Cell Division: Mitosis, Meiosis, and DNA Replication

1. Chapter 6 CancerDNA Synthesis, Mitosis, and Meiosis 0

2. Passing Genes and Chromosomes to Daughter Cells following DNA replication – a cell is ready to divide cell division = cell reproduction two kinds: 1. Asexual reproduction: Only one parent Offspring are genetically identical to parent 2. Sexual reproduction Gametes are combined from two parents Offspring are genetically different from one another and from the parents

3. Eukaryotic Cell Division = Mitosis • eukaryotic cell division consists of two stages: • Mitosis- the division of the duplicated genetic material in the nucleus • Cytokinesis- the division of the cytoplasm • mitosis described by the German anatomist Walther Flemming in 1882 • thought the cell was simply growing larger between each period of cell division • now known that mitosis is a part of the life cycle of a cell • called the Cell Cycle • internal “clock” that defines the periods of DNA synthesis and replication

4. Animation: The Cell Cycle Click “Go to Animation” / Click “Play”

5. The Cell Cycle and Mitosis Cell cycle has three steps: Interphase: the DNA replicates Mitosis: the copied chromosomes are moved into daughter nuclei Mitosis occurs in somatic or body cells. Cytokinesis: the cell is split into 2 daughter cells http://www.wisc-online.com/objects/index.asp?objID=AP13604

6. Interphase Interphase has three phases: G1: cell grows, organelles duplicate time of normal cell functions and cell growth portion of cell cycle where the cell commits to division or enters into a dormancy phase (G0) S: DNA replicates G2: cell makes proteins needed to complete mitosis may not be found in all cells protein synthesis in preparation for M phase duplication of centrioles Most of the cell cycle is spent in interphase

7. BioFlix: Mitosis

8. Mitosis Mitosis produces genetically-identical daughter nuclei Mitosis is followed by cytokinesis which splits the two nuclei into two daughter cells Four stages of Mitosis: Prophase Metaphase Anaphase Telophase

9. The Duplicated Chromosome • prior to mitosis - the DNA/chromosomes must condense • they condense so much – they become visible under a regular light microscope • condensing starts in interphase and finishes in the early stages of mitosis • unique conformation • duplicated chromosomes are held together with a structure called a centromere • two duplicated chromosomes are called sister chromatids DNA condensation animation - http://www.biostudio.com/demo_freeman_dna_coiling.htm

10. The Centriole & Mitosis -mitosis requires the presence of centrioles within the cell -centriole: short cylinders of a protein known as tubulin - tubulin is organized into short “straws” – outside the nucleus -3 straws are joined together -9 straw triplets are arranged in a circle -two centrioles are put together as a pair -one centriole pair is found in cells that can divide -duplicated in the G2 phase of the cell cycle -spindle grows in between the two centriole pairs

11. Mitosis • Prophase: • 1. DNA/chromatin finish condensing to become visible • 2. the centriole pairs move apart from each other • 3. the spindleforms between the centrioles • -spindle is made up of “strands” of proteins called microtubules • (made up of tubulin) • 4. duplicated chromosomes attached to the spindle • 5. the nuclear envelope begins to disappear Spindle with chromosomes attached

12. Mitosis Metaphase: Chromosomes are aligned across the middle of the spindle area of alignment is called the metaphase plate

13. Mitosis Anaphase: centromeres split & the individual sister chromatids are pulled apart toward opposite centriole pairs ** At the end of this phase – each end of the cell has equivalent numbers of chromosomes – same number as the parent cell

14. Mitosis Telophase basically the reverse of prophase Nuclear envelopes reform around chromosomes Chromosomes revert to uncondensed form telophase is finished upon the division of the cytoplasm/the cell = cytokinesis Cytokinesis: division of the cytoplasm and the parent cell into two identical daughter cells part of telophase slightly different between animal and plant cells

15. (a) Cleavage of an animal cell (SEM) Cytokinesis • Cytokinesis – Animal Cells: • formation of a cleavage furrow in the center of the cell • cell is divided through a “purse-string” mechanism 100 m Cleavage furrow Daughter cells Contractile ring ofmicrofilaments

16. Cytokinesis Cytokinesis in Plants: Starts with vesicles forming a cell plate. contain the materials to build a new cell wall fusion of these vesicles produces a new cell wall between the two daughter plant cells.

17. Animation: Mitosis Click “Go to Animation” / Click “Play”

18. Mitosis – A Summary

19. Mitosis – A Summary

20. Cell Cycle Control and Mutation the cell cycle is a tightly controlled process before the cell moves onto the next stage in its cell cycle – must STOP and CHECK to see if everything is okay these STOP and CHECK points are called checkpoints cell must pass certain conditions to proceed onto the next stage 3 checkpoints: G1,G2, and metaphase

21. Cell Cycle Control and Mutation one factor that can change the control of the cell cycle is a mutation in a gene that functions in the cell cycle Mutation: a change in the sequence of DNA changes to DNA can change the structure and function of the protein coded by the DNA mutations may be inherited or caused by carcinogens problems in the cell cycle arise when two kinds of genes are mutated 1. Proto-oncogenes 2. Tumor suppressor genes

22. Cell Cycle Control and Mutation Proto-oncogenes: genes that code for cell cycle control proteins play normal roles in the normal cell cycle BUT when proto-oncogenes mutate - they can become oncogenes Their proteins no longer properly regulate cell division They usually overstimulate cell division

23. Cell Cycle Control and Mutation Tumor suppressor genes: genes for proteins that stop cell division if conditions are not favorable When mutated - can allow cells to override checkpoints

24. Cell Cycle Control and Mutation uncontrolled cell cycle  uncontrolled cell growth  tumor tumor formation depends on the kinds and numbers of mutations two kinds of tumors: benign and malignant (cancer) • Multiple hit model: process of cancer development requires multiple mutations • Some mutations may be inherited (familial risk) • Most are probably acquired during a person’s lifetime

25. What Is Cancer? Tumor: Unregulated cell division that form a mass of cells with no function Benign tumor: doesn’t affect surrounding tissues Malignant tumor: invades surrounding tissues; cancerous Metastasis: cells break away from a malignant tumor and start a new cancer at another location travels through the circulatory and the lymphatic systems - invades other tissues

26. Cancer Development Requires Many Mutations Progression from benign tumor to cancer requires many mutations. also requires several events to happen: 1. Angiogenesis: tumor gets its own blood supply tumor secretes growth factors  new blood vessel growth 2. Loss of contact inhibition: cells will now pile up on each other not seen in normal cells 3. Loss of anchorage dependence: enables a cancer cell to move to another location results in metastatic capacity 4. Cancer cell becomes Immortalized: cells no longer have a fixed number of cell divisions due to an enzyme called telomerase prevents the ends of a chromosome from shortening with every round of mitosis

27. What Is Cancer? Risk factors: increase a person’s risk of developing a disease Tobacco use: tobacco contains many carcinogens Alcohol consumption High-fat, low-fiber diet Lack of exercise Obesity Increasing age which weakens the immune system Cells that divide frequently such as ovarian cells

28. Cancer Detection and Treatment Early detection increases odds of survival there are different detection methods for different kinds of cancers Some cancers produce increased amount of a characteristic protein e.g. prostate cancer – PSA antigen???? Biopsy: typical method for analysis of a possible tumor surgical removal of cells or fluid for analysis Needle biopsy: removal is made using a needle Laparascope: surgical instrument with a light, camera, and small scalpel

29. Cancer Treatment Methods Chemotherapy: drugs that selectively kill dividing cells Combination of different drugs used (“cocktail”) Interrupt cell division in different ways new chemotherapies help prevent resistance to the drugs from arising PROBLEM: normal dividing cells are also killed (hair follicles, bone marrow, stomach lining) many come from nature e.g. Taxol – pacific Yew tree

30. Cancer Treatment Methods Radiation therapy: use of high-energy particles to destroy cancer cells Damages their DNA so they can’t continue to divide or grow Usually used on cancers close to the surface Typically performed after surgical removal of tumor If a person remains cancer free after treatment for 5 years they are in remission and after 10 years they are cured.