Cell Division and Mitosis

1. Cell Division and Mitosis Starr/Taggart’s Biology: The Unity and Diversity of Life, 9e Chapter 9

2. Key Concepts: • Continuity of life depends on reproduction • After cell division, each daughter cell must receive the same amount of DNA • The cell cycle: Interphase and Mitosis • DNA and proteins make up chromosomes in eukaryotic cells • Members of the same species have the same number of chromosomes in their cells

3. Key Concepts: • The body cells of many organisms have a diploid chromosome number • Mitosis keeps the chromosome number constant • Mitosis is the basis of growth and tissue repair in multicelled eukaryotes. • Single-celled eukaryotes and many multicelled eukaryotes reproduce by mitosis

4. Overview • DNA contains hereditary instructions • Before cells reproduce, they must undergo nuclear division • Mitosis • Meiosis • Multicelled organisms grow and repair themselves by mitosis

5. Overview • Mitosis and meiosis are nuclear division mechanisms • Mitosis in somatic cells allows growth, repair, and asexual reproduction • Meiosis occurs in germ cells, produces gametes, allows sexual reproduction • Prokaryotic cells reproduce asexually

6. Chromosomes • Each chromosome duplicates in preparation for mitosis • Sister chromatids remain attached

7. Mitosis and Chromosome Number • Chromosome number = Total of chromosomes in somatic cells • Humans 46 • Gorillas 48 • Pea plants 14 • Chromosomes are in pairs • Humans 23 pairs • 2n “diploid” • 1n “haploid” (gametes)

8. The Cell Cycle • A diploid cell produces two diploid daughter cells • Two phases in cell cycle • Interphase • Longest phase • Increase in mass, doubles components, and duplicates DNA • Mitosis • Nuclear division

9. Interphase • G1 • “Gap” - cell growth before DNA replication • S • “Synthesis” - DNA replication • G2 • “Second Gap” - preparation for division • The length of each part differs among different cell types

10. The Cell Cycle

11. Mitosis • Four stages • Prophase • Metaphase • Anaphase • Telophase • Cytokinesis • Cytoplasmic division

12. Prophase • Chromosomes become visible • Spindle apparatus forms • Centrioles move apart to opposite poles • Microtubules break apart into tubulin subunits • New tubulin subunits form the spindle • Nuclear envelope breaks up

13. Prophase

14. Metaphase • Chromosomes interact with microtubules on spindle apparatus • Attachment at centromeres • Kinetochore • Tubules pull on chromosomes • Orientation of sister chromatids to opposite poles • Alignment of chromosomes midway between the poles

15. Metaphase

16. Anaphase • Separation of sister chromatids • Movement toward opposite poles

17. Separation of Sister Chromatids • Microtubules attached to centromeres shorten and pull chromosomes towards poles

18. Separation of Sister Chromatids • Spindle elongates and the spindle poles are pushed farther apart by overlapping microtubules

19. Telophase • Chromosomes arrive at spindle poles • Chromosomes return to threadlike forms • New nuclear membranes form • Two nuclei form • Cytokinesis • Division of cytoplasm • Forms two cells

20. Metaphase to Interphase

21. Cytoplasmic Division • Cytokinesis • Between late anaphase and end of telophase • In plants: cell plate forms • Vesicles fuse • In animals: cleavage • Cleavage furrow - depression forms at cell’s midsection

22. In Conclusion • A parent cell provides each daughter cell with hereditary instructions • Eukaryotes divide by mitosis or meiosis and prokaryotes divide by binary fission • Each chromosome is one DNA molecule with proteins attached • Cells with a diploid number (2n) contain two of each kind of chromosome

23. In Conclusion • Mitosis maintains the chromosome number from one cell generation to the next • Mitosis is the basis of growth and tissue repair, and asexual reproduction in some eukaryotes • The cell cycle includes interphase and mitosis • The phases of mitosis are prophase, metaphase, anaphase, and telophase • developed by M. Roig