1. Chapter 12
The Cell Cycle

2. Why do cells divide?
The continuity of life is based on the reproduction of cells: cell division
Cells divide to:
Reproduce
Renewal
Repair
Replacement
Make new cells

3. Cell Cycle
The cell cycle is the entire life of the cell, including growing and reproducing.

4. Organization of Genetic Material
DNA: our genetic material, our genes
Chromatin: DNA and proteins
Chromosomes: thread-like structures in the nucleus that are made of chromatin
Genome: all of our DNA

5. Chromosome Duplication
Before a cell can divide, chromosomes must duplicate.
Each duplicated chromosome has two identical sister chromatids, attached at a centromere.

6. Phases of the Cell Cycle
Interphase: 90% of the cell’s life, during which growth, protein synthesis, and chromosome duplication occurs. Has 3 sub-phases:
G1 phase: “first gap” the cell grows
S phase: “synthesis” chromosomes duplicate
G2 phase: “second gap” the cell grows some more and prepares for division

7. Phases of the Cell Cycle
The other phase is the Mitotic Phase (M) during which the cell divides. It has 2 sub-phases:
Mitosis: when the nucleus divides
Cytokinesis: when the cytoplasm and the rest of the cell divides

8. Cell Cycle

9. The Mitotic Spindle
The mitotic spindle is made of microtubules and proteins which help move the chromosomes around.
It is made in the centrosome (an organelle)
Asters are short microtubules that extend out from the centrosome
Kinetochores are where the asters attach to chromosomes

10. The Phases of Mitosis Prophase (Prometaphase) Metaphase Anaphase
Telophase
Cytokinesis

11. Prophase
Chromatin condenses and can be seen in the microscope

12. Prometaphase The nuclear membrane breaks up
Microtubules begin to get into place around the chromosomes

13. Metaphase Longest phase (20 minutes!)
Chromosomes line up in the middle of the cell (metaphase plate)
Kinetochores connect centromeres to spindle poles

14. Anaphase Shortest phase (2-3 minutes)
Sister chromatids pull apart and begin to move to opposite sides of the cell

15. Telophase Two new nuclei (daughter nuclei) begin to form
New nuclear membranes begin to form

16. Cytokinesis
The cytoplasm of the parent cells divide to form 2 new daughter cells

17. Cytokinesis in Animals
In animals, a cleavage furrow forms to pinch the cell in two

18. Cytokinesis in Plants
In plant cells, a cell plate made of vesicles filled with cellulose, forms in between the two new cells to make a new cell wall.

19. Binary Fission
Prokaryotes (bacteria and Archea) reproduce by binary fission, meaning “division in half.”
Bacteria have one chromosome, which is a a big circle, which reproduce starting at the origin of replication.
After DNA is duplicated, the plasma membrane pinches inward and a new cell wall grows between the daughter cells.

20. Regulation of the Cell Cycle
The cell cycle is driven by molecular signals present in the cytoplasm, called the cell cycle control system.
Checkpoints in the cell cycle are critical point where the cell is told to “stop” or “go-ahead”
G1 checkpoint: “restriction point” if the cell is told to stop it goes to G0 non-dividing phase (like muscle and nerve cells)

21. Kinases and Cyclins
Kinases are enzymes that active or inactive proteins of the cell cycle
Cyclins are proteins that must be attached to kinases to be active; they are cyclin dependent kinases (Cdks)
MPF “maturation-promotion factor” triggers G2

22. How cells grow
Cells don’t grow if they are over-crowded, which is called density-dependent inhibition
Most cells are anchorage dependent which means that they must be attached to something to grow
Cancer cells are NEITHER of these things, they are cells growing out of control wherever they want.

23. Cancer
Cancer cells are cells that divide excessively and invade other tissues.
They do not heed the normal signals that regulate the cell cycle.

24. Cancer
When a normal cell becomes cancerous, this is called transformation.
If it stays at the original site, this is a benign tumor.
If it metastasizes, this means it moves to another tissue, which is what malignant tumors do.

25. Cancer Treatment Radiation: damages cancer cell DNA
Chemotherapy: toxic drugs interfere with the cell cycle of rapidly dividing cancer cells
Surgery: physically cut out the cancer cells