1. Cell Division
Chapter 9

2. Evolution of Cell Division
I. Prokaryote Cell Division (Bacteria/Archaea)
A. No nucleus so no mitosis
B. No microtubules or motor proteins to move chromosome.
C. Divide by Prokaryotic fission
1. single circular chromosome binds to cell membrane
2. DNA replication in both directions around circle
3. Cell divides by adding to cell membrane

4. II . Eukaryotic Cell Division
A. DNA contained in nuclear membrane
B. DNA replicated prior to nuclear division
( in interphase)
C. Cell division divided into two parts
1. mitosis = division of nucleus
2. cytokinesis = division of cytoplasm
D. Microtubules and microfilaments needed
E. Motor proteins and ATP required

5. Two Types of Eukaryotic Nuclear Division
I. Mitosis
A. produces clones (daughter cells)
B. unicellular organisms : reproduction
C. Multicellular organisms :
1. asexual reproduction (budding)
2. growth
3. replacement
4. repair

6. II. Meiosis
A. produces haploid cells
1. chromosome number cut in ½
2. non-identical cells
3. gametes
B. only done for sexual reproduction

7. Vocab. Somatic cell – normal diploid body cell Diploid cell –
has 2 copies of each chromosome
Haploid cell –
has 1 copy of each chromosome
Chromosome –
naturally occurring segment of DNA and associated proteins

8. Chromosome forms I. Chromatin - A. DNA wrapped around histones
B. no supercoiling
C. Most DNA available for transcription
D. not visible under microscope
II. Chromatid
A. nucleosomes supercoiled into compact ‘arms’
B. DNA packaged for transport not use
C. condensed chromosomes visible

9. Condensed Chromatids Constriction in center = centromere
= a region of DNA that binds to cohesin proteins that function to hold sister chromatids together
Other cohesins hold sister chromatids together more loosely along their lengths

10. Sister Chromatids Identical Formed by semi-conservative replication
While joined at centromere = 1 chromosome

11. Semi-conservative Replication

12. unduplicated
duplicated
One chromosome
One chromatid
One double helix
One chromosome
(one centromere)
Two chromatids
Two double helixes

13. Genome Genome = all of a cells DNA
All eukaryotes have set # Chromosome in their genome
Humans have 46
Two of each type…
23 different types

14. Mitotic Spindle formation
1) Tubulin subunits in centrosome begin to assemble into
microtubules.
2) microtubules grow toward the center to form spindle fibers
3) short microtubules form a radial array called
an aster
4) centrioles present in animals but not needed

15. Kinetochore Proteins located at centromere
Attachment site for some microtubules of spindle
Polar microtubules overlap with microtubules from opposite pole at center of cell

16. Mitotic Spindle includes: centrosomes, spindle microtubules, & aster
Polar microtubules
centrosome

17. Prophase
Centrosomes begin producing microtubules & moving toward opposite poles
Chromosomes condense into…
chromatids
Nucleoli disappear.
(pro-metaphase)
Nuclear envelope breaks down
Microtubules attach to …
kinetochores
Polar microtubules overlap at equator

18. Metaphase Chromosomes lined up at equator
Pulled by kinetochore microtubules
C line up single file,
One sister chromatid on each side
Centrosomes reach poles

19. Anaphase Cohesin proteins cleaved by Separase enzymes
Separated sister chromatids move toward opposite poles
Kinetochore microtubules shrink as they depolymerize at centrosome
Motor proteins drag chromatids along shrinking microtubules toward poles
Cell elongates as motor proteins push polar microtubules past each other

22. Telophase Begins when chromatids reach poles Microtubules disassemble
Nuclear envelope reforms
Chromosomes
de-condense into
chromatin

23. Cytokinesis Cytokinesis begins before mitosis is complete
Different in plants and animals
Does not always take place

24. Animal cell cytokinesis
Contractile Ring Mechanism
1) a band of microfilaments of the cell cortex contracts
2) indentation forms : cleavage furrow
3) ring contracts until cell membrane is pinched in 2

25. Myosin motor proteins
Move actin filaments
Past each other to tighten
ring

26. Plant Cytokinesis Cell Plate Formation
Vesicles containing cell wall components move
from golgi to equator
Merging vesicle membranes form new cell membrane
Cell wall components assembled in center of merging vesicles form new primary cell wall

27. Primary & Secondary Cell Walls
Primary cell wall : flexible stretchy allows growth
Secondary cell wall: deposited inside primary wall
solid
inflexible
support wall

28. Cell Cycle – Pattern of stages in cell life
Interphase – time spent between cell divisions
(90% of cell cycle)
Mitosis – nuclear division
Cytokinesis – cytoplasmic division

29. Interphase : 3 sub-phases
G1 – gap 1- cell grows ( max size based on..
SA:V ratio)
cell performs its function for the body
cell may never leave G1 (ex nerve cells = G0)
S – synthesis :entire genome is synthesized
by semi-conservative replication
Growth and cell function continue
G2- gap 2 – cell grows & prepares to divide duplicates centrosomes & centrioles (not required: present in animals)

30. Usually, cells will take
interphase hours.
G1 – highly variable
- some cells are in G1 only long enough to grow
- some almost never divide and are said to enter G0
S phase 5 -6 hours
G hours in most cells.
Mitosis, & cytokinesis only takes about 2 hours

31. Cell cycle controlled by Checkpoints
Check points = places where the cell cycle stops
Cell cycle only resumes if certain criteria are met.
Cells signal that the criteria have been met by making checkpoint proteins called cyclins.
Cyclins activate Cyclin Dependent Kinases (CDKs)
CDKs act to signal the cell to move on to the next step in the cell cycle.

32. Cyclin production
When all criteria of a checkpoint are met the specific checkpoint gene for that checkpoint is activated.
The Checkpoint gene contains the instructions for making one specific checkpoint protein (cyclin).
Production of that particular cyclin activates a specific CDK which sets of a chain of reactions that lets the cell cycle pass that checkpoint and continue the cell cycle.
Cyclin breaks down after one use and levels of that type of cyclin drop

34. CDK levels remain constant Cell cycle is controlled by changing levels of Cyclins

35. CDK s : Cyclin Dependent Kinase function
Kinase = group of enzymes that phosphorylate proteins (activate them)
CDKs are a type of Kinase that only functions when bound to cyclin.
Different versions of cyclin activate different CDKs.
Each activated CDK phosphorylates a different protein.
Activating (phosphorylating) that proteins sets off a transduction cascade that transduces the signal to proceed to the next checkpoint

36. Animal cells stay in G1 or G0 unless signaled by growth factors

37. Check points – regulated by CDKs
1) G1 checkpoint – cycle initiation
a)controlled by cell size
b) growth factors
c) environment
2) G2 checkpoint – transition to M
a) DNA replication complete
b) DNA damage/mutations
3) M-spindle checkpoint
a) spindle attachment

38. Growth Factors …
1. are signal molecules
2. released by cells to signal nearby cells to divide
3. diffuse through intracellular fluids
4. bind to membrane receptors on target cell
5. transduction of signal causes cyclin production
6. cyclins activate CDK
7. CDK phosphorylates first protein of cascade that moves cell past G1 checkpoint
8. are an example of cell-to- cell communication

39. Example growth factor = PDGF Platelet-derived Growth Factor
PDGF released by platelets cause
Fibroblast(wound repair) cells to divide
1) PDGF binds to receptor on Fibroblast
2) signal transduction pathway initiated
3) cell passes G1 checkpoint and starts to divide

40. Animal cells stay in G1 or G0 unless signaled by growth factors

41. Cyclin-CKD example : MPF
M-phase Promoting Factor =
CDK-cyclin complex
STEPS
checkpoint gene for MPF cyclin is activated
MPF cyclin levels build up & build MPF levels
High enough concentration of MPF allows
Cell to move from G2 into M phase
MPF concentration reduced in Anaphase by breakdown of
cyclin causing MPF to revert to
inactive CDK

42. CKI = Cyclin Dependent Kinase Inhibitors
Inhibitors stop things
CKIs stop the CDK enzymes from working
Example:
CKI p21 stops CDK2 from working…thus
Stopping the transition from G1 – S phase
The CKI inhibitor molecule p21 is only active when tumor suppressor gene p53 is transcribed (copied) *** know p53 ***

43. Normal Cell Division Cell Division limited by:
1) Density-dependent Inhibition
cells that are crowded stop dividing
2) Anchorage dependency –
cell must be anchored to extra-cellular matrix of a tissue to divide.

44. Cell Division in Cancer Cells
Cancer Cells NOT inhibited by density or anchorage
CC do NOT stop dividing when out of Growth Factor
CC do not follow signals of check point genes
CC do not self-destruct by apoptosis

45. Origin of Cancer Cells 1 cell undergoes transformation (damage to DNA)
Transformed cell avoids immune system
avoids apoptosis
ignores regular cell cycle signals
uncontrolled cell division
Benign tumor : cells stay anchored
Malignant tumor cells spread = cancer
Metastasis = spread of cancer cells

46. Uncontrolled cell division
Results from the failure of more than one checkpoint gene
Which causes non-functional checkpoint proteins
Causes tumor development
May cause cancer

47. Cancer Cell Changes Mutation of Check Point Genes
Change in chromosome number/structure
Abnormal/irregular cell membrane
lacks attachment proteins
damaged signal/receptor proteins
Secrete signal molecules that encourage blood vessel growth

48. Cancer Treatment Radiation for localized tumor
Chemotherapy – poisons most damaging to dividing cells