1. The Cell Cycle October 12, 2005

2. Cell Division Functions in Reproduction, Growth, and Repair

3. Genome = all of a cell’s DNA Chromosome = individual DNA molecule Chromatin = chromosomal DNA and its protein scaffold Sister chromatids = the two identical copies of a duplicated chromosome Centromere = the point of attachment for two sister chromatids Somatic cells = (most cells) have two copies of each chromosome (diploid) Gametes = (reproductive cells; sperm and eggs) have one copy of each chromosome (haploid) Important Terms (part one)

4. Cell cycle = the ordered sequences of events involving cell division Interphase = the main part of the cell cycle: G1 phase - cell prepares for DNA synthesis, usually grows in size S phase - DNA is duplicated G2 phase - cell checks fidelity of DNA replication, prepares for nuclear division Mitosis subphases - prophase, prometaphase, metaphase, anaphase, telophase Cytokinesis = division of cytoplasm More Important Terms Mitosis (M phase) = nuclear division

5. Mitosis (1)

6. Mitosis (2)

7. The mitotic spindle is composed of microtubules, and directs the alignment of chromosomes on the metaphase plate. During anaphase, the microtubules attached to each centromere to guide the movement of chromosomes toward spindle poles. The Mitotic Spindle

8. Polar Depolymerization of Microtubules and Movement of Non- Kinetochore Microtubules

9. Microfilaments contract to divide the cytoplasm. Plant cells are less flexible, because of the cell wall, and deposit cell wall material between the two daughter cells. Cytoplasmic Division

10. Mitosis (differential staining)

11. Mitosis in Growing Tissue

12. Binary Fission in Bacteria

13. Evolution of Mitosis

14. The cell’s place in the cell cycle is signaled by the presence or absence of cell cycle kinases. A growth signal leads to passage through the G 0 restriction point into G 1. The cell then executes a programmed series of steps that culminate in mitosis and cytokinesis. Cell Cycle Control

15. is an example of kinase control of the cell cycle. It is like a license that allows the cell to begin M phase of the cell cycle. MPF is a two-subunit enzyme. One subunit is Cdk (present during the whole cell cycle). The other subunit is a cyclin protein that builds up as M phase approaches. When the cyclin concentration is high enough, cyclin binds to Cdk, forming the MPF enzyme. MPF activity signals the start of mitosis. MPF

16. Normal cells are transformed to tumor cells when cell division is not controlled. Cancer cells are growth-factor independent. Cancer cells have escaped density-dependent inhibition. Most cancerous cells are destroyed by the immune system, but some cells progress from benign to malignant, and possibly to metastatic. Cancer

17. Cell Culture and Growth Factors

18. Density-dependent inhibition is a property of normal cells. Cancer cells lack this inhibition. Density-dependent Inhibition

19. Metastatic cancer cells spread throughout the body. Metastatic Cancer

20. The cell cycle is controlled at major checkpoints that will block: 1. During G1 prior to the entry to S stage 2. During S and G2 prior to the entry to M stage 3. During the M stage prior to the end of mitosis Summary Regulation of the cell cycle is largely through the action of kinases, often associated with regulatory subunits called cyclins. DNA damage or incomplete replication is a major reason the cell cycle is blocked. Failure to correct the problem usually leads to cell death. If cells do not die, the uncontrolled cell division may lead to tumors.