1. Cell Division Chapter 9 Lecture Outline

2. © 2009 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 4/e 2 The Need for Cell Division Renewal and repair of tissues Stem cells capable of self-renewal give rise to descendant cells Asexual and sexual reproduction Prokaryotes divide through binary fission Eukaryote cell division is more complicated

3. © 2009 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 4/e 3 Cell cycle: Two Main Stages Cell cycle  Series of events in life cycle of a cell  Time to complete cell cycle Dependent on organism, type of cell, life stage  Two main stages Interphase  Most cells spend 90% of lifespan in this stage Cell division  Mitosis and cytokinesis

4. © 2009 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 4/e 4 Interphase: The Longest Stage The period between divisions  Longest phase of the cell cycle  The cell prepares to divide Divided into 3 stages:  G 1 : growth after mitosis  S: synthesis of DNA  G 2 : growth before mitosis

5. © 2009 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 4/e 5 The Cell Cycle

6. G 1 and G 2 phases G stands for “gap”  Early biologists saw a gap Between S phase and cell division  Important for two reasons periods of growth  size of cell and protein content increase preparation for next phase  checkpoint that ensures conditions are suitable © 2009 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 4/e 6

7. 7 G 0 Phase Most cells are not actively dividing These cells are in G 0 phase  Can last days to years  Some cells will divide again; e.g. liver cells  Some cells stay in G 0 ; e.g. nerve cells

8. © 2009 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 4/e 8 DNA Packaged as Chromosome DNA molecules are enormously long  Double helix nearly 2 meters in length DNA is tightly packaged with proteins Chromatin  DNA and proteins Chromosome  Tightly packed

9. © 2009 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 4/e 9 Karyotype Chromosomes are visible during mitosis Their number and shape can be studied Humans have 46 chromosomes

10. © 2009 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 4/e 10 Homologous Chromosomes 46 chromosomes are arranged in 23 pairs  One came from each parent 22 pairs are autosomes  Both chromosomes are homologues 1 pair are sex chromosomes  Can be homologous; XX for females  Can be different; XY for males

11. © 2009 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 4/e 11 Mitosis Consists of five phases  Prophase  Prometaphase  Metaphase  Anaphase  Telophase Cytokinesis: division of the cytoplasm

12. © 2009 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 4/e 12 Prophase Cell enters mitosis  Chromosomes condense  Centrosomes move apart Go to the poles of the cell  Mitotic spindle begins to form

13. © 2009 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 4/e 13 Prometaphase Mitosis proceeds  Chromosome condensation completed  Nuclear envelope breaks down  Mitotic spindle extends from centrosomes Attaches to centromeres of chromosomes Kinetochore: site of attachment Chromatids linked to opposite poles

14. © 2009 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 4/e 14 Metaphase Chromosomes line up  Metaphase plate  Align sister chromatids Equal and balanced segregation

15. © 2009 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 4/e 15 Anaphase Chromatids separate  Break free and dragged to opposite sides Microtubules shorten Result:  Equal segregation of chromosomes in two daughter cells

16. © 2009 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 4/e 16 Telophase and Cytokinesis Telophase:  Chromosomes reach the poles  Mitotic spindle falls apart  Chromosomes unfold  Nuclear membrane reforms Cytokinesis  Cytoplasm is divided  Two cells are formed

17. © 2009 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 4/e 17 Mitosis

18. © 2009 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 4/e 18 Meiosis Used to make gametes  Eggs and sperm Chromosome number is halved (haploid) Zygote is diploid after fertilization Meiosis Fertilization Mitosis

19. © 2009 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 4/e 19 Meiosis I vs. Mitosis Sister Chromatids separate Sister Chromatids remain attached

20. © 2009 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 4/e 20 Meiosis II MetaphaseAnaphase

21. © 2009 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 4/e 21 Which of the following is not true about interphase? A.The cell grows larger during interphase. B.Chromosomes are duplicated during interphase. C.Interphase is divided into three phases. D.Chromosomes segregate to daughter cells during interphase. Concept Quiz

22. © 2009 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 4/e 22 Which of the following is true about homologous chromosomes? A.Both were received from the same parent. B.One of each segregates to each daughter cell during mitosis. C.Both stay together in meiosis I. D.All 23 pairs are always homologous. Concept Quiz

23. © 2009 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 4/e 23 Meiosis insures that A.Each gamete receives the same genes B.Chromosome number is doubled in the gametes C.Zygotes produced by fertilization have the normal number of chromosomes D.All paternal chromosomes end up in the same gamete Concept Quiz

24. Biology In the News “New Type of Stem Cells May Help Regenerate Heart Tissues”  Induced pluripotent stem cells A genetically reprogrammed adult body cell Behaves like pluripotent embryonic stem cells © 2009 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 4/e 24

25. Terms Chromatin Chromosome Crossing-over Cytokinesis Diploid DNA segregation Fertilization G 0 phase G 1 phase G 2 phase Gametes Genetic recombination Haploid Homologous pair Homologues Independent assortment Interphase Karyotype © 2009 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 4/e 25

26. Terms Kinetochores Maternal homologue Meiosis Meiosis I Meiosis II Metaphase Mitosis Mitotic spindle Paternal homologue Prometaphase Prophase S phase Sex chromosomes Sexual reproduction Sister chromatids Somatic cells Stem cells Telophase © 2009 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 4/e 26

27. © 2009 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 4/e 27 Process Animation 9.1 The Cell Division Cycle  Macintosh Macintosh  Windows Windows

28. © 2009 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 4/e 28 Process Animation 9.2 Mitosis and Cell Division  Macintosh Macintosh  Windows Windows

29. © 2009 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 4/e 29 Process Animation 9.3 Meiosis  Macintosh Macintosh  Windows Windows

30. Discover Biology StudySpace http://www.wwnorton.com/college/biology/discoverbio4 30

31. Additional Art from Chapter 9 All art files from the book are available in JPEG and PPT formats on the Instructor Resource Disc 31

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