2. How do cells know when to divide?
Cell division can be turned on and off
Cyclins regulate the cell cycle
Family of proteins names after cyclin – the oroginal molecule discovered
This was just the start….
There is a whole host of regulatory proteins both inside and outside the cell

3. Internal vs External regulators
Internal regulators
Respond to events occurring inside a cell
Cell cycle only proceeds when certain events have happened
Ensure cell division only occurs after mitosis
Cells will not anaphase until the spindle fibers attach to the chromosome
External regulators
Direct cells to speed up or slow down cell cycle
Growth factors stimulate growth and division of cells
Important during wound healing, embryo development
Some regulators on neighbouring cells inhibit cell growth

4. Apoptosis As cells are produced other cells die
Cells can die due to damage or injury or
Cells can be programed to die – apoptosis
Once triggered leads to self destruction
Cell and chromatin shrink
Cell membrane breaks off
Neighboring cells clean up remains

5. What is cancer?
A condition where body cells become unable to control growth
Cancer cells do not respond to normal growth regulation signals
Cancer cells form a tumor
Benign tumors – does not spread to surrounding healthy tissue
Malignant tumors – invade and destroy surrounding healthy tissues
Tumor absorb nutrients needed by other cells, block nerve connections and prevent organs from functioning properly

6. What causes cancer? Defects in genes that regulate cell growth Smoking
Radiation
Other defective genes
Certain viral infections
Common factor – control over the cell cycle has broken down
Defect in p53 genes most common

7. Cancer treatment Tumors can be removed by surgery
As cancer cells replicate so quickly they are vulnerable to radiation damage
Carefully targeted beams of radiation can treat cancer
Chemotherapy – Chemical compounds that kill cancer cells/inhibit growth
But also effect normal healthy cells
Lots of side effects
Conquering cancer requires detail understanding of the cell cycle

8. Cell differentiation
Section 10.4

9. How do cells become specialized?
Humans have cells
Only 47 rounds of mitosis
All multicellular organisms have an embryonic stage
Over time cells get specialized for specific functions
Termed cell differentiation
Over development, cells differentiate into many types

10. Mapping differentiation
Differentiation determines a cells ultimate identity
In some organisms it’s role is determined by the cells development
In a microscopic worm, the outcome of every cell has been mapped out

11. Cell differentiation in mammals
The process is more flexible
Cell differentiation is controlled by a number of factors in the embryo
Adult cells however reach a point where their differentiation is complete
Can’t become new types of cells

12. Stem cells
Zygotes are totipotent ( they can literally become any body cell!)
After 4 days, an embryo forms into a blastocyst – a hollow ball of cells with a cluster of cells inside known as inner cell mass
Even this early cells have begun to specialize
Outer part attaches to the mother
Inner part becomes embryo

13. Stem cells
The inner cells are pluripotent – they can become any of the body’s cells – just not tissues that surround the embryo
Stem cells – undifferentiated cells from which all other cells develop

14. Adult vs Embryonic stem cells
Adult stem cells
Cells in tissues in an adult body need to be constantly replaced
Pools of adult stem cells found in various locations produce the new cells needed for these tissues
Example – blood cells from bone marrow, skin stem cells in hair follicles
Adult stem cells are multipotent – types of differentiated cells that can form are limited to the tissues where they are found
Embryonic stem cells
Pluripotent – can produce every cell in the body
Since 1998 they have been able to be grown in a culture in a lab

15. Benefits of stem cell research
Large potential for treating human conditions and diseases
Heart attack damage can be reversed using stem cell therapy
Same idea for brain damage, damage nerves, or repair organs damaged by chemicals or disease
Could lead to a new field of regenerative medicine
Damaged cells are replaced by new, undifferentiated cells

16. Ethical issues
Adult stem cells can be harvested from a willing donor – no real issues
Harvesting of embryonic stem cells generally will destroy the embryo
Some people argue that destruction of human embryonic life is unethical
Others argue that it is essential for saving human life
It is a controversial topic, as arguments for and against it involve ethical issues of life and death

17. Other approaches Understanding why stem cells are so versatile
Can artificial stem cells be made?
Proteins that bind to bind to DNA and activate genes (transcription factors) are used
Promising, but early stages of research
Other research has created ’artificial’ pluripotent cells from human fibroblast cells
May make it possible for treatments to be tailored to a patient by using their own cells