1. Chapter 12 The Cell Cycle

2.  The continuity of life  Is based upon the reproduction of cells, or cell division

3. The Cell Cycle  Unicellular organisms  Reproduce by cell division

4. The Cell Cycle  Multicellular organisms depend on cell division for  Development from a fertilized cell  Growth  Repair Growth and development Tissue renewal

5. Cell Division  Cell division results in genetically identical daughter cells  Cells duplicate their total genetic material (genome)  Before they divide, ensuring that each daughter cell receives an exact copy of the genetic material, DNA

6. Genetic Material  Eukaryotic chromosomes  Consist of chromatin, a complex of DNA & protein that condenses during cell division

7. Genetic Material  The DNA molecules in a cell  Are packaged into chromosomes 50 µm

8. Genetic Material  In animals  Somatic cells have pairs of chromosomes  46 chromosomes in humans  Gametes (egg & sperm) have one member of each pair of chromosomes  23 chromosomes in humans

9. DNA Replication  Each duplicated chromosome  Has two sister chromatids, which separate during cell division  They are attached by a central area called the centromere (1 centromere per chromosome/chromatid pair)

10. Chromosomes Chromosomal DNA molecules Centromere Chromosome arm Chromosome duplication (including DNA replication) and condensation Sister chromatids Separation of sister chromatids into two chromosomes 1 2 3

11. Phases of the Cell Cycle  The cell cycle consists of  I nterphase (about 90% of the cell cycle) divided into 3 subphases:  G 1 phase (“first gap”)  S phase (“synthesis”)  G 2 phase (“second gap”)  Mitotic (M) phase  Mitosis  Cytokinesis

12. INTERPHASE G1G1 G2G2 S MITOTIC (M) PHASE Cytokinesis Mitosis

13. Phases of the Cell Cycle  Mitosis is divided into 5 subphases  Prophase These 2 often combined into 1 phase  Prometaphase  Metaphase  Anaphase  Telophase

14. G 2 of InterphaseProphasePrometaphase Centrosomes (with centriole pairs) Chromatin (duplicated) Nucleolus Nuclear envelope Plasma membrane Early mitotic spindle Aster Centromere Chromosome, consisting of two sister chromatids Fragments of nuclear envelope Nonkinetochore microtubules Kinetochore Kinetochore microtubule Metaphase Metaphase plate AnaphaseTelophase and Cytokinesis Spindle Centrosome at one spindle pole Daughter chromosomes Cleavage furrow Nucleolus forming Nuclear envelope forming 10  m

15. G 2 of Interphase Prophase Prometaphase Centrosomes (with centriole pairs) Chromatin (duplicated) Nucleolus Nuclear envelope Plasma membrane Early mitotic spindle Aster Centromere Chromosome, consisting of two sister chromatids Fragments of nuclear envelope Nonkinetochore microtubules Kinetochore Kinetochore microtubule

16. Metaphase Metaphase plate Anaphase Telophase and Cytokinesis Spindle Centrosome at one spindle pole Daughter chromosomes Cleavage furrow Nucleolus forming Nuclear envelope forming

17. Closer Look at the Mitotic Spindle Sister chromatids Aster Centrosome Metaphase plate (imaginary) Kineto- chores Overlapping nonkinetochore microtubules Kinetochore microtubules Microtubules Chromosomes Centrosome 0.5  m 1  m

18. Cytokinesis  In animal cells  Cytokinesis occurs by a process known as cleavage, forming a cleavage furrow Cleavage furrow Contractile ring of microfilaments Daughter cells 100 µm

19. Cytokinesis  In plant cells, during cytokinesis  A cell plate forms Daughter cells 1 µm Vesicles forming cell plate Wall of patent cell Cell plate New cell wall

20. Following the Chromosome Number Summary  An imaginary somatic cell has 10 chromosomes at G 1.  How many total chromatids will it have at the end of S phase?20  How many chromosomes will it have at the end of S phase?10  How many chromosomes will it have after Anaphase?20  How many chromosomes will EACH daughter cell have AFTER cytokinesis?10

21. What Controls the Cell Cycle?  Cell cycle control system regulates cell cycle  Chemical signals in cytoplasm control system  Control system has specific checkpoints  Cell cycle stops at checkpoints until go-ahead signals are received

22. What Controls the Cell Cycle?  3 main checkpoints:  G 1 checkpoint  G 2 checkpoint  M checkpoint

23. Cell Cycle Control System Control system G 2 checkpoint M checkpoint G 1 checkpoint G1G1 S G2G2 M

24. Cell Cycle Control System: G 0 Phase G 1 checkpoint G1G1 G1G1 G0G0 Cell cycle proceeds if signal received. ( b) If signal not received, cell exits the cell cycle and goes into G 0, a nondividing state.

25. Normal Cell Behavior  In density-dependent inhibition  Crowded cells stop dividing  Most animal cells also exhibit anchorage dependence  In which they must be attached to a substratum to divide

26. Anchorage dependence Density-dependent inhibition (a) Normal mammalian cells (b) Cancer cells 20  m Cancer cells exhibit neither density-dependent inhibition nor anchorage dependence

27. Cancer (Abnormal) Cell Behavior Transformation is process of a normal cell becoming cancerous  Cancer cells may:  Not need growth factors  Make their own growth factor  Have abnormal genes in their cell control systems

28. Cancel (Abnormal) Cell Behavior  If cancer cells not detected by immune system, masses of abnormal cells grow: tumors  Benign tumor if abnormal cells remain at original site  Malignant tumor if abnormal cells invade surrounding tissues  Metastasis occurs if cancer cells export to other parts of body  Can form secondary tumors elsewhere

29. Glandular tissue Tumor Lymph vessel Blood vessel Cancer cell Metastatic tumor A tumor grows from a single cancer cell. Cancer cells invade neighboring tissue. Cancer cells spread through lymph and blood vessels to other parts of the body. Cancer cells may survive and establish a new tumor in another part of the body. 4321

30. Cancer Research More basic research needed on normal cell division More targeted therapies to prevent cancer cells from dividing but not hurting normal cells Figuring out how to use “diplomacy” with cancer cells and make them behave like normal cells again Epigenetics (control of gene expression) is a huge field of research