1. The Cell Cycle
Chapter 12
Unit 4

2. Why Cells Divide For reproduction For growth For repair & renewal
asexual reproduction
For growth
For repair & renewal
replace cells that die from normal wear & tear or from injury

3. Chromosomes Duplicated chromosome
2 sister chromatids attached by a centromere

4. Cell Cycle Alternates between: Mitotic phase (M) Interphase:
(90% of cell cycle)
G1, S, G2

5. Mitosis Divided into five stages: Prophase Prometaphase Metaphase
Anaphase
Telophase

6. Prophase Nucleoli disappear Chromatin fibers condense
Mitotic spindle forms
Centrosomes (centrioles) move apart

7. Prometaphase Spindle fibers extend from poles to the equator
Kinetochore microtubules attach to kinetochore
Kinetochore: structure located on centromeres
Nonkinetochore microtubules interact with those from opposite poles
Nuclear envelope disappears

8. Metaphase Centrosomes are positioned at opposite poles
Chromosomes move to metaphase plate
Kinetochores attach to kinetochore microtubules

9. Anaphase Sister chromatids split apart and move toward poles
Poles move farther apart elongating the cell

10. Telophase Nucleoli reappear Daughter nuclei begin to form
Chromatin fibers uncoil
Spindle microtubules disappear

11. Cytokinesis Division of cytoplasm Animal Cells: cleavage furrow
Plant Cells: cell plate forms

14. Evolution of Mitosis Binary Fission Bacterial reproduction
single circular chromosome
no membrane-bound organelles

16. Regulation of Cell Cycle Control
Types of cells differ in pattern of cell division
Cell cycle control system: control point where stop/go signals regulate the cell cycle

17. Major Checkpoints G1 checkpoint
Controlled by cell size, growth factors, environment
Either completes cell cycle or goes into G0 Phase
Nerve, muscle cells stay at G0; liver cells called back
G2 checkpoint
Controlled by DNA replication completion, DNA mutations, cell size
M-spindle (Metaphase) checkpoint
Check microtubule attachment to chromosomes at kinetochores

18. Internal Regulatory Molecules
cyclin-dependent kinase, Cdk: protein enzyme controls cell cycle; active when connected to cyclin
Cyclins: proteins which attach to kinases to activate them; levels fluctuate in the cell cycle
MPF (maturation-promoting factor):
specific cyclin-Cdk complex which allows cells to pass G2 and go to M phase

19. External Regulatory Factors
Growth Factor: proteins released by other cells to stimulate cell division
Density-Dependent Inhibition: crowded cells normally stop dividing; cell-surface protein binds to adjoining cell to inhibit growth
Anchorage Dependence: cells must be attached to another cell or ECM to divide

21. Cancer Cells Do not stop growing and dividing
May make growth factors themselves
May have abnormal growth factor signaling system
stop dividing at random points in the cycle instead of at check points.

22. Tumors unregulated growing mass of cells
Benign tumor: if tumor remains at original site
Malignant tumor: invasive enough to impair normal function of one or more organs of the body

23. Metastasis
Cancer cells may separate from the original tumor and spread into other tissues