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Chapter 12 The Cell Cycle

Chapter 12 The Cell Cycle. Cells. The ability of organisms to produce more of their own kind best distinguishes living things from nonliving matter Cell Theory: Living things are made of cells and cells reproduce from other cells

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Chapter 12 The Cell Cycle

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  1. Chapter 12The Cell Cycle

  2. Cells • The ability of organisms to produce more of their own kind best distinguishes living things from nonliving matter • Cell Theory: Living things are made of cells and cells reproduce from other cells • The continuity of life is based on the reproduction of cells, or cell division

  3. Genome • All the DNA in a cell constitutes the cell’s genome • A genome can consist of • Single DNA molecule • common in prokaryotic cells • Multiple DNA molecules • common in eukaryotic cells • DNA molecules in a cell are packaged into chromosomes

  4. Chromosomes • Eukaryotic chromosomes consist of chromatin, a complex of DNA and protein that condenses during cell division • Every eukaryotic species has a characteristic number of chromosomes in each cell nucleus • Somatic cells (nonreproductive cells) have two sets of chromosomes • Diploid cells (2n) • Gametes (reproductive cells: sperm and eggs) have half as many chromosomes as somatic cells • Haploid cells (n)

  5. Cellular Reproduction • Asexual Reproduction: Cells divide creating identical cells • In unicellular organisms, division of one cell reproduces the entire organism • Multicellular organisms depend on cell division for • Development from a fertilized cell • Growth • Repair

  6. Binary Fission in Bacteria • Prokaryotes (bacteria and archaea) reproduce by a type of cell division called binary fission • In binary fission, the chromosome replicates (beginning at the origin of replication), and the two daughter chromosomes actively move apart • The plasma membrane pinches inward, dividing the cell into two

  7. ChromosomalDNA molecules Mitotic Division Chromosomes Centromere • Most eukaryotes reproduce by mitosis • Since prokaryotes evolved before eukaryotes, mitosis probably evolved from binary fission • Certain protists exhibit types of cell division that seem intermediate between binary fission and mitosis Chromosomearm Chromosome duplication(including DNA replication)and condensation Sisterchromatids Separation of sisterchromatids intotwo chromosomes

  8. Cellular Reproduction • Sexual Reproduction: Gametes fuse to create zygote • Gametes formed during meiosis • a special type of division that can produce sperm and egg cells • Meiosis creates haploid cells • After fertilization, cell has unique combination of chromosomes

  9. Cell Cycle and Mitosis • Eukaryotic cells • Cycle of growth, DNA synthesis, and division • Cellular division= one cell divides into 2 cells • identical to original cell

  10. Interphase and Mitosis 1. G1 Phase= Gap 1 Phase -Cell Growth 2. S Phase= DNA Synthesis -Replication 3. G2 Phase= Gap 2 Phase -Cell Growth 4. M Phase= Mitotic Phase -Cellular Division Interphase ~90% of cell life

  11. Cell Cycle: G1 • Gap 1 Phase • Growth of cell • Increase in mass • Increase Cytoplasm • Increase Proteins • Produce Organelles • Metabolic activity is high

  12. Cell Cycle: S phase • DNA synthesis • During S phase, DNA is replicated • Occurs in nucleus • Eukaryotic cells normally have 2 copies of each chromosome- 1 set from mom, 1 set from dad • Diploid= 2 n • Haploid= n • n= number of different types of chromosomes

  13. Human Chromosomes Homologous Chromosomes= pair of chromosomes Haploid (n)=23 Diploid (2n)=46

  14. Cell Cycle: S Phase • Prepares DNA for M phase • Duplicates entire genetic code • Creates 2 new strands of DNA from existing strands • DNA synthesis uses a semiconservative model • Each DNA molecule has 1 old strand and 1 new strand

  15. Chromosomes • Diploid Cell: 2n = 6 • Haploid= n= 3 • Following DNA synthesis, each of the six chromosomes consists of 2 sister chromatids, connected at the centromere Sister Chromatids Homologous Chromosome Centromere Blue: Paternal Chromosomes Pink: Maternal Chromosomes

  16. Chromosomes • Homologous chromosomes are paired chromosomes which possess genes for the same characteristics. One chromosome comes from mom & one from dad Sister Chromatids Homologous Chromosome Centromere Blue: Paternal Chromosomes Pink: Maternal Chromosomes

  17. Cell Cycle: G2 • Gap 2 Phase • Growth of cell • Increase in mass • Makes proteins needed for mitosis • Centrosome: the microtubule organizing center • Each centrosome has pair of centrioles • The centrosome replicates during interphase

  18. Cell Cycle: M Phase • Mitotic Phase • Mitosis= Nuclear Division • Followed by Cytokinesis • Division of cytoplasm

  19. Mitosis: 5 Stages Mitosis is divided into five phases: • Prophase • Prometaphase • Metaphase • Anaphase • Telophase • Cytokinesis overlaps the latter stages of mitosis

  20. Mitosis: 5 Stages • Prophase • Chromosomes condense • The mitotic spindle is a structure made of microtubules that controls chromosome movement during mitosis • The spindle includes the centrosomes, the spindle microtubules, and the asters • Aster • a radial array of short microtubules • extends from each centrosome

  21. Mitosis: 5 Stages 2. Prometaphase • Nuclear envelope breaks up • Two centrosomes migrate to opposite ends of the cell during prophase and prometaphase • Some spindle microtubules attach to the kinetochoresof chromosomes and begin to move the chromosomes • Kinetochores are protein complexes associated with centromeres

  22. Mitosis: 5 Stages 3. Metaphase • Longest phase of mitosis • 20 minutes • Chromosomes line up at the metaphase plate • an imaginary structure at the midway point between the spindle’s two poles • For each chromosome, sister chromatids are attached at kinetochore to spindle fibers from opposite spindle poles

  23. Mitosis: 5 Stages 4. Anaphase • Shortest stage of mitosis • Cohesion proteins between sister chromatids are cleaved • Each chromatid is now an individual chromosome • Individual chromosomes are pulled to opposite ends of cells as microtubules shorten • Cell elongates as microtubules not attached at kinetochores lengthen

  24. Mitosis: 5 Stages 5. Telophase • 2 nuclei form • Nucleolus form • Nuclear envelope forms from fragments • Chromosomes become less condensed • Cytokinesis • Division of the cytoplasm • Animal cells: cleavage furrow forms and pinches cell in 2 • Plant cells: Formation of cell plate

  25. Cytokinesis

  26. Cell Cycle: M Phase • Before Mitosis: • 1 Cell= Diploid (2n) • After Mitosis: • 2 Cells= Diploid (2n) • *End product of mitosis is 2 identical cells

  27. Mitosis • Cells vary in rate of mitosis • Age matters: children vs. adult • Varies from continuously (skin cells) to only when necessary to repair damage (internal organ cells) • These differences result from regulation at the molecular level

  28. Cell Cycle • The sequential events of the cell cycle are directed by a distinct cell cycle control system • Regulated by both internal and external controls • Example of Internal Control: if kinetochore not attached to spindle microtubules, sends a molecular signal that delays anaphase • Example of External Control: growth factors • Proteins released by certain cells that stimulate other cells to divide • The clock has specific checkpoints where the cell cycle stops until a go-ahead signal is received

  29. Controls on Cell Cycle • Multiple checkpoints in cell cycle • Prevent uncontrolled growth • Repair mistakes • For many cells, the G1 checkpoint seems to be the most important • If a cell receives a go-ahead signal at the G1 checkpoint, it will usually complete the S, G2, and M phases and divide • If the cell does not receive the go-ahead signal, it will exit the cycle, switching into a nondividing state called the G0 phase

  30. Controls on Cell Cycle • Two types of regulatory proteins are involved in cell cycle control: cyclins and cyclin-dependent kinases (Cdks) • Cdks activity fluctuates during the cell cycle because it is controlled by cyclins, so named because their concentrations vary with the cell cycle • MPF (maturation-promoting factor) is a cyclin-Cdk complex that triggers a cell’s passage past the G2 checkpoint into the M phase

  31. Controls on Cell Cycle • An example of external signals is density-dependent inhibition, in which crowded cells stop dividing • Most animal cells also exhibit anchorage dependence, in which they must be attached to a substratum in order to divide

  32. Controls on Cell Cycle • Cancer is a disease of the cell cycle • Normal cell becomes cancer cell through transformation • Often results from mutations in DNA • Uncontrolled cell growth can lead to tumors • Masses of abnormal cells

  33. Controls on Cell Cycle • Benign Tumor= abnormal cells remain at the original site • Malignant tumors= invade surrounding tissues • Metastasize= export cancer cells to other parts of the body, where they may form additional tumors • Cancer cells exhibit neither density-dependent inhibition nor anchorage dependence • Cancer cells have abnormal cell cycle control system • may lack protein checkpoints, produce own growth factors or convey growth signal without growth factor

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