1. Cell Division & Mitosis

2. Cell Size
We need to use a microscope to see cells because cells are so small. Why can’t a cell be as big as a house or at least as big as a baseball?
Compare the two cells diagrammed below. For each cell, calculate the surface area, volume, and ratio of surface area to volume.
All sides measure 4 µm
All sides measure 8 µm

3. Surface Area to Volume Calculations
v = lwh
Small cell
v = 4x4x4
= 64 µm3
Big cell
v = 8x8x8
= 512 µm3
Surface Area
s = 6(lw)
s = 6(4x4)
= 96 µm²
s = 6(8x8)
= 384 µm²
Surface Area to Volume Ratio s/v
s/v = 96/64
= 1.5
S/v = 384/512
= 0.75

4. Questions Which cell has the greatest surface area?
Which cell has the greatest volume?
Which cell has the greatest ratio of surface area to volume?
In which cell would the surface area of the membrane most efficiently service the cytoplasm?

5. Cell Growth & Reproduction

6. Asexual Reproduction
Asexual reproduction : producing offspring from one parent
Passes on exact copy of genes
Mitotic cell division
Example: binary fission, spores, budding, cloning

7. Sexual Reproduction Sexual Reproduction – generally involves 2 parents
Each parent contributes genes to offspring  each individual has a different set of inherited traits from its parents
Allows variation of traits within a species
Fusion of gametes/sex cells/germ cells resulting from meiotic division

8. The Cell Cycle
G1 phase
M phase
S phase
G2 phase

9. The Cell Cycle
If the cell cycle was 24 hours long, the cell would be in interphase for about 23 hours and mitosis for about 1 hour.
Interphase
G1 – (gap 1) growth period
S – DNA synthesis (each chromosome is replicated)
G2 – (gap 2) growth period and preparation for mitosis (ie. The cell produces all of the enzymes needed for mitosis and the organelles replicate for cell division (cytokinesis)).

10. Mitosis
The process of nuclear division that ensures that each offspring (daughter cell) has a complete set of chromosomes in its nucleus
Once a cell reaches its maximum size it has two alternatives
Divide
Die
When a vital cell dies it must be replaced
Mitosis and cell division ensure that these cells are replaced

11. Cytokinesis
Once the « genetic material » has divided, the cytoplasm must also divide. This is called « CYTOKINESIS » and ensures equal distribution of the organelles.

12. The Genetic Code GENES are the units of heredity
The genetic code is the code that determines the inherited characteristics or traits of an organism. The code is passed from parent cells to daughter cells through cell division.
When preparing for cell division (Interphase), the genetic code is in the form of chromatin.
Chromatin are strands of unravelled DNA
Chromosomes are tightly coiled DNA strands

13. Binary Fission

14. Origin of Cell wall replication Plasma membrane E. coli cell Bacterial
Figure
Origin of
replication
Cell wall
Plasma
membrane
E. coli cell
Bacterial
chromosome 1
Chromosome
replication
begins.
Two copies
of origin
Figure Bacterial cell division by binary fission (step 1) 14

15. Origin of replication Cell wall Plasma membrane E. coli cell Bacterial
Figure
Origin of
replication
Cell wall
Plasma
membrane
E. coli cell
Bacterial
chromosome 1
Chromosome
replication
begins.
Two copies
of origin 2
One copy of the
origin is now at
each end of the
cell.
Origin
Origin
Figure Bacterial cell division by binary fission (step 2) 15

16. Origin of replication Cell wall Plasma membrane E. coli cell Bacterial
Figure
Origin of
replication
Cell wall
Plasma
membrane
E. coli cell
Bacterial
chromosome 1
Chromosome
replication
begins.
Two copies
of origin 2
One copy of the
origin is now at
each end of the
cell.
Origin
Origin 3
Replication
finishes.
Figure Bacterial cell division by binary fission (step 3) 16

17. Origin of replication Cell wall Plasma membrane E. coli cell Bacterial
Figure
Origin of
replication
Cell wall
Plasma
membrane
E. coli cell
Bacterial
chromosome 1
Chromosome
replication
begins.
Two copies
of origin 2
One copy of the
origin is now at
each end of the
cell.
Origin
Origin 3
Replication
finishes.
Figure Bacterial cell division by binary fission (step 4) 4
Two daughter
cells result. 17

18. (b) Diatoms and some yeasts
Figure 9.13
Chromosomes
Microtubules
Intact nuclear
envelope
(a) Dinoflagellates
Kinetochore
microtubule
Figure 9.13 Mechanisms of cell division
Intact nuclear
envelope
(b) Diatoms and some yeasts 18

19. Chromatin vs Chromosomes
Sister Chromatids
Centromere
Chromatin
Chromosome
Important: Sister chromatids carry identical genetic information

20. Chromosome Duplication
Duplication occurs during the S-phase of interphase to form a double-stranded chromosome
Distribution of the double-stranded chromosomes into two new daughter cells occurs during anaphase of mitosis

21. Growth & Cell Specialization Fission, Spores, Budding, Cloning
Cell Division & Growth
Cell Division & Reproduction 
Mitosis
Cell Cycle
Growth & Cell Specialization
Adult 
Assexual
Mitosis
Fission, Spores, Budding, Cloning 
Sexual
Meiosis 2n n
Gametes (n)
Sperm & Egg
Fertilization
Zygote

22. MITOSIS

23. Two sister chromatids of
G2 of Interphase
Prophase
Centrosomes
(with centriole
pairs)
Chromosomes
(duplicated,
uncondensed)
Early mitotic
spindle
Centromere
Aster
Figure 9.7c Exploring mitosis in an animal cell (part 3: G2 of interphase and prophase)
Plasma
membrane
Nucleolus
Nuclear
envelope
Two sister chromatids of
one chromosome 23

24. Prometaphase Metaphase Fragments of nuclear envelope Nonkinetochore
microtubules
Metaphase
plate
Figure 9.7d Exploring mitosis in an animal cell (part 4: prometaphase and metaphase)
Kinetochore
Kinetochore
microtubule
Spindle
Centrosome at
one spindle pole 24

25. Anaphase Telophase and Cytokinesis Cleavage furrow Nucleolus forming
Figure 9.7e Exploring mitosis in an animal cell (part 5: anaphase, telophase and cytokinesis)
Nuclear
envelope
forming
Daughter
chromosomes 25

26. 10 m
Figure 9.7f Exploring mitosis in an animal cell (part 6: G2 of interphase micrograph)
G2 of Interphase 26

27. 10 m
Figure 9.7g Exploring mitosis in an animal cell (part 7: prophase micrograph)
Prophase 27

28. 10 m
Figure 9.7h Exploring mitosis in an animal cell (part 8: prometaphase micrograph)
Prometaphase 28

29. 10 m
Figure 9.7i Exploring mitosis in an animal cell (part 9: metaphase micrograph)
Metaphase 29

30. 10 m
Figure 9.7j Exploring mitosis in an animal cell (part 10: anaphase micrograph)
Anaphase 30

31. Telophase and Cytokinesis 10 m
Figure 9.7k Exploring mitosis in an animal cell (part 11: telophase and cytokinesis micrograph)
Telophase and
Cytokinesis 31

32. Aster Centrosome Sister chromatids Metaphase plate (imaginary) Kineto-
chores
Microtubules
Chromosomes
Overlapping
nonkinetochore
microtubules
Figure 9.8 The mitotic spindle at metaphase
Kinetochore
microtubules
1 m
0.5 m
Centrosome 32

33. Chromosomes condensing Nucleus Nucleolus Chromosomes 10 m Prophase
Figure 9.11
Chromosomes
condensing
Nucleus
Nucleolus
Chromosomes
10 m 1
Prophase 2
Prometaphase
Cell plate
Figure 9.11 Mitosis in a plant cell 3
Metaphase 4
Anaphase 5
Telophase 33

34. Nucleus Chromosomes condensing Nucleolus 10 m Prophase 1 Figure 9.11a
Figure 9.11a Mitosis in a plant cell (part 1: prophase)
10 m 1
Prophase 34

35. Chromosomes 10 m Prometaphase 2 Figure 9.11b
Figure 9.11b Mitosis in a plant cell (part 2: prometaphase)
10 m 2
Prometaphase 35

36. Figure 9.11c
Figure 9.11c Mitosis in a plant cell (part 3: metaphase)
10 m 3
Metaphase 36

37. Figure 9.11d
Figure 9.11d Mitosis in a plant cell (part 4: anaphase)
10 m 4
Anaphase 37

38. Cell plate 10 m Telophase 5 Figure 9.11e
Figure 9.11e Mitosis in a plant cell (part 5: telophase)
10 m 5
Telophase 38

39. Interphase
Chromosomes are not clearly discerned in the nucleus, although a dark spot called the nucleolus may be visible.
The cell may contain a pair of centrioles (or microtubule organizing centers in plants) both of which are organizational sites for microtubules.

40. Prophase
Chromatin in the nucleus begins to condense and becomes visible in the light microscope as chromosomes.
The nucleolus disappears.
Centrioles begin moving to opposite ends of the cell and spindle fibres begin to appear.

41. Prometaphase
The nuclear membrane dissolves, marking the beginning of prometaphase.
Proteins attach to the centromeres creating the kinetochores.
Spindle fibres (microtubules) attach at the kinetochores and the chromosomes begin moving.

42. Metaphase
Spindle fibres align the chromosomes along the middle of the cell nucleus. This line is referred to as the equator.
This organization helps to ensure that in the next phase, when the chromosomes are separated, each new nucleus will receive one copy of each chromosome.

43. Anaphase
The paired chromosomes (sister chromatids) separate at the kinetochores and move to opposite sides of the cell.

44. Telophase
Chromatids arrive at opposite poles of cell, and new membranes form around the daughter nuclei.
The chromosomes unwind to form chromatin and are no longer visible under the light microscope.
The spindle fibres disappear.
Cytokinesis occurs.

45. Cytokinesis
In animal cells, cytokinesis results when a fiber ring composed of a protein called actin around the centre of the cell contracts pinching the cell into two daughter cells, each with one nucleus.
In plant cells, the rigid wall requires that a cell plate be synthesized between the two daughter cells

47. Figure 9.UN03
Figure 9.UN03 Test your understanding, question 6 47

48. Regulating the Cell Cycle

49. Controls on Cell Division
Cell growth is controlled
These controls can be turned on or off
Example: When you are cut in the skin or break a bone, the cells surrounding the injury will begin to divide. When healing is almost complete, mitosis will slow down and cell return to interphase and growth stops.

50. Anchorage Dependence
Most animal cells need to be in contact with a solid surface such as a growth medium in a petri dish (in vitro) or in the extracellular matrix of a tissue (in vivo) to divide

51. Density-Dependent Inhibition
Anchorage dependence: cells
require a surface for division
Density-dependent inhibition:
cells form a single layer
Density-dependent inhibition:
cells divide to fill a gap and
then stop
Figure 9.18 Density-dependent inhibition and anchorage dependence of cell division
20 m
20 m
(a) Normal mammalian cells
(b) Cancer cells 51

52. Growth Factors in Cell Division

53. Cell Cycle Regulators
Mitosis is triggered by a group of proteins called cyclins (growth factor)
Cyclins regulate the timing of the cell cycle in eukaryotic cells
Cyclins were the first of dozens of proteins to be discovered that are involved in controlling the cell cycle
Cyclins, in particular, rise in concentration just before mitosis and cause spindle fibres to form.

54. The effect of cyclin on a cell in G2
A sample is injected into a second cell in G2 of interphase.
A sample of cytoplasm is removed from a cell in mitosis.
As a result, the second cell enters mitosis.

55. External & Internal Regulators
Internal Regulators are proteins that respond to events occuring inside the cell.
Examples; some proteins prevent mitotic division until all chromosomes have been replicated while others prevent anaphase from starting until all of the chromosomes have been connected by spindle fibres.
External Regulators are proteins that respond to events outside the cell.
Examples; these proteins are found surrounding cells in embryonic development and around injured cells.

56. Control System in the Cell Cycle

57. Checkpoint System
What happens when a cell does not receive a go-ahead signal during the G1-phase?
The cell enters a G0 phase and no longer divide
Nerve cells enter the G0 phase very early on in animal development

58. Without go-ahead signal, cell enters G0. With go-ahead signal,
G1 checkpoint G0 G1 G1
Without go-ahead signal,
cell enters G0.
With go-ahead signal,
cell continues cell cycle.
Figure 9.16a Two important checkpoints (part 1: G1 checkpoint)
(a) G1 checkpoint 58

59. Without full chromosome attachment, stop signal is received.
M checkpoint G2
checkpoint
Anaphase
Prometaphase
Metaphase
Without full chromosome
attachment, stop signal is
received.
With full chromosome
attachment, go-ahead signal
is received.
Figure 9.16b Two important checkpoints (part 2: M checkpoint)
(b) M checkpoint 59

60. Signal Transduction Pathway Caused by Growth Factors

61. Cancer Cancer is the result of uncontrolled cell growth
Cancer cells do not respond to cell growth regulators the same way normal cells do. As a result cancer cells multiply uncontrollably therefore forming masses of cells called TUMOURS that can damage surrounding tissues.

62. Tumors
Two types:
Benign – cause problems by growing and distrupting surrounding organs, but can usually be completely removed through surgery
Malignant – cells spread into neighboring tissues and causes problems in organs that it spreads to (process is called metastasis)

63. Classes of Cancers
Carcinomas – originate in the external or internal coverings of the body
Sarcomas – occur in bone and muscle
Leukemias – bone marrow
Lymphomas – spleen and lymph nodes

64. Malignant Tumor 5 m Breast cancer cell (colorized SEM) Metastatic
Lymph
vessel
Tumor
Blood
vessel
Figure 9.19 The growth and metastasis of a malignant breast tumor
Glandular
tissue
Cancer
cell 1
A tumor grows
from a single
cancer cell. 2
Cancer cells
invade
neighboring
tissue. 3
Cancer cells spread
through lymph and
blood vessels to
other parts of the
body. 4
A small percentage
of cancer cells may
metastasize to
another part of the
body. 64

65. p53
The gene p53, which is the code for the protein that stops mitosis from occuring until chromosomes are all replicated, is often damaged in most forms of cancer.
Genes are damaged (mutated) by environmental factors such as
Tobacco
Radiation
Carcinogenic chemicals

66. Stem Cells Undifferentiated cells
Can develop into any type of cell in the body or into any type of a certain group of cells
Found in embryos, umbilical cords, bone marrow
The development of stem cell technology raises many ethical questions

67. Figure 9.1 How do a cell’s chromosomes change during cell division?