1. Cell Division 1.6

2. Essential Idea: Cell division is essential but must be controlled.
1.6
Cell Division
Understandings:
Mitosis is division of the nucleus into two genetically identical daughter nuclei
Chromosomes condense by supercoiling during mitosis
Cytokinesis occurs after mitosis and is different in plant and animal cells
Interphase is a very active phase of the cell cycle with many processes occurring in the nucleus and cytoplasm
Cyclins are involved in the control of the cell cycle
Mutagens, oncogenes and metastasis are involved in the development of primary and secondary tumors
Application:
The correlation between smoking and incidence of cancers
Skills:
Identify the phases of mitosis
Determine the mitotic index from a micrograph

3. Interphase
G1 – growth, normal cell functions (protein synthesis, cellular respiration, metabolism, etc.)
S – DNA Replication
C. G2 – normal cell functions, growth, and prep for division (organelles increase in number, DNA begins to condense from chromatin to chromosomes, microtubules may begin to form)

4. II. Checkpoints – cell cycle pauses until allowed to proceed 1
II. Checkpoints – cell cycle pauses until allowed to proceed 1. Cyclins – proteins that control the cells progression through the cell cycle a. Bind to cyclin-dependent kinases (CDKs) which enable the cyclins to act as enzymes

5. III. Mitosis – Nuclear division (Actually a continuum but we describe as distinct phases)

6. Prophase
1. Chromosomes condense – supercoiling tightly around histones
2. Nucleolus breaks down
3. Microtubules grow from microtubule organizing centers (MTOCs)

7. 5. Centrosomes move toward opposite poles
4. Nuclear envelope breaks down
5. Centrosomes move toward opposite poles
6. Spindle fibers attach to kinetochore at centromeres

8. Metaphase
1. Centrosomes reach opposite poles
2. Spindle microtubules pull on chromosomes causing them to line up single-file on the metaphase plate (equator of cell)

9. Anaphase – (shortest phase)
1. Cell elongates due to pushing and pulling of microtubules
2. Microtubules shorten, pulling sister chromatids apart

10. Chromatids move to opposite poles – centromeres 1st
At end of anaphase, each pole has a complete, identical set of chromosomes

11. Telophase
1. Nuclear membrane starts to re-form
2. Chromosomes de-condense
3. Nucleolus reappears
4. Spindle apparatus disintegrates

12. IV. Cytokinesis A. Animal cells – pinches inward forming a cleavage furrow B. Plant cells – cell plate forms in middle

13. V. Cancer A. Cell cycle is out of control B
V. Cancer A. Cell cycle is out of control B. Results in a mass of abnormal cells (tumor) 1. Primary tumor – original location 2. Secondary = metastasis – spreads to other location(s)

14. Oncogenes – mutations in these genes contribute to normal cells becoming cancerous
Can be triggered by outside agents
Sun, chemicals, smoke