1. TOPIC 2.5
CELL DIVISION

2. 2.5.1 Outline the Stages of the Cell Cycle
The stages include interphase (G1, S and G2), mitosis and cytokinesis
Important terms:
Mitosis= process of nuclear division
Cytokinesis= after mitosis this is the actual physical division of the cell (not part of mitosis)
Stage G1= period of cell growth and increase in number of organelles
Stage S= synthesis of DNA occurs (replication)
Stage G2= growth and preparation for mitosis

3. http://www. youtube. com/watch. v=Q6ucKWIIFmg http://www. youtube

4. Checkpoints in the cell cycle:
There are 3 checkpoints during the cell cycle where the cycle will stop if there is a problem:
during G1
end of G2
end of mitosis
The cell goes into G0 and will not reproduce

5. 2.5.2 Tumours are the result of uncontrolled cell division
Tumours can occur in any organ or tissue
Tumours are formed by immortal cancer cells
Cell division is controlled- only cells needed for growth and/or repair are produced through mitosis
Tumour repressor genes produce proteins which inhibit cell division
Proto-oncogenes are genes that produce proteins which stimulate growth and cell division
If mutations occur in these 2 genes cell division can become uncontrolled, resulting in a tumour

6. Anchorage, cell density, and chemical growth factors affect cell division
An organism must be able to control the timing of cell division
Anchorage dependence
Most animal cells must be in contact with a solid surface to divide
Density-dependent inhibition
Cells form a single layer
Cells stop dividing when they touch one another
Inadequate supply of growth factor causes division to stop

7. Cells anchor to dish surface and divide.
When cells have formed a complete single layer, they
stop dividing(density-dependent
Inhibition).
If some cells are scraped away, the remaining cells divide to fill the dish with a single layer
and then stop (density-dependent
inhibition).
After forming a
single layer,
cells have
stopped dividing.
Providing an additional supply of growth factors
Stimulates further cell division.

8. Growth factors signal the cell cycle control system
The cell cycle control system regulates the events of the cell cycle
If a growth factor is not released at three major checkpoints, the cell cycle will stop
G1 of interphase
G2 of interphase
M phase
G1 checkpoint G0
Control
system G1 S M G2
M checkpoint
G2 checkpoint

9. How a growth factor might affect the cell cycle control system
Cell has receptor protein in plasma membrane
Binding of growth factor to receptor triggers a signal transduction pathway
Molecules induce changes in other molecules
Signal finally overrides brakes on the cell cycle control system

10. Growth factor Plasma membrane Relay proteins Receptor protein
LE 8-9b
Growth factor
Plasma membrane
Relay
proteins
Receptor
protein
G1 checkpoint
Signal
transduction
pathway
Control
system G1 S M G2

11. Growing out of control, cancer cells produce malignant tumors
Cancer cells do not respond normally to the cell cycle control system
Divide excessively
Can invade other tissues
May kill the organism

12. Carcinogens Cancer causing agents
Certain types of radiation
ex. Ultraviolet light increases chance of skin cancer
Certain chemicals
viruses
Increase the chance of mutations or increase the effects of mutations which are already present

13. Some tumours are harmless = benign
ex. Warts
Some tumours are malignant and spread (metastasize) to other parts of the body
Treatments:
Surgical removal- before they grow and spread
Radiation therapy- nuclear radiation beam targeting a precise point to “burn” all cells in the area
Chemotherapy- chemicals that destroy all rapidly dividing cells by medication (includes hair, lining of gut, sperm production) many side-effects

14. If an abnormal cell avoids destruction by the immune system, it may form a tumor
Benign: abnormal cells remain at original site
Malignant: abnormal cells can spread to other tissues and parts of the body
Metastasis: spread of cancer cells through the circulatory system

15. Cell Cycle includes: interphase, mitosis and cytokinesis
2.5.3 Interphase of the cell cycle involves: protein synthesis, DNA replication, and an increase in organelles
Cell Cycle includes: interphase, mitosis and cytokinesis
Mitosis= nuclear division
Cytokinesis= division of the cell
Interphase includes: (about 90% of the cell cycle)
G1 or Gap 1- cell grows, replicates organelles, and perform normal cell activities
S or Synthesis- DNA replicates
G2 or Gap 2- cell continues to grow

16. Interphase
Used to be called the “resting phase”, but scientists realized that this is a very active phase of a cell’s life cycle
Many biochemical reactions
Transcription and translation
DNA replication
Replication of organelles
Growth
During G2 the number of chloroplasts and mitochondria increases
Cell cycle varies between different cells
Bacteria= 20 minutes skin cell= 14 days RBC= 4 months liver cell= days
The above times vary depending on conditions

17. 2.5.4 Describe the 4 phases of Mitosis
Mitosis = nuclear division
4 phases include: prophase, metaphase, anaphase and telophase PMAT
The purpose of mitosis= increase the # of cells without changing the genetic material
The 2 daughter cells which result are identical to each other and to the origin parent cell
When the cell is not dividing it is in interphase

18. Interphase Happens BEFORE Mitosis
G1 , S and G2
The cell grows, makes more organelles and replicates its DNA (replication happens in the S phase of interphase)
During interphase chromosomes are NOT visible, but appear as long stringy strands
DNA is called chromatin when it is loose
The DNA is wrapped around proteins
(histones) and looks like “beads on a string”
Prokaryotic cells DNA is “naked” (not associated with proteins

19. Prophase Chromosomes become visible (supercoiled)
Centrioles move to opposite poles
Spindles form
Nucleolus disappears
Nuclear membranes disappears
Each chromosome has an identical copy attached to it (sister chromatid) at the centromere

20. Metaphase Chromosomes move to the equator
Spindle microtubules attach to the centromeres

21. Anaphase Centromeres separate
Chromatids separate and move to opposite poles
Once the sister chromatids separate they are called chromosomes

22. Telophase Chromosomes have arrived at the poles Spindle disappears
Centrioles replicate (in animal cells)
Nuclear membrane reappears
Nucleolus becomes visible
Chromosomes uncoil and
become chromatin

23. Cytokinesis The division of the cell into two identical cells
This happens after mitosis
Different in plant and animal cells
Animal cells form a cleavage furrow and the cell pinches into two
Plant cells form a cell plate which becomes a cell wall

24. 2.5.5 Explain how mitosis produces two genetically identical nuclei
Result of mitosis = two nuclei
During S phase of interphase the chromosomes replicate (form an exact copy)
These copies are called sister chromatids
Sister chromatids separate during anaphase (so they are now called chromosomes)
They move to opposite poles and during telophase are surrounded by a nuclear membrane
SO the result is 2 nuclei identical to each other and the original

25. Mitosis Video Clip

26. 2.5.6 What processes of organisms involve mitosis???
Embryonic Development- we all started as one cell (a zygote or fertilised egg) and became multicellular by mitosis. As the number of cells increase, differentiation takes place by expressing some genes and not others
Replacement and repair- we are constantly replacing dead or damaged cells
Growth- as we grow and develop we need to add more cells to our body
Asexual Reproduction-production of identical cells by mitosis ex. Vegetative reproduction in some plants