1. The Cell Cycle

2. In unicellular organisms, division of one cell reproduces the entire organism In unicellular organisms, division of one cell reproduces the entire organism Multicellular organisms depend on cell division for: Multicellular organisms depend on cell division for: Development from a fertilized cell Development from a fertilized cell Growth Growth Repair Repair Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

3. Cell division results in genetically identical daughter cells Most cell division (mitosis) results in daughter cells with identical genetic information, DNA Most cell division (mitosis) results in daughter cells with identical genetic information, DNA A special type of division (meiosis) produces nonidentical daughter cells (gametes, or sperm and egg cells) A special type of division (meiosis) produces nonidentical daughter cells (gametes, or sperm and egg cells) Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

4. Cellular Organization of the Genetic Material All the DNA in a cell constitutes the cell’s genome All the DNA in a cell constitutes the cell’s genome A genome can consist of A genome can consist of a single DNA molecule (prokaryotic cells) a single DNA molecule (prokaryotic cells) a number of DNA molecules (eukaryotic cells) a number of DNA molecules (eukaryotic cells) DNA molecules in a cell are packaged into chromosomes DNA molecules in a cell are packaged into chromosomes Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

5. Every eukaryotic species has a characteristic number of chromosomes in each cell nucleus Every eukaryotic species has a characteristic number of chromosomes in each cell nucleus Somatic cells (nonreproductive cells) have two sets of chromosomes Somatic cells (nonreproductive cells) have two sets of chromosomes Gametes (reproductive cells: sperm and eggs) have half as many chromosomes as somatic cells Gametes (reproductive cells: sperm and eggs) have half as many chromosomes as somatic cells Eukaryotic chromosomes consist of chromatin, a complex of DNA and protein (histones). Eukaryotic chromosomes consist of chromatin, a complex of DNA and protein (histones). Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

6. Distribution of Chromosomes During Eukaryotic Cell Division Each duplicated chromosome has two sister chromatids, which separate during cell division Each duplicated chromosome has two sister chromatids, which separate during cell division The centromere is where the two chromatids are most closely attached The centromere is where the two chromatids are most closely attached Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

7. Fig. 12-4 0.5 µm Chromosomes Chromosome duplication (including DNA synthesis) Chromo- some arm Centromere Sister chromatids DNA molecules Separation of sister chromatids Centromere Sister chromatids

8. Eukaryotic cell division consists of: Eukaryotic cell division consists of: Mitosis, the division of the nucleus Mitosis, the division of the nucleus Cytokinesis, the division of the cytoplasm Cytokinesis, the division of the cytoplasm Gametes are produced by a variation of cell division called meiosis Gametes are produced by a variation of cell division called meiosis Meiosis yields nonidentical daughter cells that have only one set of chromosomes, half as many as the parent cell Meiosis yields nonidentical daughter cells that have only one set of chromosomes, half as many as the parent cell Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

9. Phases of the Cell Cycle The cell cycle consists of The cell cycle consists of Interphase (cell growth and copying of chromosomes in preparation for cell division) Interphase (cell growth and copying of chromosomes in preparation for cell division) G 1 phase- cell grows G 1 phase- cell grows S phase- chromosomes duplicate S phase- chromosomes duplicate G 2 phase- cell grows/prepare for division G 2 phase- cell grows/prepare for division Mitotic (M) phase Mitotic (M) phase mitosis mitosis cytokinesis cytokinesis Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Video: MITOSIS

10. Fig. 12-UN1 Telophase and Cytokinesis Anaphase Metaphase Prometaphase Prophase MITOTIC (M) PHASE Cytokinesis Mitosis S G1G1 G2G2

11. Mitosis is conventionally divided into five phases: Mitosis is conventionally divided into five phases: Prophase Prophase Prometaphase Prometaphase Metaphase Metaphase Anaphase Anaphase Telophase Telophase Cytokinesis: (division of cytoplasm) Cytokinesis: (division of cytoplasm) Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

12. PROPHASE Chromatids condense and become visible Chromatids condense and become visible Nucleoli dissapears Nucleoli dissapears Centrosomes (pair of centrioles) move to the poles Centrosomes (pair of centrioles) move to the poles Spindle begins to form Spindle begins to form

13. PROMETAPHASE Nuclear envelope breaks Nuclear envelope breaks Microtubules form from centrosome and move toward the middle of cell Microtubules form from centrosome and move toward the middle of cell Sister chromatids have a kinetochore (specialized protein located on centromere) Sister chromatids have a kinetochore (specialized protein located on centromere) Spindle attach to kinetochore Spindle attach to kinetochore

14. METAPHASE Longest stage of mitosis Longest stage of mitosis Spindle is completely formed Spindle is completely formed Spindle attaches to kinetochore of chromatids Spindle attaches to kinetochore of chromatids Spindle moves chromatids to middle of cell (metaphase plate) Spindle moves chromatids to middle of cell (metaphase plate)

15. ANAPHASE Shortest stage of Mitosis Shortest stage of Mitosis Spindle pulls sister chromatids apart (become chromosomes) Spindle pulls sister chromatids apart (become chromosomes) Chromosomes are pulled toward the poles Chromosomes are pulled toward the poles Spindle shortens and cell elongates Spindle shortens and cell elongates Chromosomes reach poles Chromosomes reach poles

16. TELOPHASE Nuclear envelopes reappear Nuclear envelopes reappear Spindle dissappears Spindle dissappears 2 identical nuclei and 1 cytoplasm 2 identical nuclei and 1 cytoplasm Video: MITOSIS

17. Cleavage furrow Contractile ring of microfilaments Daughter cells (a) Cleavage of an animal cell (SEM) (b) Cell plate formation in a plant cell (TEM) Vesicles forming cell plate Wall of parent cell Cell plate Daughter cells New cell wall Cytokinesis: A Closer Look Division of cytoplasm Division of cytoplasm In animal cells, cytokinesis occurs by a process known as cleavage, forming a cleavage furrow In animal cells, cytokinesis occurs by a process known as cleavage, forming a cleavage furrow In plant cells, a cell plate forms during cytokinesis In plant cells, a cell plate forms during cytokinesis

18. The Cell Cycle Control System The sequential events of the cell cycle are directed by a distinct cell cycle control system, which is similar to a clock The sequential events of the cell cycle are directed by a distinct cell cycle control system, which is similar to a clock The clock has specific checkpoints where the cell cycle stops until a go-ahead signal is received The clock has specific checkpoints where the cell cycle stops until a go-ahead signal is received Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Video: CONTROL SYSTEM CELL CYCLE Video: CELL CYCLE

19. S G1G1 M checkpoint G2G2 M Control system G 1 checkpoint G 2 checkpoint

20. Cell receives a go-ahead signal at the G 1 checkpoint, it will usually complete the S, G 2, and M phases and divide Cell receives a go-ahead signal at the G 1 checkpoint, it will usually complete the S, G 2, and M phases and divide Cell does not receive the go-ahead signal, it will exit the cycle, switching into a nondividing state called the G 0 phase Cell does not receive the go-ahead signal, it will exit the cycle, switching into a nondividing state called the G 0 phase Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings G0G0 Cell does not receive a go-ahead signal Cell receives a go-ahead signal G 1 checkpoint G1G1 G1G1