1.  Chapter 12~ The Cell Cycle

2. Big mitosis question: how do eukaryotic cells divide to produce genetically identical cells? One cell Two identical daughter cells

3. How is cell division different for prokaryotes (bacteria and archaea) than eukaryotes?  Cell division in bacteria is called: Binary fission Only one circular chromosome to replicate (copy!).  What organelles do the same? Mitochondria and chloroplasts! What can we infer about the evolution of these organelles?

4. Why do cells need to undergo mitosis?  Growth How do multicellular organisms grow? Make more cells! (some cells just get bigger – like adipose (fat) cells and muscle cells.)  Repair  Replacement (old cells may undergo apoptosis and need to be replaced) Asexual reproductionAsexual reproduction

5. The Problem (in eukaryotes)? If chromosomes (DNA molecules) were like pasta, which would be easier to pull apart into individual pieces A plate of tangled spaghetti Or a plate of macaroni? Eukaryotic DNA

6. Cell Division: Key Roles  Genome: cell’s genetic information cell’s genetic information  Somatic cells body cells body cells  Gametes reproductive cells: sperm and egg cells reproductive cells: sperm and egg cells  Chromosomes: DNA molecules  Diploid (2n): 2 sets of chromosomes 2 sets of chromosomes  Haploid (1n): 1 set of chromosomes 1 set of chromosomes  Chromatin: DNA-protein complex DNA-protein complex  Sister Chromatids: replicated strands of a chromosome replicated strands of a chromosome  Centromere: narrowing “waist” of sister chromatids narrowing “waist” of sister chromatids  Mitosis: nuclear division nuclear division  Cytokinesis: cytoplasm division cytoplasm division  Meiosis: gamete cell division gamete cell division

7. The Cell Cycle  Interphase (90% of cycle) G1 phase~ growth of cell (after cytokinesis) G1 phase~ growth of cell (after cytokinesis) S phase~ synthesis of DNA S phase~ synthesis of DNA G2 phase~ make preparation for cell division G2 phase~ make preparation for cell division  Mitotic phase Mitosis~ nuclear division Mitosis~ nuclear division Cytokinesis~ cytoplasm division Cytokinesis~ cytoplasm division Watch This! Watch This! Watch This Watch This

8. Mitosis  Prophase  Prometaphase  Metaphase  Anaphase  Telophase  Watch this… Watch this… Watch this…

9. Prophase  Chromosomes visible  Nucleoli disappear  Sister chromatids  Mitotic spindle forms  Centrosomes move

10. Prometaphase  Nuclear membrane fragments  Spindle interaction with chromosomes  Kinetochore develops

11. Figure 12.7a 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

12. Metaphase  Centrosomes at opposite poles  Centromeres are aligned  Chromosomes lined up on central plain  Kinetochores of sister chromatids attached to microtubules (spindle)

13. Anaphase  Paired centromeres separate; sister chromatids liberated  Chromosomes move to opposite poles  Each pole now has a complete set of chromosomes

14. Telophase  Daughter nuclei form  Nuclear envelopes arise  Chromatin becomes less coiled  Two new nuclei complete mitosis

15. Figure 12.7b Metaphase Metaphase plate Anaphase Telophase and Cytokinesis Spindle Centrosome at one spindle pole Daughter chromosomes Cleavage furrow Nucleolus forming Nuclear envelope forming

16. Cytokinesis  Cytoplasmic division  Animals: cleavage furrow  Plants: cell plate

18. Cell Cycle Regulation  Growth factors  Anchorage dependence  Density-dependent inhibition As a Cyclin (a protein) builds up because checks are going well, it binds to…. binds to…. Cyclin dependent kinase (there are several)- enzymes that change shape and phosphorylate other proteins in a transduction signal that leads to passing the checkpoint.

19. Cell Cycle Checkpoints  At checkpoints, specialized proteins determine whether the necessary conditions exist. Yes – enters next phase No – cycle stops Errors – cell death, cancer, too many or too few chromosomes in new cell, mistakes in copying of DNA (mutations)

20. G 1 Checkpoint  Are conditions OK? Cell size OK? Cell size OK? Environmental conditions good? Environmental conditions good? Appropriate signals from other cells (growth factors)? Appropriate signals from other cells (growth factors)? No? -Enters G 0. Some cells normally in G 0 – nerve cells, skeletal muscle cells No? -Enters G 0. Some cells normally in G 0 – nerve cells, skeletal muscle cells

21. G 2 Checkpoint  During G2 phase, cyclins and CDK proteins check for DNA replication completion DNA replication completion DNA damage/mutations DNA damage/mutations Make repairs if needed before entering mitosis Make repairs if needed before entering mitosis Cell size, organelles Cell size, organelles  If everything OK – enters M phase

22. M Checkpoint  Happens mid- mitosis  Are chromosomes properly attached to spindle fibers? Ensures daughter cells will not have unbalanced number of chromosomes - aneuploidy Ensures daughter cells will not have unbalanced number of chromosomes - aneuploidy

23. Nondisjunction due to problem with spindle fiber connections  Trisomy 21 or Down’s Syndrome

24. Figure 12.17 (b) Molecular mechanisms that help regulate the cell cycle MPF activity Cyclin concentration M M M S S G1G1 G2G2 G1G1 G2G2 G1G1 Cdk Degraded cyclin Cyclin is degraded MPF G 2 checkpoint Cdk Cyclin M S G1G1 G2G2 Time (a) Fluctuation of MPF activity and cyclin concentration during the cell cycle Cyclin Dependent Kinases are control molecules for cell cycle

25. Why programmed suicide?  Proper development.  The readsorption of the tadpole tail  The formation of the fingers and toes of the fetus  The sloughing off of the inner lining of the uterus (the endometrium) at the start of menstruation

26. Why apoptosis (cell suicide)?  Destroys cells that are a threat :  Cells infected with viruses  Cells of the immune system prevent them from attacking body when done prevent them from attacking body when done Defects autoimmune diseases: lupus, rheumatoid arthritis Defects autoimmune diseases: lupus, rheumatoid arthritis  Specific to cell cycle: Cells with DNA damage Cells with DNA damage Birth defectsBirth defects CancerousCancerous Respond to DNA damage by increasing production of p53 proteinRespond to DNA damage by increasing production of p53 protein Cancer cells Cancer cells Radiation and chemicals used in cancer therapy induce apoptosis in some types of cancer cellsRadiation and chemicals used in cancer therapy induce apoptosis in some types of cancer cells

27. Cancer  Transformation: defect in regulation of cell cycle  Mutation in somatic cells/mutation in germ line  Proto-oncogenes: stimulate regular cell division – a “Go” signal for mitosis  Oncogenes: mutated forms of proto-oncogenes– promote uncontrolled division - cause cancer  Tumor suppressor genes: prevent cell division- these are often genes that code for CDKs - control genes  DNA repair genes fix mutations in cell cycle genes

29. Make a hypothesis:  Question: How might the chromosomes of a cancer cell appear in comparison to a normal cell? How might the chromosomes of a cancer cell appear in comparison to a normal cell? How are those differences related to the behavior of the cancer cell? How are those differences related to the behavior of the cancer cell?

30. Cancer cells  Liver cancer What do you already know about cancer? Think about ways the cancer cell might be different from normal cells,healthy cells. Cell division in cancer cells IS fundamentally different than in normal cells.

31. Cancer  Tumor: benign or malignant  Metastasis  CIN – cervical intra epitheleal dysplasia epitheleal dysplasia

32. Make a hypothesis:  How might the chromosomes of a normal, healthy cell appear in comparison to a cancer cell? Healthy cell chromosomes (karyotype) Male or female??

33. HeLa vs. Normal cell karyotype

34. P53 is a protein coded by a tumor suppressor gene The “guardian of the genome”  p53 tumor suppressor gene products interact with cdk2 – a “stop signal” for mitosis (G2 checkpoint).  P53 known as guardian of the genome- protects cells exposed to radiation, UV, chemicals  Mutant p53 can’t act as stop signal In 50-60% of tumor types In 50-60% of tumor types

35. P53 (a gene regulator)   It can activate DNA repair proteins when DNA has sustained damage. Thus, it may be an important factor in aging. [27]DNA repairaging [27]   It can arrest growth by holding the cell cycle at the G1/S regulation point on DNA damage recognition (if it holds the cell here for long enough, the DNA repair proteins will have time to fix the damage and the cell will be allowed to continue the cell cycle).cell cycleG1/S regulation point   It can initiate apoptosis - programmed cell death - if DNA damage proves to be irreparable.apoptosis

36. How p53 works   p53 binds DNA and activates expression of several genes including p21 and hundreds of other down- stream genes.p21   p21 binds to the G1-S/CDK (CDK4/CDK6, CDK2, and CDK1) complexes (molecules important for the G1/S transition in the cell cycle) inhibiting their activity.G1SCDKCDK4CDK6CDK2CDK1G1/S transition   CDKs at work here!!! (back to slide 24)   P53 is typically bound to pink molecule and inhibits expression of genes that control cycle.   When it is activated, binds to DNA and promotes expression of genes that do the following:

37. HPV and cervical cancer  Protein expressed by HPV virus degrades p53  Interferes with other apoptosis mechanisms  Interferes with Rb gene – another major tumor suppressor gene (G1 checkpoint) – resulting in uncontrolled division  P53 and Rb interference causes accumulated chance errors unchecked by repair or cell death.

38. Philadelphia chromosome Philadelphia chromosome