1. The Cell Cycle Chapter 12

2. When do cells divide?  Reproduction  Replacement of damaged cells  Growth of new cells  In replacement and growth cell divisions, how should daughter cells compare to parent cell?  The daughter cells should be identical copies of the parent cell

3. Functions of Cell Division

4. How can identical daughter cells form?  The genome must be copied and then divided such that each daughter cell gets one of the copies.  Genome = all the genes in an organism

5. Bacterial Reproduction  How do bacterial cells reproduce?

6. Important terms in eukaryotic cell division  Chromosome - threadlike structures that are composed of DNA and protein  Replication - process whereby DNA is identically copied (before cell division)  Mitosis - division of the nucleus  Cytokinesis - division of the cytoplasm  Chromatin - DNA and protein complex that is thin and fibrous; it will condense into distinct chromosomes during cell division

7. Important terms in eukaryotic cell division  Chromatid - after replication the chromosome consists of 2 sister chromatids joined at the centromere  Centromere - specialized region of the chromosome, where chromatids are joined. Each chromosome has one centromere

8. The Cell Cycle

9. Interphase  90% of cell cycle is spent in this phase  G 1 = first growth phase  S = synthesis phase, DNA synthesis (replication) occurs here  G 2 = second growth phase

10. G 2 phase of Interphase in animal cells  Nuclear envelope is visible  One or more nucleoli are present  Centrioles are replicated and the 2 pairs are near nucleus  Aster forms around each pair of centrioles  Chromosomes are loosely packed into chromatin fiber, not distinguishable

11. General Overview of Mitosis

12. Prophase:  In the Nucleus:  Nucleoli disappear  Chromosome fibers condense into discrete chromosomes  Each chromosome consists of 2 sister chromatids joined at the centromere

13.  In the Cytoplasm:  Mitotic spindle begins to form  Spindle consists of microtubules arranged between the centrosomes  Centrosomes move apart due to lengthening of microtubules

14. Prometaphase:  Nuclear envelope breaks apart  Each chromatid has specialized structure called kinetochore located at the centromere region  Kinetochore microtubules interact with chromosomes at the kinetochore region  The kinetochore microtubles cause the chromosomes to move  Nonkinetochore microtubules radiate from each pole

15. Metaphase  Chromosomes move to the metaphase plate and line up there  The centromeres of the chromosomes are all aligned on the metaphase plate  Each sister chromatid of one chromosome, has a kinetochore microtubule attached to it from opposite poles  Kinetochore microtubules + nonkinetochore microtubules = spindle fiber

16. Anaphase  Kinetochore microtubules shorten and non-kinetochore microtubules lengthen  Centromeres divide and each chromosome has no sister chromatid component  The shape of the cell elongates into an ellipse  Chromosomes are pulled to the opposite poles

17. Telophase  Nonkinetochore microtubules continue to elongate the cell  New daughter nuclei form at the two poles  New nuclear envelopes are formed around the chromosomes  Nucleoli reappear  Chromosomes uncoil into chromatin fiber  Last phase of mitosis

18. Cytokinesis  Begins before telophase has completed  Evidenced by cleavage furrow in animal cells and cell plate in plant cells

21. Evolution of mitosis: Bacterial cells Dinoflagelates; chromosomes attach to nuclear envelope.

22. Diatoms; nuclear envelope stays, microtubules inside nucleus Most other eukaryotes; spindle forms outside of nucleus, and nuclear envelope breaks apart

23. Cytoplasmic Cell Signals in Regulation of Cell Cycle

24. Checkpoints in the cell cycle: If it passes the G 1 checkpoint cell divides -if not, enters G 0 phase and does not divide

25. Cyclin protein levels fluctuate according to cell cycle stage. When cyclin is high the Cdk attaches and phosphorylation leads to breakdown of nuclear envelope. Later MPF initiates cyclin breakdown

26. Cancer cells  How does abnormal cell division of cancer cells differ from normal cell division?  Cancer cells are not under density dependent inhibition  Continue to grow until all nutrients are used up  Cancer cells are immortal, do not shorten telomeres