1. Cell Growth & Division
Biology  Pearland ISD

2. Cell Division There are 2 main reasons cell divides:
The cell has more trouble trying to move nutrients and wastes across the cell membrane.
The larger a cell becomes, the greater the demand it puts on its DNA.
Bottom line – cells need to be replaced

3. Cell Cycle The sequence of growth and division of a cell
An average cycle may be 22 hours
Three general periods:
resting phase
growth phase
division phase

4. G0 (Resting phase) Non-dividing, differentiated state.
Most human cells are in G0 phase.
Liver cells:
Generally in G0, but can be “called back” to cell cycle by external cues.
Nerve & muscle cells:
Highly specialized.
Arrested in G0 & can never divide.

5. Interphase (Growth phase)
Most of the cell’s life is spent in interphase
Longest phase –(90% of cell’s growth)
Centrioles – help to organize cell division Chromatin – DNA bound protein within the nucleus

6. Interphase (Growth phase)
New DNA is formed during 3 phases:
G1 – 1st period of growth
1. Increase in size.
2. Makes new proteins and
organelles.
S – DNA is synthesized or replicated
1. Chromosomes are replicated.
2. New DNA molecules are made.
G2 – final cell growth
1. Shortest phase
2. Prepares cell for mitosis

7. Terms to know
Chromosome – contains genetic information (DNA) passed from one generation to the next
Spindle – microtubule that helps separate chromosomes
A – centromere: center of chromosome B – chromatids: two identical “sister” parts of the chromosome

8. Takes place within the nucleus of the cell.
Mitosis
Takes place within the nucleus of the cell.

9. Mitosis (Division phase)
4 Phases:
(PMAT)
Prophase
Metaphase
Anaphase
Telophase

10. 4 phases that blend from one to another

11. Prophase 1st and longest phase of mitosis Chromatin become chromosomes
Chromatids are joined by centromere
Nucleus disappears
Centrioles migrate to poles
Spindles are formed

12. Metaphase 2nd phase of mitosis Chromosomes meet in the middle of cell
Pulled by spindles
Each chromosome is attached to top of spindle

13. Anaphase 3rd phase of mitosis Centromeres are split apart
Chromatids are pulled apart and begin to drift to opposite poles

14. Telophase Final phase of mitosis Begins when chromatids reach poles
New nucleus starts to form
Chromosomes start to unwind
Spindles disappear
Cytoplasm begins to divide

15. Cytokinesis Cytoplasm pinches in half
Each daughter cell has an identical set of chromosomes

19. Cancer Cancer is a disorder where the cell has uncontrolled growth.
Cancer cells do NOT respond to regulators.
This causes the cells to form masses called tumors, which can damage surrounding tissues.

22. Cancer Development
Cancer develops only after a cell experiences ~6 key mutations (“hits”).
Unlimited growth
Turn ON growth promoter genes.
Ignore checkpoints
Turn OFF tumor suppressor genes.
Escape apoptosis
Turn OFF suicide genes.
Immortality = unlimited divisions
Turn ON chromosome maintenance genes.
Promotes blood vessel growth
Turn ON blood vessel growth genes.
Overcome anchor & density dependence
Turn OFF touch-sensor gene.

23. Cancer Triggers Mutations in cells can be triggered by: UV radiation
Chemical exposure
Radiation exposure
Heat
Cigarette smoke
Pollution
Age
Genetics

25. 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.

26. 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

27. Cancers are named according to location of origin:
Carcinoma: external or internal body coverings
Sarcoma: tissues that support the body
Leukemia and lymphoma: blood-forming tissues
Radiation and chemotherapy are effective as cancer treatments because they interfere with cell division