1. Chapter 12 – The Cell Cycle

2. Cell Division: Key Roles
Genome: cell’s genetic information
Somatic (body cells) cells
Gametes (reproductive cells): sperm and egg cells
Chromosomes: DNA molecules
Diploid (2n): 2 sets of chromosomes (humans = 46)
Haploid (1n): 1 set of chromosomes (humans = 23)
Chromatin: DNA-protein complex
Sister chromatids: replicated strands of a chromosome
Centromere: narrowing “waist” of sister chromatids
Mitosis: nuclear division
Cytokinesis: cytoplasm division
Meiosis: gamete cell division

3. The Cell Cycle Interphase (90% of cycle) Mitotic phase
G1 phase - growth
S phase - synthesis of DNA
G2 phase - preparation for cell division
Mitotic phase
Mitosis - nuclear division
Cytokinesis – cytoplasm division

4. Late Interphase (G2)

5. Mitosis

6. Mitosis

7. Mitosis Prophase Prometaphase Metaphase Anaphase Telophase
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8. Animal Mitosis Overview

9. Prophase Chromosomes visible Nucleoli disappear Sister chromatids
Mitotic spindle forms
Centrosomes move

10. Prophase

11. Prometaphase Nuclear membrane fragments
Spindle interaction with chromosomes
Kinetochore develops

12. Mitotic Spindle
Centrosome – organizes the cells microtubules (also called microtubule organizing center)
Aster – radial array of microtubules extends from each centrosome
Kinetochore – on sister chromatids near centromere, have attachment points for microtubules called kinetochore microtubules
Spindle positions chromosomes on metaphase plate

13. Prometaphase

14. Metaphase Centrosomes at opposite poles Centromeres are aligned
Kinetochores of sister chromatids attached to microtubules (spindle)

15. Metaphase

16. Anaphase Paired centromeres separate; sister chromatids liberated
Chromosomes move to opposite poles
Each pole now has a complete set of chromosomes

17. Anaphase

18. Chromosome Movement How do chromosomes move towards the poles?
Kinetochore fibers shorten at chromosome
Are broken down and removed as tubulin subunits

19. Telophase Daughter nuclei form Nuclear envelopes arise
Chromatin becomes less coiled
Two new nuclei complete mitosis

20. Telophase

21. Cytokinesis Cytoplasmic division Animals: cleavage furrow
Plants: cell plate

22. Cytokinesis

23. Binary Fission Cell division in a prokaryote
Much simpler than mitosis because prokaryotes lack a nucleus and only have 1 chromosome

24. Cell Cycle Regulation
Cell cycle control system – a series of checkpoints with go ahead and stop signals (usually a stop sign that needs to be overridden by a go-ahead signal)
Checkpoints at G1, G2, and M
At G1 checkpoint could be directed into G0 phase – most cells in G0, but many can be “called back” into the cell cycle, others cannot (nerve, muscle)

25. Cancer When cells lose control of their cell cycle
These cells divide excessively and invade other tissues, potentially shutting them down
Metastasis – the spread of cancer cells to locations distant from their origin