1. Cell Growth, Replication and Division
The Cell Cycle
Chapter 12
Cell Growth, Replication and Division

2. The Cell Cycle Every cells arises from a pre-existing cell
Plant cells arise from plants,
Animal cells from animal cells
All cells in a multicellular organism are genetically identical
We will come back to mutation/Evolutionary change

3. The Cell Cycle Replication is only one part of the cell cycle
Growth is necessary to prepare for division
Replication is the act of making two cells from one
Cellular replication requires a series of events in the cell to copy and equally disperse DNA: Mitosis

4. Cell Replication DNA stores genetic information
Genetic information must be duplicated to form new cell
And dispersed into new cells
Genetic information is important to make and operate cells
DNA must be condensed after duplication for dispersal
Forming chromosomes
The Cell Cycle is a series of events to copy and equally disperse DNA in to daughter cells

5. DNA Replication Original strand of DNA unwound
The two complementary strand separate
Each is used to create a new complementary strand
DNA has been duplicated

6. What is a Chromosome?
DNA is “Supercoiled” to condense in an organized manner, creating chromosomes

7. What is a Chromosome? Condensed DNA is able to move more easily
Structural stability

8. During Cell Division Every chromosome is copied
The copies are placed into separate cells

9. Genetic Division DNA is duplicated
the identical copies of chromosomes remain connected at the centromere
This prepares the two copies (sister chromatids) for cellular division

10. The Cell Cycle

11. Control System Checkpoints G1 – Gap 1 G2 – Gap 2 M – Mitosis
G1 – during growth, before DNA dulpication
G2 – Before mitosis
M – before mitosis is complete (to ensure proper division)

12. Mitosis
During Mitosis the cell goes through several key stages to properly divide up the genetic material, organelles and cytoplasm to create two living cells

13. Mitotic Stages The 5 Stages of Mitosis are: Prophase Prometaphase
Anaphase
Telophase
Cytokenesis

14. The end of G2 DNA has been duplicated
Formed chromatin
Organelles have been duplicated (including centrioles)
The Cell has undergone enough cytoplasmic growth
The Cell is ready to divide…

15. 2. Prophase The Chromatin begins to coil into Chromosomes
Sister chromatids attached at the centromere
The Centrioles move apart forming a microtubules lattice called the Mitotic Spindle
The Nuclear membrane breaks apart

16. 3. Prometaphase The nuclear envelope continues to break apart
The Centrioles finish their migration to opposite poles of cell
The spindle extends microtubules into the nuclear area

17. 4. Metaphase
The chromosomes line up along an imaginary mid-line called the metaphase plate
Every pair of chromosomes are pulled in line
Microtubules from each centriole catch every pair of chromatids at Kinetochore

18. 4. Anaphase
The proteins (cohesin) binding sister chromatids are broken down
The two chromatids are pulled to opposite centromeres
Microtubules not connected to a chromosome push
cause the cell to elongate
by cohesinase

19. 4. Telophase
The nuclear envelopes reforms around two separate sets of DNA
The mitotic spindle breaks down
A microfilament ring being to form between the two nuclei

20. Cytokenesis and Cleavage
Microfilaments Contractile Ring
Constricts creating a Cleavage Furrow
Will eventually separate the two cells
Cytokinesis – the division of cytoplasm

21. The Metaphase Plate
The aster microtubules are in contact with the cell membrane to give them stability when seperating the choromosomes
An imaginary Plane on which the chromosomes line up before being separated

22. Anaphase How are the chromosomes pulled apart?
Motor proteins form connection between microtubule & kinetochore
During Anaphase the motor proteins pull chromosome along the microtubule
towards the centromere

23. Microtubule
Movement
Motor Protein
My favorite anology
Chromosome

24. Cytokinesis in Animals
The contractile ring pinches off the cell membrane between the two daughter cells
Cleavage furrow forms along the metaphase plate
Like pinching a balloon

25. Cytokenesis in Plants Cell Plate forms between the nuclei
Cellulose produced from golgi
Cell plate extends to the parental cell wall
And cell membrane reforms along the cell plate

26. Mitosis in Plants Mitotic stages the same Plants lack centromeres
so microtubles connect to membrane/cell wall at opposite poles
Formation of the cell plate during cytokenesis

27. Growth in Plants

28. Binary Fission
Asexual reproduction in Prokaryotes

29. Evolution of Mitosis
Eukaryotes have significantly larger genomes than prokaryotes
23 – 76x larger
Must find a way to correctly copy and divide genome

30. Evolution of Mitosis Evolution is a step-wise series of changes.
Trace changes through Evolutionary history
Evolution of Mitosis

31. Dinoflagellates Unicellular eukaryotes
“Plankton”, A dietary staple of many larger organisms.
Pre-historic organism that have remained relatively unchanged for millions of years
Living Fossil

32. Evolution of Mitosis
Dinoflagellates Nuclei remains intact during division
Chromosomes attached to nuclear envelope
Microtubules pass through nucleus to divide cells

33. Evolution of Mitosis In Diatoms and Yeast the nucleus remains intact
Mitotic Spindle forms within the nuclear envelope

34. Evolution

35. Molecular Control System
Checkpoints exist to prevent cell from proceeding if not ready
3 major checkpoints in eukaryotic cell cycle
Signals in the cytoplasm signal the movement between stages of the cell cycle

36. Molecular Control System
If the cell meets the requirements of a checkpoint it is allowed to pass
Signal transduction pathways are use to determine if the cell meets requirements

37. Molecular Control System
If a cell does not meet requirements it remains at that stage until ready
Cell may also enters G0 phase
A non-dividing state
It may re-enter the cell cycle later

38. Cyclins Protein kinase Cdc2 Binds to Cyclin protein
Cyclin-Dependent Kinases (Cdks)

39. Cyclins As cyclin concentration increases Cdk activity increases
Signaling the cell to enter Mitosis
Activated Cdc2 being a signalling pathway that overcomes the final checkpoint and beings the signalling cascades of mitosis

40. Growth Factors Protein signals that instruct other cells to divide
Signaling pathways
PDGF is a growth factor

41. Density dependent inhibition
When cell density gets high enough cells stop dividing

42. Cancerous Cells
Loss of density dependence and contact inhibition

43. Cancerous Cells
Through a series of mutations cells loose the normal cell cycle controls
Continue to divide

44. Cancerous Cells
Cancerous cells can leave the mass (tumor) and can enter the lymph or blood systems
spreading throughout the body.

45. Cell Replacement
It is important for some cells to be replaced over time
Cells become damaged, loss of function
What types of cells are rarely replaced?
Or never replaced?
What types of cells are frequently replaced?

46. Rates of replacement Skin cells – 35 days Red blood cells – 120 days
Skeletal & Fat cells – 10 years
Heart Cells (Cardiomyocytes) – about 50% over a lifetime
Cerebral Neurons - Never

47. Liver & Skin cells Constantly replicating, replace cells
Liver – removes toxins from the blood
Taxing on the cells, so must constantly replenish
This is why doctors can take part of your liver for a transplant (but not part of a kidney)
Skin – exposed to the environment
Including your digestive system lining

48. Scar tissue

49. Alzheimer's Neurons stop replicating Paralysis – severed neurons
Enter G0 and remain there indefinitely
Researchers trying to figure out why these cells stop replicating
Reverse the process so that brain cells can re-generate
Paralysis – severed neurons
Can Re-attached limbs regain function?
Why can we not re-grow limbs? But can regrow/replace skin

50. Lizards can loose their tails when attacked by a predator
Will regrow their tails over time
Crayfish can regenerate claws, legs, antenne, but not eyes, why?