1. CHAPTER 12 – THE CELL CYCLE

2. SCIENCE STARTER What is the cell cycle?
Draw a circle and map out the stages of the cell cycle.
List the 5 stages of the cell cycle and give a brief summary of the events that occur in each stage.
The cell cycle is a series of events that cells go through as they grow and divide. It is the life of the cell from the time it is first formed from a dividing parent cell until its own division into two cells.
G1, S, G2, M (mitosis and cytokinesis)
G1 – Phase in which the cells do most of their growing. The cell increases in size and synthesizes new proteins and organelles.
S – Replication of DNA occurs
G2 –Molecules and organelles needed for cell division are produced. The cell is preparing to divide.
Mitosis – The division of the nucleus.
Cytokinesis – The division of the cytoplasm.

3. THE MITOTIC CELL CYCLE
Mitosis is a continuous process, but conventionally broken down into five subphases:
Prophase
Prometaphase
Metaphase
Anaphase
Telophase

4. STAGES OF MITOTIC CELL CYCLE: Prophase
During prophase, the first phase of mitosis, the duplicated chromosome condenses and becomes visible.

5. STAGES OF MITOTIC CELL CYCLE: Prophase
During prophase, the first phase of mitosis, the duplicated chromosome condenses and becomes visible.
Mitotic spindle forms. It is composed of microtubules between the two centrosomes.

6. STAGES OF MITOTIC CELL CYCLE: Prophase
During prophase, the first phase of mitosis, the duplicated chromosome condenses and becomes visible.
Mitotic spindle forms. It is composed of microtubules between the two centrosomes.
Centrosomes move apart, apparently propelled along the nuclear surface by lengthening of the microtubule bundles between them.

7. STAGES OF MITOTIC CELL CYCLE: Prophase
During prophase, the first phase of mitosis, the duplicated chromosome condenses and becomes visible.
Mitotic spindle forms. It is composed of microtubules between the two centrosomes.
Centrosomes move apart, apparently propelled along the nuclear surface by lengthening of the microtubule bundles between them.
The nucleolus disappears and nuclear envelope breaks down.

8. STAGES OF MITOTIC CELL CYCLE: Prometaphase
During prometaphase:
Nuclear envelope fragments

9. STAGES OF MITOTIC CELL CYCLE: Prometaphase
During prometaphase:
Nuclear envelope fragments
Spindle fibers extend from each pole toward the cell’s equator

10. STAGES OF MITOTIC CELL CYCLE: Prometaphase
During prometaphase:
Nuclear envelope fragments
Spindle fibers extend from each pole toward the cell’s equator
Each chromatid now has a kinetochore located at the centromere region

11. STAGES OF MITOTIC CELL CYCLE: Prometaphase
During prometaphase:
Nuclear envelope fragments
Spindle fibers extend from each pole toward the cell’s equator
Each chromatid now has a kinetochore located at the centromere region
Some kinetochore microtubules attach to the kinetochores

12. STAGES OF MITOTIC CELL CYCLE: Prometaphase
During prometaphase:
Nuclear envelope fragments
Spindle fibers extend from each pole toward the cell’s equator

13. STAGES OF MITOTIC CELL CYCLE: Metaphase
During metaphase, chromosomes move to the center of the cell and align their centromeres along the metaphase plate.

14. STAGES OF MITOTIC CELL CYCLE: Metaphase
During metaphase, chromosomes move to the center of the cell and align their centromeres along the metaphase plate.
Kinetochores of sister chromatids face opposite poles, so identical chromatids are attached to kinetochore fibers radiating from opposite ends of the parent cell.

15. STAGES OF MITOTIC CELL CYCLE: Anaphase
During anaphase, the centromeres are pulled apart and the sister chromatids separate to become individual chromosomes and move towards opposite poles of the cell.

16. STAGES OF MITOTIC CELL CYCLE: Anaphase
During anaphase, the centromeres are pulled apart and the sister chromatids separate to become individual chromosomes and move towards opposite poles of the cell.
Kinetochore microtubules shorten at the kinetochore end as chromosomes approach the poles.

17. STAGES OF MITOTIC CELL CYCLE: Anaphase
During anaphase, the centromeres are pulled apart and the sister chromatids separate to become individual chromosomes and move towards opposite poles of the cell.
Kinetochore microtubules shorten at the kinetochore end as chromosomes approach the poles.
Simultaneously, the poles of the cell move farther apart, elongating the cell.

18. STAGES OF MITOTIC CELL CYCLE: Telophase
During telophase, the chromosomes spread out into a loose tangle of chromatin.

19. STAGES OF MITOTIC CELL CYCLE: Telophase
During telophase, the chromosomes spread out into a loose tangle of chromatin.
A nuclear envelope re-forms around each cluster of chromosomes.

20. STAGES OF MITOTIC CELL CYCLE: Telophase
During telophase, the chromosomes spread out into a loose tangle of chromatin.
A nuclear envelope re-forms around each cluster of chromosomes.
The spindle breaks apart, and a nucleolus becomes visible in each daughter nucleus.

21. STAGES OF MITOTIC CELL CYCLE: Cytokinesis
By the end of telophase, cytokinesis has begun. The cytoplasm is divided and two separate daughter cells appear shortly after.

22. MEIOSIS
A variation of cell division that yields daughter cells that have half as many chromosomes as the parent cell
Occurs ONLY in the gonads (ovaries and testes)
Fertilization joins the gametes and doubles the chromosome number