The Cell Cycle “Mitosis”

1. The Cell Cycle“Mitosis” Packet #33 Chapter #13

2. Introduction • Cell Cycle • An ordered sequence of events in the life of a dividing eukaryotic cell and is a type of asexual reproduction. • The contents of the parent’s cell nucleus is duplicated and an orderly separation of the cell’s contents is separated into two new, identical nuclei. • Two daughter cells are produced the parent cell.

3. Cell CycleThree General Stages • Interphase • G1 phase • Gap phase #1 • S phase • DNA synthesis • DNA is duplicated • DNA Replication • More to come later. • G2 phase • Gap Phase #2 • M phase • Mitotic phase • PMAT • Cytokensis

4. Interphase

5. Interphase • Interphase • Accounts for about 90%** of the cell cycle • G1 Phase • Gap Phase I • Cell grows in size • S Phase • Synthesis Phase • Copies of chromosomes and DNA are made • DNA Replication • G2 Phase • Gap Phase II • Cell grows in size

6. Mitotic Phase

7. Mitotic Phase (Mitosis)—Prophase • Prophase • Longest of mitotic phase • Chromosomes condense and become visible • Chromosomes, once duplicated, are called two sister chromatids • Two chromatids (sister chromatids) are formed by one chromosome • Mitotic spindle assembles

8. Mitotic Phase (Mitosis)—Metaphase • Chromosomes align along the middle (equatorial plane) of the cell • Microtubules attach chromosomes to opposite ends of the spindle

9. Mitotic Phase (Mitosis)—Anaphase • Anaphase • Chromosomes are pulled to the poles of the cell • Sister chromatids are separated • Centromeres divide

10. Mitotic Phase (Mitosis)—Telophase • Telophase • Nuclei (nucleus) and, nuclear envelope, reforms in daughter cells

11. Cell Cycle—Cytokinesis

12. Cell Cycle—Cytokinesis • Cytokinesis • Both daughter cells are separated and two distinctive cells are formed. • Daughter cells are pinched off from each other

13. Review

14. Review I

15. Review II

16. Review III • Interphase • DNA is duplicated • Prophase • Chromosomes condense • Anaphase • Sister chromatids separate • Telophase • Nuclei and nuclear envelope reform • Cyctokinesis • Separation of two daughter cells

17. Review IV • One cell division resulting in two daughter cells • Chromosome number, per nucleus, remains the same • Haploid results in haploid • Diploid results in diploid • No crossing over • More on this in meiosis

18. Control of the Cell Cycle

19. Control I • The steps of the cell cycle must occur in sequence and before the process can proceed to the next step, a checkpointmust be passed. • There are checkpoints for • Cell size • Determination of whether DNA replication is complete • These checkpoints are also regulated by various means • Growth factors • MPF • M phase promoting factor • Signals from other cells • Protein kinases • Cyclin-dependent protein kinases (Cdks)

20. p53 Gene • During the S phase, if the DNA is damaged, the p53 gene becomes activated and produces the p53 protein. • The p53 gene protein stimulates transcription of the gene (p21 gene) that codes for a Cdk inhibitor protein. • The p53 gene protein behaves as a transcription factor. • The Cdk inhibitor protein (p21 inhibitor protein) binds onto the S phase cyclin-Cdk complex and inactivates them. • Stopping the cell cycle.

21. Signals from Other Cells • Unicellular organisms, such as bacteria and yeasts, grow and divide as fast as they can. • Depends on the amount of nutrients available • Specialized eukaryotic cells, of a multicellular organism, must have their proliferation controlled so that individual cells only divide when necessary. • They divide to allow growth or to replace damaged/old cells.

22. Signals from Other Cells II • Retinoblastoma protein (Rb protein) is ONE example of a protein that keeps these cells from dividing however they want. • Binds onto a gene and prevents transcription. • Growth factors are used to override the “brakes.” • Once they have bound to the enzyme linked receptors, tyrosine kinase receptors, a pathway is initiated to allow the cells to replicate • Allowing the removal of the Rb protein.

23. Survival Factors • Survival factors allow cells to “survive” and if cells are deprived of them, cells will then activate intracellular suicide programs. • Programmed cell death • Apoptosis • How may programmed cell death be useful? • Fetal development • The spade-like structure of the hand/foot leads to the development of hand and feet structure due to the death cells in particular areas. • Metamorphosis • Tadpolefrog • Prevents necrosis

24. Apoptosis • Apoptosis occurs because of a series of enzymatic reactions carried out by proteases.

25. Cancer Cells

26. Cancer Cells • Cancer cells develop because of mutations that directly/indirectly impact the “proliferation control system.” • Faulty control system

27. Cancer Cells II • Proliferation genes code for proteins that promote cell division. • Anti-proliferation genes, such as the p53 gene, code for proteins that stop cell division. • Cdk • MPF • Mutation in the proliferation genes, the genes that promote cell division, causes the cell to divide “non-stop”--hence a cancer growth or tumor is formed • Mutant proliferation genes are called oncogenes • Cancer promoting genes.