The Cell Cycle: Mitosis, Cytokinesis, and Regulation in Eukaryotic Cells

1. Chapter 9 The Cell Cycle

3. 100 µm 200 µm 20 µm (c) Tissue renewal. These dividing bone marrow cells (arrow) will give rise to new blood cells (LM). (a) Reproduction. An amoeba, a single-celled eukaryote, is dividing into two cells. Each new cell will be an individual organism (LM). (b) Growth and development. This micrograph shows a sand dollar embryo shortly after the fertilized egg divided, forming two cells (LM). The Functions of Cell Division

4. 50 µm Eukaryotic Chromosome

5. Chromosomes • Autosomes (#1-22) • Sex Chromosomes (X/Y) • Chromatin • DNA wrapped around histones • Duplicated at “S” • Sister chromatids • Attached at centromere

6. 0.5 µm A eukaryotic cell has multiplechromosomes, one of which is represented here. Before duplication, each chromosomehas a single DNA molecule. Chromosomeduplication(including DNA synthesis) Once duplicated, a chromosomeconsists of two sister chromatidsconnected at the centromere. Eachchromatid contains a copy of the DNA molecule. Centromere Sisterchromatids Separation of sister chromatids Mechanical processes separate the sister chromatids into two chromosomes and distribute them to two daughter cells. Centrometers Sister chromatids

7. Cell Cycle • Life cycle of cell • Mitosis to mitosis • Interphase • G1 • S • G2 • Mitosis • Cytokinesis

8. InterphaseG1 • First “gap” or “growth” phase • Cell Doubles in Size • Cell “does” what it is supposed to do!

9. InterphaseS • Synthesis • DNA replicates producing sister chromatids • Remain attached at the centromere

10. InterphaseG2 • Second “gap” or growth phase • Prepares for cell division by “stockpiling” proteins, building structures needed for cell division

11. Mitosis • Prophase • Chromatin coils & chromosomes appear • Nucleolus disappears • Centrosomes appear & separate to poles • Spindle fibers appear (next slide) • Prometaphase • Nuclear envelope disappears • Kinetochores appear • Spindle fibers attach at kinetochore

12. PROMETAPHASE G2 OF INTERPHASE PROPHASE Centrosomes(with centriole pairs) Aster Fragmentsof nuclearenvelope Early mitoticspindle Kinetochore Chromatin(duplicated) Centromere Nonkinetochoremicrotubules Kinetochore microtubule Chromosome, consistingof two sister chromatids Nuclearenvelope Plasmamembrane Nucleolus

13. Mitosis (cont.) • Metaphase • Chromosomes pushed to middle • Anaphase • Centromeres break • Chromatids separate  move to poles • Telophase • Reverse Prophase & Prometaphase

14. METAPHASE ANAPHASE TELOPHASE AND CYTOKINESIS Metaphaseplate Cleavagefurrow Nucleolusforming Nuclear envelopeforming Daughter chromosomes Centrosome at one spindle pole Spindle

17. Mitotic spindle • Centrosome –MTOC in both plants and animals • Centrioles (animals have them, plants don’t) • “Spin” out kinetochore and spindle fibers • Kinetochore Fibers • Begin at poles, “captured” by kinetochore • “Move” chromosomes by pushing/pulling them • Polar Spindle Fibers • Stretch from pole to pole • Elongate cell • Kinetochore • Protein & DNA • “outside” surface of chromosome at centromere

18. Cell Divides Independent of mitosis May begin during Anaphase or Telophase Plants Cell plate forms in center of cell Animals Cleavage Furrow forms on surface of cell Result=2 new daughter cells Cytokinesis

20. Regulating the Cell Cycle • Control System • Triggers/coordinates events • Checkpoints (animal cells) • G1, G2, M • Cdks • Kinases—enzymes that phosphorylate or dephosphorylate proteins • Cyclins • Molecules that activate kinases • # of molecules in cell rises/falls in a cycle • CDK’s— cyclin dependent kinases • Always present in cells • Activated by cyclins • MPF (1st discovered CDK complex) • Pushes cell past G2 into M • Switches “off” by degrading its own protein

21. 3 G1 G1 M G2 G2 S S M (a) Fluctuation of MPF activity and cyclin concentration during the cell cycle MPF activity Cyclin Relative Concentration Time (b) Molecular mechanisms that help regulate the cell cycle 1 Synthesis of cyclin begins in late S phase and continues through G2. Because cyclin is protected from degradation during this stage, it accumulates. 5 During G1, conditions in the cell favor degradation of cyclin, and the Cdk component of MPF is recycled. G1 S Cdk M G2 DegradedCyclin G2checkpoint 2 Cdk Cyclin is degraded Cyclin MPF MPF promotes mitosis by phosphorylating various proteins. MPF‘s activity peaks during metaphase. 4 During anaphase, the cyclin component of MPF is degraded, terminating the M phase. The cell enters the G1 phase.

22. Origin of replication 4 3 1 2 Cell wall Plasma Membrane E. coli cell Bacterial Chromosome Chromosome replication begins. Soon thereafter, one copy of the origin moves rapidly toward the other end of the cell. Two copies of origin Replication continues. One copy ofthe origin is now at each end of the cell. Origin Origin Replication finishes. The plasma membrane grows inward, and new cell wall is deposited. Two daughter cells result. Bacterial Cell DivisionBinary Fission

23. Cancer:Disrupting the Cell Cycle • Cancer • Happens when cells don’t respond to Cell Cycle regulation • Divide out of control • Transformation • Normal cell mutates & grows abnormally

24. Cancer:Tumors • Tumor • Mass of abnormal cells • Benign tumor • Tumor cells stay put • Malignant tumor • Tumor cells break off & invade other tissue • Metastasize