attached to a substratum in order to divide
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

29. 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
Cancer cells exhibit neither anchorage dependence nor density-dependent inhibition.

30. Loss of Cell Cycle Controls in Cancer Cells
Cancer cells do not respond normally to the body’s control mechanisms
Cancer cells may not need growth factors to grow and divide:
They may make their own growth factor
They may convey a growth factor’s signal without the presence of the growth factor
They may have an abnormal cell cycle control system
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

31. A normal cell is converted to a cancerous cell by a process called transformation
Cancer cells form tumors, masses of abnormal cells within otherwise normal tissue
If abnormal cells remain at the original site, the lump is called a benign tumor
Malignant tumors invade surrounding tissues and can metastasize, exporting cancer cells to other parts of the body, where they may form secondary tumors
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

32. Lymph vessel Tumor Blood vessel Cancer cell Glandular tissue
Fig
Lymph
vessel
Tumor
Blood
vessel
Cancer
cell
Glandular
tissue
Metastatic
tumor 1
A tumor grows
from a single
cancer cell. 2
Cancer cells
invade neigh-
boring tissue. 3
Cancer cells spread
to other parts of
the body. 4
Cancer cells may
survive and
establish a new
tumor in another
part of the body.
Figure The growth and metastasis of a malignant breast tumor

33. Mitosis Animations http://www.cellsalive.com/mitosis.htm